Infectious disease and red wolf conservation: assessment of disease occurrence and associated risks

MOLECULAR PREVALENCE OF SELECTED VECTOR-BORNE ORGANISMS IN CAPTIVE RED WOLVES (CANIS RUFUS)

The red wolf (Canis rufus) is a critically endangered North American canid, with surviving conspecifics divided between a captive breeding population and a reintroduced free-ranging population. The goal of this study was to assess the prevalence of selected vector-borne pathogens in captive red wolves. Whole blood samples were collected from 35 captive red wolves. Quantitative polymerase chain reaction (PCR) assays were performed on extracted DNA to identify infection by Trypanosoma cruzi and vector-borne organisms within the following genera: Anaplasma, Babesia, Bartonella, Ehrlichia, Mycoplasma, Neoehrlichia, Neorickettsia, and Rickettsia. All red wolves sampled were PCR-negative for all tested organisms. These pathogens are unlikely to constitute threats to red wolf conservation and breeding efforts under current captive management conditions. The results of this study establish a baseline that may facilitate ongoing disease monitoring in this species.

Sarcoptic mange severity is associated with reduced genomic variation and evidence of selection in Yellowstone National Park wolves (Canis lupus)

Population genetic theory posits that molecular variation buffers against disease risk. Although this "monoculture effect" is well supported in agricultural settings, its applicability to wildlife populations remains in question. In the present study, we examined the genomics underlying individual-level disease severity and population-level consequences of sarcoptic mange infection in a wild population of canids. Using gray wolves (Canis lupus) reintroduced to Yellowstone National Park (YNP) as our focal system, we leveraged 25 years of observational data and biobanked blood and tissue to genotype 76,859 loci in over 400 wolves. At the individual level, we reported an inverse relationship between host genomic variation and infection severity. We additionally identified 410 loci significantly associated with mange severity, with annotations related to inflammation, immunity, and skin barrier integrity and disorders. We contextualized results within environmental, demographic, and behavioral variables, and confirmed that genetic variation was predictive of infection severity. At the population level, we reported decreased genome-wide variation since the initial gray wolf reintroduction event and identified evidence of selection acting against alleles associated with mange infection severity. We concluded that genomic variation plays an important role in disease severity in YNP wolves. This role scales from individual to population levels, and includes patterns of genome-wide variation in support of the monoculture effect and specific loci associated with the complex mange phenotype. Results yielded system-specific insights, while also highlighting the relevance of genomic analyses to wildlife disease ecology, evolution, and conservation.

Dirofilaria immitis in wolves recolonizing northern Italy: are wolves competent hosts?

Background

Wild carnivores such as the grey wolf (Canis lupus), red fox (Vulpes vulpes) and golden jackal (Canis aureus) are recognized hosts of Dirofilaria immitis. However, few studies have focused on their actual role in the epidemiology of heartworm infection. This study describes the prevalence and distribution of D. immitis in wolves in a heartworm-endemic area in northern Italy where wolves have recently returned after long-time eradication, and investigates the fertility status of the collected adult nematodes.

Methods

In the frame of a long-term wolf monitoring programme in northwestern Italy, 210 wolf carcasses from four provinces were inspected for the presence of filarioid nematodes in the right heart and pulmonary arteries. Female heartworms were measured, and their uterine content analyzed according to a previously described “embryogram” technique.

Results

Three wolves, all originating from a single province (Alessandria), were positive for D. immitis (1.42%, 95% CI: 0.48–4.11%, in the whole study area; 13.6%, 95% CI: 4.7–33.3%, limited to the single province from which infected wolves originated). Mean intensity was 5 worms (range: 3–7) and the female worms measured 21–28 cm in length. Six out of 9 female worms harbored uterine microfilariae: 5 were classified as gravid; 1 showed a “discontinuous gradient”; and 3 were non-gravid.

Conclusions

The present data show that heartworm infection is already prevalent in wolves that have recolonized the known heartworm-endemic area. Based on “embryogram” results, wolves were shown suitable heartworm hosts. Interestingly, investigated wolves appeared similarly exposed to heartworm infection as sympatric unprotected dogs (owned dogs that have never received any heartworm prevention treatment) sampled at the beginning of the wolf return process.

Parasite-associated mortality in a long-lived mammal: Variation with host age, sex, and reproduction

Parasites can cause severe host morbidity and threaten survival. As parasites are generally aggregated within certain host demographics, they are likely to affect a small proportion of the entire population, with specific hosts being at particular risk. However, little is known as to whether increased host mortality from parasitic causes is experienced by specific host demographics. Outside of theoretical studies, there is a paucity of literature concerning dynamics of parasite-associated host mortality. Empirical evidence mainly focuses on short-lived hosts or model systems, with data lacking from long-lived wild or semi-wild vertebrate populations. We investigated parasite-associated mortality utilizing a multigenerational database of mortality, health, and reproductive data for over 4,000 semi-captive timber elephants (Elephas maximus), with known causes of death for mortality events. We determined variation in mortality according to a number of host traits that are commonly associated with variation in parasitism within mammals: age, sex, and reproductive investment in females. We found that potentially parasite-associated mortality varied significantly across elephant ages, with individuals at extremes of lifespan (young and old) at highest risk. Mortality probability was significantly higher for males across all ages. Female reproducers experienced a lower probability of potentially parasite-associated mortality than females who did not reproduce at any investigated time frame. Our results demonstrate increased potentially parasite-associated mortality within particular demographic groups. These groups (males, juveniles, elderly adults) have been identified in other studies as susceptible to parasitism, stressing the need for further work investigating links between infection and mortality. Furthermore, we show variation between reproductive and non-reproductive females, with mothers being less at risk of potentially parasite mortality than nonreproducers.