Diseases associated with translocation of captive cervids in North America

A review of chronic wasting disease (CWD) spread, surveillance, and control in the United States captive cervid industry

Chronic wasting disease (CWD) is a fatal prion disease of the family Cervidae that circulates in both wild and captive cervid populations. This disease threatens the health and economic viability of the captive cervid industry, which raises cervids in contained spaces for purposes such as hunting and breeding. Given the high transmissibility and long incubation period of CWD, the introduction and propagation of the infectious prion protein within and between captive cervid farms could be devastating to individual facilities and to the industry as a whole. Despite this risk, there does not yet exist a literature review that summarizes the scientific knowledge, to date, about CWD spread, surveillance, or control measures. Our review, which focused on peer reviewed, primary research conducted in the United States, sought to address this need by searching Google Scholar, Scopus, and Web of Science with a five-term keyword string containing terms related to the (1) location, (2) species affected, (3) disease, (4) captive cervid industry, and (5) topic of focus. Between the three databases, there were 190 articles that were selected for further examination. Those articles were then read to determine if they were about CWD spread, surveillance, and/or control in captive cervid facilities. The 22 articles that met these inclusion criteria were evaluated in detail and discussed, with recommendations for future collaborative work between captive cervid owners, government agencies, and researchers. This work will help to address, inform, and mitigate the rising problem of CWD spread and establishment.

Genetic analyses of the parasitic nematode, Parelaphostrongylus tenuis, in Missouri and Kentucky reveal unexpected levels of diversity and population differentiation

Wildlife translocations, which involve the introduction of naive hosts into new environments with novel pathogens, invariably pose an increased risk of disease. The meningeal worm Parelaphostrongylus tenuis is a nematode parasite of the white-tailed deer (Odocoileus virginianus), which serves as its primary host and rarely suffers adverse effects from infection. Attempts to restore elk (Cervus canadensis) to the eastern US have been hampered by disease caused by this parasite. Using DNA sequence data from mitochondrial and nuclear genes, we examined the hypothesis that elk translocated within the eastern US could be exposed to novel genetic variants of P. tenuis by detailing the genetic structure among P. tenuis taken from white-tailed deer and elk at a source (Kentucky) and a release site (Missouri). We found high levels of diversity at both mitochondrial and nuclear DNA in Missouri and Kentucky and a high level of differentiation between states. Our results highlight the importance of considering the potential for increased disease risk from exposure to novel strains of parasites in the decision-making process of a reintroduction or restoration.

Can genetic assignment tests provide insight on the influence of captive egression on the epizootiology of chronic wasting disease?

Identifying the sources of ongoing and novel disease outbreaks is critical for understanding the diffusion of epizootic diseases. Identifying infection sources is difficult when few physical differences separate individuals with different origins. Genetic assignment procedures show great promise for assessing transmission dynamics in such situations. Here, we use genetic assignment tests to determine the source of chronic wasting disease infections in free-ranging white-tailed deer (Odocoileus virginianus) populations. Natural dispersal is thought to facilitate the geographic diffusion of chronic wasting disease, but egression from captive cervid populations represents an alternative source of infection that is difficult to detect due to physical similarities with wild deer. Simulated reference populations were created based on allele frequencies from 1,912 empirical microsatellite genotypes collected in four sampling subregions and five captive facilities. These reference populations were used to assess the likelihood of ancestry and assignment of 1,861 free-ranging deer (1,834 noninfected and 27 infected) and 51 captive individuals to captive or wild populations. The ancestry (Q) and assignment scores (A) for free-ranging deer to wild populations were high (average Q wild = 0.913 and average A wild = 0.951, respectively), but varied among subregions (Q wild = 0.800-0.947, A wild = 0.857-0.976). These findings suggest that captive egression and admixture are rare, but risk may not be spatially uniform. Ancestry and assignment scores for two free-ranging deer with chronic wasting disease sampled in an area where chronic wasting disease was previously unobserved in free-ranging herds indicated a higher likelihood of assignment and proportion of ancestry attributable to captive populations. While we cannot directly assign these individuals to infected facilities, these findings suggest that rare egression events may influence the epizootiology of chronic wasting disease in free-ranging populations. Continued disease surveillance and genetic analyses may further elucidate the relative disease risk attributable to captive and wild sources.

Dealing in deadly pathogens: Taking stock of the legal trade in live wildlife and potential risks to human health

Zoonotic diseases cause millions of deaths every year. Diseases such as Ebola, severe acute respiratory syndrome (SARS), and avian influenza cause economic losses at the global level and jeopardize diplomatic relations between countries. As wildlife are the source of at least 70% of all emerging diseases and given the on-going concerns associated with wildlife trade as a disease transmission mechanism, we provide a 'global snapshot' of the legal trade in live wild animals and take stock of the potential health risks that it poses to global human health. Our analysis showed that 11,569,796 individual live wild animals, representing 1316 different species were exported from 189 different countries between 2012 and 2016. China was the largest exporter of live mammals (with 98,979 animals representing 58.7% of global trade). Nicaragua was the largest exporter of live amphibians (with 122,592 animals representing 53.8% of global trade). South Africa was the largest exporter of live birds (with 889,607 animals representing 39.2% of global trade). Peru was the largest exporter of live reptiles (with 1,675,490 animals representing 18.8% of global trade). Our analysis showed that mostly the USA and other high-income countries, the largest importers, drive the live animal trade. High-income countries and not the countries where wildlife diseases and pathogens are more likely to occur reported almost all of the disease reports to the World Organisation for Animal Health. Based on our findings, we discuss how maximising trade bans; working on human behaviour change and improving regulatory efforts to improve surveillance will decrease the risk of future pandemics, epidemics and outbreaks.

MOLECULAR DETECTION OF BABESIA ODOCOILEI IN WILD, FARMED, AND ZOO CERVIDS IN ONTARIO, CANADA

Babesia odocoilei, a tick-borne protozoan hemoparasite of white-tailed deer ( Odocoileus virginianus), is being increasingly recognized as a cause of disease in captive cervids in North America. Historically endemic in white-tailed deer, the natural wildlife reservoir in the southeastern US, B. odocoilei has been recently associated with hemolytic anemia in captive Eurasian tundra reindeer ( Rangifer tarandus tarandus), wapiti ( Cervus canadensis), and woodland caribou ( Rangifer tarandus caribou) in the northcentral and northeastern US and several Canadian provinces. The emergence of B. odocoilei is likely related to the northward expansion of the range of the tick vector, Ixodes scapularis, and possibly to cervid translocations. Following a disease outbreak in reindeer and wapiti at the Toronto Zoo in Ontario, Canada, we utilized a prospective postmortem survey to investigate the prevalence of B. odocoilei in wild, farmed, and zoo cervids in Ontario ( n=270) in 2016-18 by PCR and DNA sequencing of spleen samples. Zoo bovids have been suggested as potential hosts of B. odocoilei in zoos affected by cervid babesiosis, so we also collected postmortem samples from five species of bovids ( n=7) at the Toronto Zoo that died or were euthanized during this time. We detected B. odocoilei in 1% (2/142) of farmed red deer ( Cervus elaphus) as well as in 3% (1/29) of captive wapiti and 4% (3/68) of wild white-tailed deer. Tissues from all zoo bovids and caribou, zoo and wild moose ( Alces alces), and farmed white-tailed deer, wapiti-red deer hybrids, and fallow deer ( Dama dama), tested negative for B. odocoilei. No clinical cases of babesiosis were encountered during this study. These findings suggest that white-tailed deer are a potential natural wildlife reservoir for B. odocoilei in Ontario and that red deer and wapiti could serve as more-localized reservoirs.

Poor biosecurity could lead to disease outbreaks in animal populations

Human-mediated disease outbreaks due to poor biosecurity practices when processing animals in wild populations have been suspected. We tested whether not changing nitrile gloves between processing wood frog (Lithobates sylvaticus) tadpoles and co-housing individuals increased pathogen transmission and subsequent diseased-induced mortality caused by the emerging pathogen, ranavirus. We found that not changing gloves between processing infected and uninfected tadpoles resulted in transmission of ranavirus and increased the risk of mortality of uninfected tadpoles by 30X. Co-housing tadpoles for only 15 minutes with 10% of individuals infected resulted in ranavirus transmission and 50% mortality of uninfected tadpoles. More extreme mortality was observed when the co-housing infection prevalence was >10%. Our results illustrate that human-induced disease outbreaks due to poor biosecurity practices are possible in wild animal populations.