Evaluation of noninvasive molecular monitoring for fecal pathogens among free-ranging carnivores
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Date
2008-12-07
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Abstract
Disease surveillance in wildlife is limited by difficulties in obtaining ante-mortem diagnostic samples. Serologic surveys provide imperfect, retrospective measures of susceptible and immune subpopulations to pathogens that do not reveal which individuals are currently infectious. I examined fecal polymerase chain reaction (PCR) diagnostics as a noninvasive, alternative means of monitoring for pathogen presence among sympatric carnivores.
PCR assays were evaluated for canine distemper virus (CDV) and canine
parvovirus 2 (CPV2) by inoculating control feces with vaccines. Detection limits were below concentrations reported in clinically ill animals. The CPV2 assay amplified product from canine and feline vaccine strains while the CDV assay amplified 3 vaccine strains and neither cross-reacted with other vaccine viruses. Successful amplification, after 1 year, depended on the storage method and was robust in feces exposed to field conditions up to 2 to 3 weeks.
Simulated infection, involving modified-live vaccination, investigated fecal virus shedding. Coyote pups shed CPV2 in their feces by Day 7 post-vaccination at levels below antigen-capture enzyme-linked immunosorbent assay (ELISA) sensitivity. Virus shedding ceased by Day 14 post-vaccination. Evaluation of vaccine-induced fecal shedding of CDV was complicated by co-amplification of bacterial contaminants; however, no virus was detected in the conjunctival epithelium on Day 7. Field viruses amplified from feces of animals showing clinical disease.
Serologic and fecal PCR assays were deployed in eastern North Carolina where
free-ranging bears, bobcats, gray foxes, raccoons, coyotes, and red wolves coexist and
the viruses are endemic. All species had evidence of natural exposure to CDV and
individuals of 5 species were actively shedding virus. Exposure to CPV2-like viruses occurred in 5 species, although overall fecal shedding of the virus was rare. Virus shedding occurred in both seropositive and seronegative individuals.
Fecal PCR informs infectious disease models beyond the capabilities of serologic
surveys. Identification of infected individuals, population density estimates, and spatial
distributions allows more accurate estimation of contact rates within, and between,
susceptible host populations, and thus, supports better understanding of disease ecology for multi-host pathogens.
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Keywords
serology, wildlife, feces, disease ecology, ecosystem health, PCR
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Degree
PhD
Discipline
Comparative Biomedical Sciences
