The Open Parasitology Journal




ISSN: 1874-4214 ― Volume 6, 2018
RESEARCH ARTICLE

Factors Affecting Helminth Abundances in Synanthropic Rodents of an Urban Environment



Diego Hancke1, 2, *, Olga Virginia Suárez1, 2
1 Laboratorio de Ecología de Roedores, Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria, PB II, 4to piso, C1428EHA Ciudad Autónoma de Buenos Aires, Argentina
2 Instituto de Ecología, Genética y Evolución de Buenos Aires (IEGEBA), UBA-CONICET, Intendente Gu¨iraldes 2160, Ciudad Universitaria, PB II, 4to piso, C1428EHA Ciudad Autónoma de Buenos Aires, Argentina

Abstract

Background:

Current levels of urbanization cause changes in the ecology of hosts, the pathogens, or both, promoting the proliferation of zoonotic diseases. Rodents are a good biological model for the development of pathogen transmission models because it presence is often related to a none-adequate environmental management.

Objective:

The main goal of this paper was to study the changes in the abundance of helminth populations in synanthropic rodents of an urban landscape.

Methods:

A total of 92 R. norvegicus and 65 M. musculus were captured in the City of Buenos Aires (Argentina) and were screened for parasites. The variations in helminth abundances were studied at host population scale to determine the factors, such as the type of environment, meteorological conditions and demographic parameters of the hosts, which have an effect on helminth infection rates.

Results:

Parasites with intermediate hosts or free living larval stages in their life cycle were the most affected. It was found how rodents’ use of the habitats in the different urban environments has an effect on the helminth infection levels. Besides, the importance of season on helminth abundance was determined, suggesting that climatic conditions are crucial for parasite survival and transmission.

Conclusion:

This information is relevant because it not only allows us to deepen the ecological dynamics of parasites in urban rodents, but also shows that environmental conditions are determinants for the persistence of helminth populations in a city.

Keywords: Helminths, Rodents, Urbanization, Ecology, Zoonosis, Buenos Aires.


Article Information


Identifiers and Pagination:

Year: 2018
Volume: 6
First Page: 87
Last Page: 95
Publisher Id: TOPARAJ-6-87
DOI: 10.2174/1874421401806010087

Article History:

Received Date: 22/6/2018
Revision Received Date: 1/10/2018
Acceptance Date: 8/10/2018
Electronic publication date: 29/10/2018
Collection year: 2018

Article Metrics:

CrossRef Citations:
0

Total Statistics:

Full-Text HTML Views: 178
Abstract HTML Views: 104
PDF Downloads: 69
ePub Downloads: 65
Total Views/Downloads: 416

Unique Statistics:

Full-Text HTML Views: 129
Abstract HTML Views: 66
PDF Downloads: 55
ePub Downloads: 42
Total Views/Downloads: 292
Geographical View

© 2018 Diego and Virginia.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to the author at the Laboratorio de Ecología de Roedores, Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Avenida Intendente Cantilo s/n, Ciudad Universitaria, Pabellón II, 4º Piso Laboratorio 104 (C1428EHA), Buenos Aires, Argentina, Tel: +541145763300int219; Fax: +541145763354; E-mail: diegohancke@ege.fcen.uba.ar




1. INTRODUCTION

The current levels of human–ecosystem interaction result in a habitat transformation and changes in the ecology of the host, the pathogen, or both, promoting thus an alteration in disease transmission dynamics [1Thompson RC. Parasite zoonoses and wildlife: One Health, spillover and human activity. Int J Parasitol 2013; 43(12-13): 1079-88.[http://dx.doi.org/10.1016/j.ijpara.2013.06.007] [PMID: 23892130] , 2Hassell JM, Begon M, Ward MJ, Fèvre EM. Urbanization and disease emergence: Dynamics at the wildlife-livestock-human interface. Trends Ecol Evol (Amst) 2017; 32(1): 55-67.[http://dx.doi.org/10.1016/j.tree.2016.09.012] [PMID: 28029378] ]. Urbanization is a phenomenon that accelerates and intensifies these impacts on zoonotic diseases [3Mackenstedt U, Jenkins D, Romig T. The role of wildlife in the transmission of parasitic zoonoses in peri-urban and urban areas. Int J Parasitol Parasites Wildl 2015; 4(1): 71-9.[http://dx.doi.org/10.1016/j.ijppaw.2015.01.006] [PMID: 25830108] , 4Neiderud CJ. How urbanization affects the epidemiology of emerging infectious diseases. Infect Ecol Epidemiol 2015; 5: 27060.[http://dx.doi.org/10.3402/iee.v5.27060] [PMID: 26112265] ]. This is particularly observed for urban rodents because of the synanthropic behavior of these animals [5Morand S, Bordes F, Chen HW, et al. Global parasite and Rattus rodent invasions: The consequences for rodent-borne diseases. Integr Zool 2015; 10(5): 409-23.[http://dx.doi.org/10.1111/1749-4877.12143] [PMID: 26037785] ].

Mus musculus and Rattus norvegicus are among the best urban adapted rodents. Originated from Southeast Asia, various aspects of their biology, such as enormous reproductive potential, feeding benefited by accumulated or discarded human food, adaptations to urban environments, contribute to their success worldwide [6Kosoy M, Khlyap L, Cosson JF, Morand S. Aboriginal and invasive rats of genus rattus as hosts of infectious agents. Vector Borne Zoonotic Dis 2015; 15(1): 3-12.[http://dx.doi.org/10.1089/vbz.2014.1629] [PMID: 25629775] ]. Synanthropic rodents are the main reservoirs or host for different human pathogens, including zoonotic helminth species [7Himsworth CG, Parsons KL, Jardine C, Patrick DM. Rats, cities, people, and pathogens: A systematic review and narrative synthesis of literature regarding the ecology of rat-associated zoonoses in urban centers. Vector Borne Zoonotic Dis 2013; 13(6): 349-59.[http://dx.doi.org/10.1089/vbz.2012.1195] [PMID: 23590323] ]. The presence of murine rodents in anthropogenic habitats could be the reason for many of the parasitological studies performed worldwide [5Morand S, Bordes F, Chen HW, et al. Global parasite and Rattus rodent invasions: The consequences for rodent-borne diseases. Integr Zool 2015; 10(5): 409-23.[http://dx.doi.org/10.1111/1749-4877.12143] [PMID: 26037785] ], increasing the detection of rodent transmitted pathogens in last decades [8Bordes F, Blasdell K, Morand S. Transmission ecology of rodent-borne diseases: New frontiers. Integr Zool 2015; 10(5): 424-35.[http://dx.doi.org/10.1111/1749-4877.12149] [PMID: 26176684] ].

In the City of Buenos Aires (Argentina) (CBA), the community of rodents and their parasites has been studied for more than a decade. The establishment and proliferation of these animals are affected by the urban context, varying rodent composition according to habitat characteristics. Rattus norvegicus and M. musculus are the most common species and are the dominant species in two different landscape units of the CBA: shantytowns and parks or green spaces [9Cavia R, Cueto GR, Suárez OV. Changes in rodent communities according to the landscape structure in an urban ecosystem. Landsc Urban Plan 2009; 90: 11-9.[http://dx.doi.org/10.1016/j.landurbplan.2008.10.017] ].

The helminth fauna of R. norvegicus and M. musculus of the CBA was recently described, exhibiting each rodent species its own characteristics in terms of richness, diversity and composition [10Hancke D, Suárez OV. Helminth diversity in synanthropic rodents from an urban ecosystem. EcoHealth 2017; 14(3): 603-13.[http://dx.doi.org/10.1007/s10393-017-1239-8] [PMID: 28417211] ]. A high similarity was seen in the structure of the infracommunities of R. norvegicus from shantytowns and parklands, probably related to similar environmental characteristics that predict the presence of brown rats in both landscape units [11Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669] ]. In contrasts, M. musculus is preferably captured inside the houses in shantytowns, exploiting thus microhabitats with different conditions regarding the specimens captured in parks, which result in quantitative differences between infracommunities from both landscape units [11Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669] ]. However, the factors affecting the abundance of helminth populations of urban rodents are still unknown.

Parasites have been considered as excellent bioindicators of processes occurring in an ecosystem because their life cycles depend on the presence of intermediate hosts or are involved in trophic chains or its survival and development occur in specific environmental physical-chemical ranges, among many others [8Bordes F, Blasdell K, Morand S. Transmission ecology of rodent-borne diseases: New frontiers. Integr Zool 2015; 10(5): 424-35.[http://dx.doi.org/10.1111/1749-4877.12149] [PMID: 26176684] , 12Froeschke G, Matthee S. Landscape characteristics influence helminth infestations in a peri-domestic rodent--implications for possible zoonotic disease. Parasit Vectors 2014; 7: 393.[http://dx.doi.org/10.1186/1756-3305-7-393] [PMID: 25159989] ]. The greatest abundances of each parasite species are thus expected in sites where the resources (including the hosts) are in full and the conditions are propitious for the transmission and survival of free life stages [13Lagrue C, Poulin R. Spatial covariation of local abundance among different parasite species: The effect of shared hosts. Parasitol Res 2015; 114(10): 3637-43.[http://dx.doi.org/10.1007/s00436-015-4590-0] [PMID: 26113509] ]. The main goal of this paper is to study the changes of the abundance in helminth populations of R. norvegicus and M. musculus captured in the CBA and analyze the factors that explain these variations. It is expected that helminths with indirect life cycles were more affected by external factors than those with direct cycles and covariations are expected to occur between parasite species with similar life cycles and resource requirements.

2. MATERIALS AND METHODOLOGY

The study was carried out in Buenos Aires (34º37 'S; 58º24 'W), the main city of Argentina in terms of population and one of the largest metropolises in the world [14United Nations. World Urbanization Prospects: The 2014 Revision 2014.]. Information about the study area, rodent collection and parasitological prospection is provided in detail in Hancke and Suárez (2017) [10Hancke D, Suárez OV. Helminth diversity in synanthropic rodents from an urban ecosystem. EcoHealth 2017; 14(3): 603-13.[http://dx.doi.org/10.1007/s10393-017-1239-8] [PMID: 28417211] ]. For the purpose of this paper, a total of 157 rodents, 92 R. norvegicus and 65 M. musculus, captured in 4 shantytowns and 3 parklands were analyzed.

First, possible variations in the abundance between landscape units were analyzed for both rodent species. Abundance was estimated by trap success and calculated as the proportion of traps with captured animals out of the total number of trap-nights for each site in each trapping survey. The relationship between trap success of R. norvegicus and trap success of M. musculus was analyzed for shantytowns, parks and totally by linear regressions. For each rodent species, trap successes between shantytowns and parklands were compared by analyses of variances (ANOVA). Trap success was root square transformed to meet normality assumption.

In parasitological studies, it is recommended to define the limits of parasite populations or communities at different scales. According to Bush et al. (1997) [15Bush AO, Lafferty KD, Lotz JM, Shostak AW. Parasitology meets ecology on its own terms: Margolis et al. revisited. J Parasitol 1997; 83(4): 575-83.[http://dx.doi.org/10.2307/3284227] [PMID: 9267395] ]:

Infracommunities refer to a community of infrapopulations, which include all individuals of a parasite species in a single host at a particular time. Component community refers to all infrapopulations of parasites associated with a subset of hosts in a particular time and place (or in a given ecosystem). Prevalence, mean intensity (I) and abundance (A) were calculated to describe the distribution of each parasite species in both host species following as recommended by Bush et al. (1997) [15Bush AO, Lafferty KD, Lotz JM, Shostak AW. Parasitology meets ecology on its own terms: Margolis et al. revisited. J Parasitol 1997; 83(4): 575-83.[http://dx.doi.org/10.2307/3284227] [PMID: 9267395] ].

For each host species, Permutational Multivariate Analyses of Variance (PERMANOVA) [16Anderson MJ. A new method for non-parametric multivariate analysis of variance. Austral Ecol 2001; 26: 32-46.] were performed to study the effects of trapping season and landscape unit on the composition of infracommunities. To test if helminth species are independent of each others, the adjustment of the distribution of infracommunity richness frequencies to the model of Janovy et al., (1995) [17Janovy J Jr, Clopton RE, Clopton DA, Snyder SD, Efting A, Krebs L. Species density distributions as null models for ecologically significant interactions of parasite species in an assemblage. Ecol Modell 1995; 77: 189-96.[http://dx.doi.org/10.1016/0304-3800(93)E0087-J] ] was studied for both rodent species. This model assumes that, in the absence of associations and interactions among parasite species, the distribution of the observed frequencies of the infra-community richness can be predicted by the prevalence values of each of the parasite species. Therefore, each species would have an associated probability of infection which would be independent of the presence of other species in that host. All distributions were tested using the Chi-Square goodness of fit test.

Zero-Inflated Negative Binomial models (ZINB) were performed to study the relationship between the abundance of the helminth infrapopulations and the characteristics of the hosts [18Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM. Mixed effects models and extensions in ecology with R 2009.[http://dx.doi.org/10.1007/978-0-387-87458-6] ]. Only the species whose prevalence values were equal or greater than 10% were included. ZI distributions can be viewed as a two-part model, in which the probability of species presence and abundance are modeled from the same data [19Wenger SJ, Freeman MC. Estimating species occurrence, abundance, and detection probability using zero-inflated distributions. Ecology 2008; 89(10): 2953-9.[http://dx.doi.org/10.1890/07-1127.1] [PMID: 18959332] ]. Particularly in Zero-Inflated Negative Binomial (ZINB) models, the probability of a zero outcome is modeled by logistic regression, while the continuous count is modeled by using a negative binomial error structure. The separate occurrence and abundance terms can represent different mechanisms due to factors operating at different temporal or spatial scales [19Wenger SJ, Freeman MC. Estimating species occurrence, abundance, and detection probability using zero-inflated distributions. Ecology 2008; 89(10): 2953-9.[http://dx.doi.org/10.1890/07-1127.1] [PMID: 18959332] ]. The number of worms per rat was considered as the dependent variable, whereas factors such as landscape units, season, sex, year, body length (covariable), abundance of R. norvergicus (covariable) and abundance of M. musculus (covariable) were tested in both the logistic and the negative binomial parts of the model as potential independent variables. The ZINB models were fitted manually, testing the significance of factors, covariable and interactions, first of the binomial part and then of the count part. The models were then progressively simplified by backward deletion and only significant terms (P < 0.05) were left in the final models. The models were selected with likelihood ratio tests and Akaike information criteria (AIC). For the particular cases of helminth species with low-intensity values, in this case, it makes more sense to evaluate the presence and not abundance, generalized linear models assuming a distribution of binary binomial errors or Bernoulli (presence / absence) with logit link function were conducted.

The relationship between the abundances of the most representative helminth species in each host species was tested in pairs with ZINB models. In each case, the abundance of one of the helminth species was considered as a dependent variable and the other as explanatory variable. As in the previous ZINB models, each host was considered asthe experimental unit. Given the small abundances of Hymenolepis nana and Hydatigera taeniaeformis, the presence instead of abundance was used as an explanatory variable. As the abundance of parasite can vary between environments, the landscape unit was included as a fixed factor.

All calculations were performed using the R version 2.15.1 [20R Development Core Team. R: A language and environment for statistical computing 2014. Available from: http://www.R-project.org/]. PERMANOVA analysis was performed using the vegan package [21Oksanen AJ, Blanchet FG, Kindt R. Package ‘vegan’ version 2.5-2. 2018]. ZINB models were fitted with pscl package [22Maimone C, Fearon J, Jackman MS. Package ‘pscl.’ 2012.] and all likelihood ratio tests were carried out in lmtest package [23Hothorn T, Zeileis A, Farebrother RW, Cummins C, Millo G, Mitchell D. Package “lmtest” 2018.].

3. RESULTS

The abundances (or trap success) for R. norvegicus and M. musculus were independent of each other considering the total of the sites (slope=0.35, 95% CI [-0.72, 1.42], p>0.05, R2 = 0.02) as well as considering shantytowns only (slope=-0.94, 95% CI [-3.09, 1.21], p > 0.05, R2 = 0.08). For parklands, a positive relationship was observed between the trapping success of both rodent species (slope=1.43, 95% CI [0.44, 2.48], p<0.05, R2 = 0.50). While comparing abundance of the rodent, a higher trap success was detected in M. musculus in shantytowns (ANOVA, N = 25, F = 8.37, p <0.05) while no differences were observed for R. norvegicus (ANOVA, N = 25, F = 0.39, p > 0.05).

Rattus norvegicus was parasitized with a total of 8 helminth species (8 in parklands and 5 in shantytowns) while M. musculus harboured the same 4 species in both landscape units. Fig. (1) shows variations in the prevalence of these species between landscape units for both hosts. A more detailed information about the infection parameters is provided in Hancke and Suárez (2017) [11Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669] ]. The PERMANOVA analysis revealed that the variations in the composition of infracommunities varied differently in R. norvegicus and in M. musculus Table 1. An interaction was observed between landscape units and the time of capture in brown rats. The effect of the time of capture was thus analyzed for each landscape unit separately and a significant effect was detected only for rats captured in parklands (shantytowns: PERMANOVA, Pseudo-F = 2.098, p> 0.05; parks: PERMANOVA, Pseudo-F = 2.971, p <0.05). For M. musculus, variations in the composition of infracommunities were detected between landscape units and between capture seasons Table 1.

Fig. (1)
Prevalence (%) (with std errors) for the helminth species of R. norvegicus and M. musculus from shantytowns and parklands of the City of Buenos Aires. Acantocephalans: Mm – Moniliformis moniliformis (Bremser, 1811); Cestodes; Ht – Hydatigera taeniaeformis (Batsch, 1786); Hd – Hymenolepis diminuta (Rudolphi, 1819); Hn – Hymenolepis nana (Siebold, 1852); Nematodes; Gn – Gongylonema neoplasticum (Fibiger et Ditlevsen, 1914); Nb – Nippostrongylus brasiliensis (Travassos, 1914); Csp – Capillaria sp.; Hs – Heterakis spumosa Schneider, 1866.


Table 1
Output of PERMANOVA analysis examining the helminth composition variations between landscape units and trapping seasons in R. norvegicus and M. musculus captured in the City of Buenos Aires.


The distributions of the frequencies of species richness for both hosts did not differ from those expected by the Janovy model (R. norvegicus: χ 2 = 0,009; gl= 5; p= 0,999 (shantytowns), χ 2 = 0,334; gl= 8; p = 0,999 (parks); M. musculus: χ 2 = 0,007; gl= 4; p= 0,999 (shantytowns), χ 2 = 0,025; gl= 4; p = 0,999 (parks)). This means that the probability of infection by a single helminth species remains independent of the other species of an infracommunity. Table 2 summarizes the results of the generalized linear models for the factors affecting the helminth abundance. In the case of R. norvegicus, the type of landscape unit affected 3 species. On one hand, shantytowns had a positive effect on the presence of Hymenolepis diminuta and on the abundance of Nippostrongylus brasiliensis, while on the other side, parks had it on the presence of H. nana. Besides, the colder trapping season affected negatively the presence of H. diminuta and H. nana and negatively the abundance of H. spumosa. Both cestodes, H. diminuta and H. nana, were also affected by host gender and body length of R. norvegicus, while the abundance of N. brasiliensis and H. spumosa in rats were negatively and positively associated with the trap success of M. musculus respectively. In the case of M. musculus, the abundance of N. brasiliensis was positively affected by the colder trapping season and the trapping success of R. norvegicus and negatively with the abundance of M. musculus. Hydatigera taeniaeformis was analyzed for both rodent species, but no significant associations were found.

Table 2
Summary of the results of the generalized linear models performed to analyze the factors that have an effect on the presence and abundance of helminths in R. norvegicus and M. musculus of the City of Buenos Aires (significant codes: “·” 0.05<p<0.1; “*” 0.01<p<0.05; “**” 0<p<0.01) (effect: “+” positive; “-” negative).


Regarding the interspecific helminth covariations, only significant effects were found on the abundance of H. diminuta. On one hand, the probability of infection of this cestode was positively associated with the abundance of H. spumosa (p <0.05), while on the other hand, its abundance increased with the presence of H. nana (p <0.05) (Fig. 2).

Fig. (2)
Graphs representing the mean abundance of H. spumosa of infracommunities of R. norvegicus with and without H. diminuta(A) and the mean abundance of H. diminuta of infracommunities with and without H. nana(B). Bars represents the standard errors.


4. DISCUSSION

According to previous studies, helminth infracommunities of urban rodents could be grouped according to composition and relative abundances and they respond to the structure of the host community [11Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669] ]. In this paper, we analyzed the variations in helminth abundances at a host population scale and identified the factors affecting the principal parasite species. Rodents are the main reservoirs or hosts of parasites relevant for public health. In this study, the presence of H. nana and H. diminuta confirms this role. Rodents represent a good biological model for the development of pathogen transmission models in urban landscapes because its presence is often a consequence of none-adequate environmental managements.

The type of urban landscape unit had a significant effect on the two intestinal cestodes found in our study. On one hand, a higher prevalence of H. diminuta was observed in shantytowns, showing that the conditions here favor the proliferation of arthropod pests as Tenebrio castaneum and T. confusum, both intermediate hosts of H. diminuta [24Hancke D, Suárez OV. Infection levels of the cestode Hymenolepis diminuta in rat populations from buenos aires, argentina. J Helminthol 2016; 90(2): 199-205.[http://dx.doi.org/10.1017/S0022149X15000164] [PMID: 25869333] ]. On the other hand, parks favor the presence of H. nana. This parasite is the most common cestode found in humans around the world, especially in children from poor areas [25Roberts LS, Janovy J. Foundations of Parasitology 8th ed. 8th ed.2009., 26Malheiros AF, Mathews PD, Lemos LMS, Braga GB, Shaw JJ. Prevalence of Hymenolepis nana in indigenous Tapirapé ethnic group from the brazilian amazon. Am J Biomed Res 2014; 2: 16-8.[http://dx.doi.org/10.12691/ajbr-2-2-1] ]. The parks sampled in our study area were located on the banks of rivers on whose shorelines precarious settlements not far from the parks take place. This situation would favor a greater organic matter contamination which could act as a source of intestinal parasite cysts or eggs, among other pathogens. However, despite both species were favored by different urban habitats at a landscape scale, a positive association between both species was observed. Hymenolepis nana is the only known cestode species that presents a direct cycle and occasionally uses arthropods as intermediate hosts, the same as H. diminuta. It could be hypothesized that both species may be responding at a microscale to similar biotic and abiotic factors, mediating also intermediate hosts the transmission of H. nana in R. norvegicus.

This is in concordance with the fact that both cestodes were also affected by the time of capture, decreasing both prevalences in the colder months. The development of intermediate host’s life cycle depends on optimal temperature and humidity conditions, affecting thus the abundance of the parasite [27Robinson WH. Urban insects and arachnids: A handbook of urban entomology 2015.]. Warmer months favor also the abundance of H. spumosa in R. norvegicus. Season is mentioned to affect the behavior of rats within urban environments, which could produce seasonal variations in the infection parameters of parasite populations [28Himsworth CG, Jardine CM, Parsons KL, Feng AYT, Patrick DM. The characteristics of wild rat (Rattus spp.) populations from an inner-city neighborhood with a focus on factors critical to the understanding of rat-associated zoonoses. PLoS One 2014; 9(3): e91654.[http://dx.doi.org/10.1371/journal.pone.0091654] [PMID: 24646877] ]. The fact that H. diminuta and H. spumosa were both favored by warmer conditions could explain the positive relationship observed between both species. Besides, the time of capture also affected N. brasiliensis in M. musculus, but in this case, colder months favored the presence of this nematode. Seasonal variations in N. brasiliensis have been previously reported but for R. norvegicus captured in a shantytown of CBA [29Hancke D, Navone GT, Suárez OV. Endoparasite community of Rattus norvegicus captured in an urban area of Argentina. Helminthologia 2011; 48: 167-73.[http://dx.doi.org/10.2478/s11687-011-0025-3] ]. As N. brasiliensis is a soil transmitted helminth and whose larval stages require adequate soil moisture conditions and are not resistant to desiccation, its surveillance in the environment is possibly conditioned in the warmer months of the year [30Anderson RC. Nematode parasites of vertebrates: Their development and transmission 2000.[http://dx.doi.org/10.1079/9780851994215.0000] ].

Host density and body length were also mentioned to be important factors that influence helminth infection rates, especially for directed transmitted parasite [31Arneberg P. Host population density and body mass as determinants of species richness in parasite communities: Comparative analyses of directly transmitted nematodes of mammals. Ecography 2002; 25: 88-94.[http://dx.doi.org/10.1034/j.1600-0587.2002.250110.x] ]. In our study, the infection likelihood of N. brailiensis in mice was favoured by greater densities of R. norvegicus. The abundance of this nematode was high in R. norvegicus (over 80%), so the infection of N. brailiensis in M. musculus is possibly related to the presence of brown rats, particularly in parks where the abundance of both rodents co-varied . Besides, the negative effect of mice abundance on the presence of N. brasiliensis is probably masking an effect of landscape unit more than an effect of population density itself, because a significant lower trap success for M. musculus was detected in parks.

Spatial variations in infection rates have already been described for a wide range of intestinal helminth communities for rodents in urban environments [12Froeschke G, Matthee S. Landscape characteristics influence helminth infestations in a peri-domestic rodent--implications for possible zoonotic disease. Parasit Vectors 2014; 7: 393.[http://dx.doi.org/10.1186/1756-3305-7-393] [PMID: 25159989] , 24Hancke D, Suárez OV. Infection levels of the cestode Hymenolepis diminuta in rat populations from buenos aires, argentina. J Helminthol 2016; 90(2): 199-205.[http://dx.doi.org/10.1017/S0022149X15000164] [PMID: 25869333] , 32Zain SNM, Behnke JM, Lewis JW. Helminth communities from two urban rat populations in Kuala Lumpur, Malaysia. Parasit Vectors 2012; 5: 1-23.[PMID: 22212459] ]. In our study area, while analyzing the variations of infracommunities in terms of composition, M. musculus exhibited differences between shantytowns and parklands. Mus musculus in both landscape units make use of different types of microhabitats because in shantytowns, it was trapped mainly inside the housings (in contrast to R. norvegicus who was captured mainly outside). For R. norvegicus, no differences were detected between the composition of infracommunities from shantytowns and parks, because the landscape unit did not affect the presence of the core species [10Hancke D, Suárez OV. Helminth diversity in synanthropic rodents from an urban ecosystem. EcoHealth 2017; 14(3): 603-13.[http://dx.doi.org/10.1007/s10393-017-1239-8] [PMID: 28417211] ]. But an effect of the season was observed but only for rats captured in the parks. This suggests that seasonal fluctuations of the conditions for parasite survival and transmission may be reduced in the more human-dominated habitats like shantytowns.

CONCLUSION

To conclude, although host identity is a strong predictor of the structure of helminth infracommunities (diversity, composition, core species) within an urban rodent assembly [11Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669] ], helminth infection rates are affected by external factors such as the type of environment, meteorological conditions and demographic parameters of the hosts. Particularly, parasites with intermediate hosts or free living larval stages in their life cycle are the most affected species. This information is relevant because it allows us to deepen the ecological dynamics of parasites in urban rodents and shows that environmental conditions are determinants for the persistence of urban helminth populations. The link between pathogens-rodent-environment is intimately connected, needing holistic approaches to address the prevention of zoonoses. Therefore, an improvement of the hygienic and environmental quality must be considered in any health program against urban zoonoses, particularly in shantytowns where social, economical and environmental conditions expose their inhabitants to a high risk of the so-called neglected diseases.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

Not applicable.

HUMAN AND ANIMAL RIGHTS

No animals/humans were used for studies that are the basis of this research.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

The authors wish to thank all the team of the Laboratorio de Ecología de Roedores Urbanos for their assistance during the field sampling. We are also grateful to Dra. Graciela Navone (CEPAVE-CONICET-La Plata-Argentina) for her help provided during helminth identification and her valuable comments on earlier versions of the manuscript. Financial support was provided by the University of Buenos Aires, Gobierno de la Ciudad de Buenos Aires and CONICET (Argentina).

REFERENCES

[1] Thompson RC. Parasite zoonoses and wildlife: One Health, spillover and human activity. Int J Parasitol 2013; 43(12-13): 1079-88.[http://dx.doi.org/10.1016/j.ijpara.2013.06.007] [PMID: 23892130]
[2] Hassell JM, Begon M, Ward MJ, Fèvre EM. Urbanization and disease emergence: Dynamics at the wildlife-livestock-human interface. Trends Ecol Evol (Amst) 2017; 32(1): 55-67.[http://dx.doi.org/10.1016/j.tree.2016.09.012] [PMID: 28029378]
[3] Mackenstedt U, Jenkins D, Romig T. The role of wildlife in the transmission of parasitic zoonoses in peri-urban and urban areas. Int J Parasitol Parasites Wildl 2015; 4(1): 71-9.[http://dx.doi.org/10.1016/j.ijppaw.2015.01.006] [PMID: 25830108]
[4] Neiderud CJ. How urbanization affects the epidemiology of emerging infectious diseases. Infect Ecol Epidemiol 2015; 5: 27060.[http://dx.doi.org/10.3402/iee.v5.27060] [PMID: 26112265]
[5] Morand S, Bordes F, Chen HW, et al. Global parasite and Rattus rodent invasions: The consequences for rodent-borne diseases. Integr Zool 2015; 10(5): 409-23.[http://dx.doi.org/10.1111/1749-4877.12143] [PMID: 26037785]
[6] Kosoy M, Khlyap L, Cosson JF, Morand S. Aboriginal and invasive rats of genus rattus as hosts of infectious agents. Vector Borne Zoonotic Dis 2015; 15(1): 3-12.[http://dx.doi.org/10.1089/vbz.2014.1629] [PMID: 25629775]
[7] Himsworth CG, Parsons KL, Jardine C, Patrick DM. Rats, cities, people, and pathogens: A systematic review and narrative synthesis of literature regarding the ecology of rat-associated zoonoses in urban centers. Vector Borne Zoonotic Dis 2013; 13(6): 349-59.[http://dx.doi.org/10.1089/vbz.2012.1195] [PMID: 23590323]
[8] Bordes F, Blasdell K, Morand S. Transmission ecology of rodent-borne diseases: New frontiers. Integr Zool 2015; 10(5): 424-35.[http://dx.doi.org/10.1111/1749-4877.12149] [PMID: 26176684]
[9] Cavia R, Cueto GR, Suárez OV. Changes in rodent communities according to the landscape structure in an urban ecosystem. Landsc Urban Plan 2009; 90: 11-9.[http://dx.doi.org/10.1016/j.landurbplan.2008.10.017]
[10] Hancke D, Suárez OV. Helminth diversity in synanthropic rodents from an urban ecosystem. EcoHealth 2017; 14(3): 603-13.[http://dx.doi.org/10.1007/s10393-017-1239-8] [PMID: 28417211]
[11] Hancke D, Suárez OV. Structure of parasite communities in urban environments: The case of helminths in synanthropic rodents. Folia Parasitologica 2018; 65(1): 2018-009.[http://dx.doi.org/10.14411/fp.2018.009] [PMID: 30183669]
[12] Froeschke G, Matthee S. Landscape characteristics influence helminth infestations in a peri-domestic rodent--implications for possible zoonotic disease. Parasit Vectors 2014; 7: 393.[http://dx.doi.org/10.1186/1756-3305-7-393] [PMID: 25159989]
[13] Lagrue C, Poulin R. Spatial covariation of local abundance among different parasite species: The effect of shared hosts. Parasitol Res 2015; 114(10): 3637-43.[http://dx.doi.org/10.1007/s00436-015-4590-0] [PMID: 26113509]
[14] United Nations. World Urbanization Prospects: The 2014 Revision 2014.
[15] Bush AO, Lafferty KD, Lotz JM, Shostak AW. Parasitology meets ecology on its own terms: Margolis et al. revisited. J Parasitol 1997; 83(4): 575-83.[http://dx.doi.org/10.2307/3284227] [PMID: 9267395]
[16] Anderson MJ. A new method for non-parametric multivariate analysis of variance. Austral Ecol 2001; 26: 32-46.
[17] Janovy J Jr, Clopton RE, Clopton DA, Snyder SD, Efting A, Krebs L. Species density distributions as null models for ecologically significant interactions of parasite species in an assemblage. Ecol Modell 1995; 77: 189-96.[http://dx.doi.org/10.1016/0304-3800(93)E0087-J]
[18] Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM. Mixed effects models and extensions in ecology with R 2009.[http://dx.doi.org/10.1007/978-0-387-87458-6]
[19] Wenger SJ, Freeman MC. Estimating species occurrence, abundance, and detection probability using zero-inflated distributions. Ecology 2008; 89(10): 2953-9.[http://dx.doi.org/10.1890/07-1127.1] [PMID: 18959332]
[20] R Development Core Team. R: A language and environment for statistical computing 2014. Available from: http://www.R-project.org/
[21] Oksanen AJ, Blanchet FG, Kindt R. Package ‘vegan’ version 2.5-2. 2018
[22] Maimone C, Fearon J, Jackman MS. Package ‘pscl.’ 2012.
[23] Hothorn T, Zeileis A, Farebrother RW, Cummins C, Millo G, Mitchell D. Package “lmtest” 2018.
[24] Hancke D, Suárez OV. Infection levels of the cestode Hymenolepis diminuta in rat populations from buenos aires, argentina. J Helminthol 2016; 90(2): 199-205.[http://dx.doi.org/10.1017/S0022149X15000164] [PMID: 25869333]
[25] Roberts LS, Janovy J. Foundations of Parasitology 8th ed. 8th ed.2009.
[26] Malheiros AF, Mathews PD, Lemos LMS, Braga GB, Shaw JJ. Prevalence of Hymenolepis nana in indigenous Tapirapé ethnic group from the brazilian amazon. Am J Biomed Res 2014; 2: 16-8.[http://dx.doi.org/10.12691/ajbr-2-2-1]
[27] Robinson WH. Urban insects and arachnids: A handbook of urban entomology 2015.
[28] Himsworth CG, Jardine CM, Parsons KL, Feng AYT, Patrick DM. The characteristics of wild rat (Rattus spp.) populations from an inner-city neighborhood with a focus on factors critical to the understanding of rat-associated zoonoses. PLoS One 2014; 9(3): e91654.[http://dx.doi.org/10.1371/journal.pone.0091654] [PMID: 24646877]
[29] Hancke D, Navone GT, Suárez OV. Endoparasite community of Rattus norvegicus captured in an urban area of Argentina. Helminthologia 2011; 48: 167-73.[http://dx.doi.org/10.2478/s11687-011-0025-3]
[30] Anderson RC. Nematode parasites of vertebrates: Their development and transmission 2000.[http://dx.doi.org/10.1079/9780851994215.0000]
[31] Arneberg P. Host population density and body mass as determinants of species richness in parasite communities: Comparative analyses of directly transmitted nematodes of mammals. Ecography 2002; 25: 88-94.[http://dx.doi.org/10.1034/j.1600-0587.2002.250110.x]
[32] Zain SNM, Behnke JM, Lewis JW. Helminth communities from two urban rat populations in Kuala Lumpur, Malaysia. Parasit Vectors 2012; 5: 1-23.[PMID: 22212459]

Endorsements



"Open access will revolutionize 21st century knowledge work and accelerate the diffusion of ideas and evidence that support just in time learning and the evolution of thinking in a number of disciplines."


Daniel Pesut
(Indiana University School of Nursing, USA)

"It is important that students and researchers from all over the world can have easy access to relevant, high-standard and timely scientific information. This is exactly what Open Access Journals provide and this is the reason why I support this endeavor."


Jacques Descotes
(Centre Antipoison-Centre de Pharmacovigilance, France)

"Publishing research articles is the key for future scientific progress. Open Access publishing is therefore of utmost importance for wider dissemination of information, and will help serving the best interest of the scientific community."


Patrice Talaga
(UCB S.A., Belgium)

"Open access journals are a novel concept in the medical literature. They offer accessible information to a wide variety of individuals, including physicians, medical students, clinical investigators, and the general public. They are an outstanding source of medical and scientific information."


Jeffrey M. Weinberg
(St. Luke's-Roosevelt Hospital Center, USA)

"Open access journals are extremely useful for graduate students, investigators and all other interested persons to read important scientific articles and subscribe scientific journals. Indeed, the research articles span a wide range of area and of high quality. This is specially a must for researchers belonging to institutions with limited library facility and funding to subscribe scientific journals."


Debomoy K. Lahiri
(Indiana University School of Medicine, USA)

"Open access journals represent a major break-through in publishing. They provide easy access to the latest research on a wide variety of issues. Relevant and timely articles are made available in a fraction of the time taken by more conventional publishers. Articles are of uniformly high quality and written by the world's leading authorities."


Robert Looney
(Naval Postgraduate School, USA)

"Open access journals have transformed the way scientific data is published and disseminated: particularly, whilst ensuring a high quality standard and transparency in the editorial process, they have increased the access to the scientific literature by those researchers that have limited library support or that are working on small budgets."


Richard Reithinger
(Westat, USA)

"Not only do open access journals greatly improve the access to high quality information for scientists in the developing world, it also provides extra exposure for our papers."


J. Ferwerda
(University of Oxford, UK)

"Open Access 'Chemistry' Journals allow the dissemination of knowledge at your finger tips without paying for the scientific content."


Sean L. Kitson
(Almac Sciences, Northern Ireland)

"In principle, all scientific journals should have open access, as should be science itself. Open access journals are very helpful for students, researchers and the general public including people from institutions which do not have library or cannot afford to subscribe scientific journals. The articles are high standard and cover a wide area."


Hubert Wolterbeek
(Delft University of Technology, The Netherlands)

"The widest possible diffusion of information is critical for the advancement of science. In this perspective, open access journals are instrumental in fostering researches and achievements."


Alessandro Laviano
(Sapienza - University of Rome, Italy)

"Open access journals are very useful for all scientists as they can have quick information in the different fields of science."


Philippe Hernigou
(Paris University, France)

"There are many scientists who can not afford the rather expensive subscriptions to scientific journals. Open access journals offer a good alternative for free access to good quality scientific information."


Fidel Toldrá
(Instituto de Agroquimica y Tecnologia de Alimentos, Spain)

"Open access journals have become a fundamental tool for students, researchers, patients and the general public. Many people from institutions which do not have library or cannot afford to subscribe scientific journals benefit of them on a daily basis. The articles are among the best and cover most scientific areas."


M. Bendandi
(University Clinic of Navarre, Spain)

"These journals provide researchers with a platform for rapid, open access scientific communication. The articles are of high quality and broad scope."


Peter Chiba
(University of Vienna, Austria)

"Open access journals are probably one of the most important contributions to promote and diffuse science worldwide."


Jaime Sampaio
(University of Trás-os-Montes e Alto Douro, Portugal)

"Open access journals make up a new and rather revolutionary way to scientific publication. This option opens several quite interesting possibilities to disseminate openly and freely new knowledge and even to facilitate interpersonal communication among scientists."


Eduardo A. Castro
(INIFTA, Argentina)

"Open access journals are freely available online throughout the world, for you to read, download, copy, distribute, and use. The articles published in the open access journals are high quality and cover a wide range of fields."


Kenji Hashimoto
(Chiba University, Japan)

"Open Access journals offer an innovative and efficient way of publication for academics and professionals in a wide range of disciplines. The papers published are of high quality after rigorous peer review and they are Indexed in: major international databases. I read Open Access journals to keep abreast of the recent development in my field of study."


Daniel Shek
(Chinese University of Hong Kong, Hong Kong)

"It is a modern trend for publishers to establish open access journals. Researchers, faculty members, and students will be greatly benefited by the new journals of Bentham Science Publishers Ltd. in this category."


Jih Ru Hwu
(National Central University, Taiwan)


Browse Contents



Advertisements


Webmaster Contact: info@benthamopen.com
Copyright © 2018 Bentham Open