Disentangling the link between supplemental feeding, population density, and the prevalence of pathogens in urban stray cats

Background Supplemental feeding of free-roaming animals, including wildlife and feral or stray animals, is well known to have a substantial impact on various aspects of animal ecology including habitat use, activity patterns, and host-pathogen interactions. Among them, an increased population density (PD) of animals receiving supplemental food raises concerns regarding the transmission of pathogens in these host populations. The primary aim of this study was to investigate how supplemental feeding is associated with host PD and prevalence of pathogens with different transmission modes in urban stray cats. We hypothesized that supplemental feeding would be positively associated with host PD and the prevalence of pathogens with density-dependent transmission modes compared with pathogens with transmission modes that are considered relatively density-independent. Methods This study was conducted in six districts in Seoul, Republic of Korea which were selected based on different degrees of supplemental feeding and cat caretaker activity (CCA). The PD of stray cats was estimated by mark-recapture surveys. Stray cat blood samples (N = 302) were collected from stray cats by local animal hospitals from each district performing the trap-neuter-release which tested for eight pathogens with different transmission modes (feline immunodeficiency virus, feline leukemia virus (FeLV), feline panleukopenia virus, feline calicivirus, feline herpesvirus-1, Bartonella henselae, hemoplasma, and Toxoplasma gondii) with molecular or serological assays. Associations between the prevalence of each pathogen and PD, CCA, and sex of cats were statistically analyzed. Results In contrast to initial predictions, the cat PD was generally higher in low CCA districts. The prevalence of (FeLV), which is transmitted through direct contact, was significantly higher in areas with a high CCA, conforming to our hypothesis. On the other hand, the prevalence of feline parvovirus, which can be spread by environmental transmission, was higher in low CCA districts. The remaining six pathogens did not show any association with the CCA; however, they had a unique association with the PD or the sex of the stray cats. Discussion Our findings suggest that in addition to influencing the PD, supplemental feeding may affect the prevalence of pathogens in urban animals by mechanisms such as increased aggregation and/or altered foraging strategies, with different consequences depending on the transmission mode of each pathogen

Cutaneous Leishmaniasis in dogs: is high seroprevalence indicative of a reservoir role?

American cutaneous leishmaniasis (ACL) is a complex disease with a rich diversity of animal host species. This diversity imposes a challenge, since understanding ACL transmission requires the adequate identification of reservoir hosts, those species able to be a source of additional infections. In this study we present results from an ACL cross-sectional serological survey of 51 dogs (Canis familiaris), where we used diagnostic tests that measure dog\u27s exposure to Leishmania spp. parasites. We did our research in Panama, at a village that has undergone significant ecosystem level transformations. We found an ACL seroprevalence of 47% among dogs, and their exposure was positively associated with dog age and abundance of sand fly vectors in the houses of dog owners. Using mathematical models, which were fitted to data on the proportion of positive tests as function of dog age, we estimated a basic reproductive number (R0 ± s.e.) of 1・22 ± 0・09 that indicates the disease is endemically established in the dogs. Nevertheless, this information by itself is insufficient to incriminate dogs as ACL reservoirs, given the inability to find parasites (or their DNA) in seropositive dogs and previously reported failures to experimentally infect vectors feeding on dogs with ACL parasites

Survey of Wild Mammal Hosts of Cutaneous Leishmaniasis Parasites in Panama and Costa Rica

The eco-epidemiology of American cutaneous leishmaniasis (ACL) is driven by animal reservoir species that are a source of infection for sand flies that serve as vectors infecting humans with Leishmania spp parasites. The emergence and re-emergence of this disease across Latin America calls for further studies to identify reservoir species associated with enzootic transmission. Here, we present results from a survey of 52 individuals from 13 wild mammal species at endemic sites in Costa Rica and Panama where ACL mammal hosts have not been previously studied. For Leishmania spp. diagnostics we employed a novel PCR technique using blood samples collected on filter paper. We only found Leishmania spp parasites in one host, the two-toed sloth, Choloepus hoffmanni. Our findings add further support to the role of two-toed sloths as an important ACL reservoir in Central America

Risk factors associated with Trypanosoma cruziexposure in domestic dogs from a rural community in Panama

Chagas disease, caused by Trypanosoma cruzi infection, is a zoonosis of humans, wild and domestic mammals,including dogs. In Panama, the main T. cruzi vector is Rhodnius pallescens, a triatomine bug whose main naturalhabitat is the royal palm, Attalea butyracea. In this paper, we present results from three T. cruzi serological tests(immunochromatographic dipstick, indirect immunofluorescence and ELISA) performed in 51 dogs from 24 housesin Trinidad de Las Minas, western Panama. We found that nine dogs were seropositive (17.6% prevalence). Dogswere 1.6 times more likely to become T. cruzi seropositive with each year of age and 11.6 times if royal palms wherepresent in the peridomiciliary area of the dog’s household or its two nearest neighbours. Mouse-baited-adhesivetraps were employed to evaluate 12 peridomestic royal palms. All palms were found infested with R. pallescens withan average of 25.50 triatomines captured per palm. Of 35 adult bugs analysed, 88.6% showed protozoa flagellates intheir intestinal contents. In addition, dogs were five times more likely to be infected by the presence of an additionaldomestic animal species in the dog’s peridomiciliary environment. Our results suggest that interventions focused onroyal palms might reduce the exposure to T. cruzi infection

Host Life History Strategy, Species Diversity, and Habitat Influence Trypanosoma cruzi Vector Infection in Changing Landscapes

Background: Anthropogenic land use may influence transmission of multi-host vector-borne pathogens by changing diversity, relative abundance, and community composition of reservoir hosts. These reservoir hosts may have varying competence for vector-borne pathogens depending on species-specific characteristics, such as life history strategy. The objective of this study is to evaluate how anthropogenic land use change influences blood meal species composition and the effects of changing blood meal species composition on the parasite infection rate of the Chagas disease vector Rhodnius pallescens in Panama. Methodology/Principal Findings: R. pallescens vectors (N = 643) were collected in different habitat types across a gradient of anthropogenic disturbance. Blood meal species in DNA extracted from these vectors was identified in 243 (40.3%) vectors by amplification and sequencing of a vertebrate-specific fragment of the 12SrRNA gene, and T. cruzi vector infection was determined by pcr. Vector infection rate was significantly greater in deforested habitats as compared to contiguous forests. Forty-two different species of blood meal were identified in R. pallescens, and species composition of blood meals varied across habitat types. Mammals (88.3%) dominated R. pallescens blood meals. Xenarthrans (sloths and tamanduas) were the most frequently identified species in blood meals across all habitat types. A regression tree analysis indicated that blood meal species diversity, host life history strategy (measured as rmax, the maximum intrinsic rate of population increase), and habitat type (forest fragments and peridomiciliary sites) were important determinants of vector infection with T. cruzi. The mean intrinsic rate of increase and the skewness and variability of rmax were positively associated with higher vector infection rate at a site. Conclusions/Significance: In this study, anthropogenic landscape disturbance increased vector infection with T. cruzi, potentially by changing host community structure to favor hosts that are short-lived with high reproductive rates. Study results apply to potential environmental management strategies for Chagas disease

Null expectations for disease dynamics in shrinking habitat: dilution or amplification?

As biodiversity declines with anthropogenic land-use change, it is increasingly important to understand how changing biodiversity affects infectious disease risk. The dilution effect hypothesis, which points to decreases in biodiversity as critical to an increase in infection risk, has received considerable attention due to the allure of a win–win scenario for conservation and human well-being. Yet some empirical data suggest that the dilution effect is not a generalizable phenomenon. We explore the response of pathogen transmission dynamics to changes in biodiversity that are driven by habitat loss using an allometrically scaled multi-host model. With this model, we show that declining habitat, and thus declining biodiversity, can lead to either increasing or decreasing infectious-disease risk, measured as endemic prevalence. Whether larger habitats, and thus greater biodiversity, lead to a decrease (dilution effect) or increase (amplification effect) in infection prevalence depends upon the pathogen transmission mode and how host competence scales with body size. Dilution effects were detected for most frequency-transmitted pathogens and amplification effects were detected for density-dependent pathogens. Amplification effects were also observed over a particular range of habitat loss in frequency-dependent pathogens when we assumed that host competence was greatest in large-bodied species. By contrast, only amplification effects were observed for density-dependent pathogens; host competency only affected the magnitude of the effect. These models can be used to guide future empirical studies of biodiversity–disease relationships across gradients of habitat loss. The type of transmission, the relationship between host competence and community assembly, the identity of hosts contributing to transmission, and how transmission scales with area are essential factors to consider when elucidating the mechanisms driving disease risk in shrinking habitat. This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications'

Anthropogenic land use change and infectious diseases: a review of the evidence

Humans have altered ecosystems worldwide, and it is important to understand how this land use change impacts infectious disease transmission in humans and animals. We conducted a systematic review 305 scientific articles investigating how specific types of anthropogenic land use change influence infectious disease dynamics. We summarized findings, highlighted common themes, and drew attention to neglected areas of research. There was an increase in publications on this topic over the last 30 years spanning diseases of humans, livestock, and wildlife, including a large number of zoonotic pathogens. Most papers (66.9%) were observational, 30.8% were review or concept papers, and few studies (2.3%) were experimental in nature, with most studies focusing on vector-borne and/or multi-host pathogens. Common land use change types related to disease transmission were deforestation/forest fragmentation/habitat fragmentation, agricultural development/irrigation, and urbanization/suburbanization. In response to anthropogenic change, more than half of the studies (56.9%) documented increased pathogen transmission, 10.4% of studies observed decreased pathogen transmission, 30.4% had variable and complex pathogen responses, and 2.4% showed no detectable changes. Commonly reported mechanisms by which land use change altered infectious disease transmission included alteration of the vector, host, and pathogen niche, changes in host and vector community composition, changes in behavior or movement of vectors and/or hosts, altered spatial distribution of hosts and/or vectors, and socioeconomic factors, and environmental contamination. We discussed observed patterns in the literature and make suggestions for future research directions, emphasizing the importance of ecological and evolutionary theory to understand pathogen responses in changing landscapes