Black rats are among the world’s most invasive rodent species and are responsible for considerable agricultural losses and risks to human health through zoonotic disease. In Puerto Rico, rats may also compete with the primary rabies reservoir (the small Indian mongoose) for baits during oral rabies vaccination (ORV) programs. We evaluated black rat population density and home range size on the Cabo Rojo National Wildlife Refuge, southwestern Puerto Rico. We fitted 10 rats with VHF transmitters and tracked them using radio telemetry for approximately 4 weeks. We entered locations into ArcGIS and obtained minimum convex polygon (MCP) home range estimates. We established two plots of 55 snap traps and performed removal for 5 consecutive days during January and July, to correspond roughly with wet and dry seasons for this region. To calculate abundance, we entered snap trap data using a removal model approach in Program MARK. We calculated the effective trapping area by creating a buffer around the trapping area based on the square root of mean home range estimate. We divided the abundance calculated in MARK by the effective trapping area to calculate the estimated population density. Mean MCP home range estimate was 0.28 ha (SE: 0.05, range: 0.07-0.50 ha). Population density estimates were 114.7 (SE: 201.80) and 19.3 (SE: 6.85) per ha for January and July, respectively. To reduce the potential for rat consumption of ORV baits, wildlife managers should consider conducting ORV activities in Puerto Rico during periods of lower rat abundance or density.

The small Indian mongoose is an invasive pest species and rabies reservoir in Puerto Rico and other islands in the Caribbean. In the United States and Europe, rabies in wild carnivores is largely controlled through oral rabies vaccination (ORV), but no ORV program for mongooses exists. The oral rabies vaccine currently licensed for use in wild carnivores in the United States has not been reported as immunogenic for mongooses. A mongoose-specific bait has been developed but field-based bait flavor preference trials have not been performed in Puerto Rico. We evaluated removal of egg-flavored (treatment) vs. unflavored (control), water-filled placebo ORV baits in a subtropical dry forest in southwestern Puerto Rico from 2014-2015. During six trials at four plots we distributed 350 baits (175 treatment and 175 control) and monitored baits for five days or until at least 50% of baits had been removed or were rendered unavailable to mongooses due to inundation by fire ants. The estimated overall probability of bait removal within five days was 85% (95% CI 75-91%) and 45% (95% CI 35-55%) for treatment and control baits, respectively. Removal rate estimates in the spring were 95% (95% CI 86-98%) and 63% (95% CI 49-76%) for treatment and control baits, respectively. Removal rate estimates in autumn were 68% (95% CI 58-77%) and 30% (95% CI 22-39%) for treatment and controls, respectively. Model estimates suggest that treatment and season were more influential on bait removal rates than diel period or experimental day, although bait removal rates were higher at night than during the day, suggesting non-target bait removal by nocturnal rodents. Our results suggest that egg-flavored baits were preferred by mongooses over unflavored baits. During operational ORV bait application, non-target bait removal should be taken into consideration when calculating bait application rates.

Rabies is a fatal viral zoonosis that is transmitted by bite contact with saliva of an infected animal. In the U.S., human deaths are rare, but each year over 5,000 rabid animals are reported and over 90% of cases are from wildlife. Multiple species of carnivores and bats are the primary sylvatic reservoirs in the U.S., and several variants circulate independently among these two taxonomic orders. Rabies prevention efforts led by USDA APHIS Wildlife Services using live recombinant vaccine baiting began in 1995 and currently target raccoons and canids, but the territory of the south-central skunk rabies virus variant has been expanding in recent years, leading to incursions into areas previously free of carnivore rabies. Colorado has been one such area, where multiple species of bats were the main rabies reservoir prior to 2007. By 2012, the number of rabid striped skunks exceeded rabid bats in Colorado. Larimer County and Weld County, in Northern Colorado, both witnessed skunk rabies epizootics starting in 2012 that have continued through 2013. Despite spillover events into raccoons, red foxes, companion animals, and livestock during 2012 and 2013, no other host species appears to support independent circulation of the south-central skunk variant in Northern Colorado. Virus isolation from salivary glands of rabid animals will help to quantify the likelihood for secondary transmission from spillover hosts and guide intervention strategies targeting wildlife. We describe the spatiotemporal pattern of the epizootic and predict likely areas of spread along the Front Range of Northern Colorado.

Our ability to infer unobservable disease-dynamic processes such as force of infection (infection hazard for susceptible hosts) has transformed our understanding of disease transmission mechanisms and capacity to predict disease dynamics. Conventional methods for inferring FOI estimate a time-averaged value and are based on population-level processes. Because many pathogens exhibit epidemic cycling and FOI is the result of processes acting across the scales of individuals and populations, a flexible framework that extends to epidemic dynamics and links within-host processes to FOI is needed. Specifically, within-host antibody kinetics in wildlife hosts can be short-lived and produce patterns that are repeatable across individuals, suggesting individual-level antibody concentrations could be used to infer time since infection and hence FOI. Using simulations and case studies (influenza A in lesser snow geese and Yersinia pestis in coyotes), we argue that with careful experimental and surveillance design, the population-level FOI signal can be recovered from individual-level antibody kinetics, despite substantial individual-level variation. In addition to improving inference, the cross-scale quantitative antibody approach we describe can reveal insights into drivers of individual-based variation in disease response, and the role of poorly understood processes such as secondary infections, in population-level dynamics of disease.

The COVID-19 pandemic highlights the substantial public health, economic, and societal consequences of virus spillover from a wildlife reservoir. Widespread human transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also presents a new set of challenges when considering viral spillover from people to naïve wildlife and other animal populations. The establishment of new wildlife reservoirs for SARS-CoV-2 would further complicate public health control measures and could lead to wildlife health and conservation impacts. Given the likely bat origin of SARS-CoV-2 and related beta-coronaviruses (β-CoVs), free-ranging bats are a key group of concern for spillover from humans back to wildlife. Here, we review the diversity and natural host range of β-CoVs in bats and examine the risk of humans inadvertently infecting free-ranging bats with SARS-CoV-2. Our review of the global distribution and host range of β-CoV evolutionary lineages suggests that 40+ species of temperate-zone North American bats could be immunologically naïve and susceptible to infection by SARS-CoV-2. We highlight an urgent need to proactively connect the wellbeing of human and wildlife health during the current pandemic and to implement new tools to continue wildlife research while avoiding potentially severe health and conservation impacts of SARS-CoV-2 "spilling back" into free-ranging bat populations.