Davis Mountains Cottontail Population Status and Mitigation of Rabbit Hemorrhagic Disease Virus 2
Request for Proposals November 2023

Introduction

For species at risk of being impacted by an emerging disease, planning effective actions for conservation and disease-management requires information regarding the species’ population status and demography along with an understanding of the dynamics of the disease spread and how various strategies may mitigate its spread. The Davis Mountains cottontail (Sylvilagus robustus) is a species of greatest conservation need (SGCN) in Texas due to its restricted range, likely small population sizes, and threats from habitat loss and drought. However, much is unknown about the populations, and they may also be at risk of decline from rabbit hemorrhagic disease virus 2 (RHDV2). A better understanding of the species’ population dynamics and RHDV2 immunity afforded by vaccinating wild rabbits would benefit conservation for the Davis Mountains cottontail.

RHDV2, a variant of the RHDV1 calicivirus, was first detected in France in 2010. The disease can infect lagomorphs as young as 11 days old and causes a necrotizing hepatitis. The RHDV2 variant can infect more host lagomorph species than could RHDV1, including Lepus hare species and North American Sylvilagus species. This novel viral strain combined with naïve rabbit populations can lead to an around 90% mortality rate and has caused population declines of up to 80% in some wild rabbit populations (Delibes-Mateos et al. 2014, Lavazza et al. 2023). RHDV2 is highly virulent and easily transmissible among wild and domestic rabbits through direct or indirect contact. It can persist in the environment in infected carcasses, contaminated fecal matter, water, fomites, or insect vectors. Due to the extremely high mortality rate and potential to cause severe population declines, this disease poses a major threat to imperiled rabbit species; however, impacts on rabbit populations in the United States have not been well-studied.

The first confirmed cases of RHDV2 in wild rabbit populations in the United States occurred in New Mexico in 2020 and subsequently spread. Since 2020, RHDV2 cases have been confirmed in wild rabbits in 16 Texas counties. Although there have been no confirmed cases of RHDV2 in Davis Mountains cottontails in Texas as of summer 2023, the disease has been documented in other lagomorph species in the counties where the Davis Mountains cottontail occurs.

The Davis Mountains cottontail is generally found in pinon–oak–juniper woodlands at elevations above 1,800 meters. It is endemic to the high-elevation mountains in West Texas and neighboring mountains in New Mexico and Mexico, including the Guadalupe Mountains, Davis Mountains, Chisos Mountains, and Sierra Madre. Additional populations may exist in other high-elevation mountains in the region, but current distribution data is lacking from these ranges. A paucity of contemporary records from the Guadalupe Mountains in the last several decades indicate that the population on that mountain range may be extremely small or extirpated. Also, there are no current density/abundance estimates or data on population trends or other demographic parameters for the species on any of the mountain ranges.

Vaccination of domestic rabbits against RHDV1 and RHDV2 has been shown to reduce mortality rates (Bosco-Lauth 2022) and new methods are being explored for screening live animals for RHDV2 (Asin et al. 2023), both of which could be important considerations in a species’ monitoring and action plan for the disease. Vaccination of imperiled wild rabbit populations is occurring elsewhere, but no such efforts have occurred in Texas and many questions remain regarding the effectiveness of vaccinating wild rabbits. An RHDV2 monitoring and vaccination program could potentially aid in the conservation of the Davis Mountains cottontail; however, basic population information is needed for the species along with information on the effectiveness of vaccinating individuals. As such, Texas Parks and Wildlife Department (TPWD) seeks to better understand the current status and population dynamics of the Davis Mountains cottontail and seeks information to guide the development of a science-based plan for monitoring and mitigating impacts of RHDV2 on the species.

Justification

As an SGCN species, research and disease mitigation for the Davis Mountains cottontail are justified by the Texas Wildlife Action Plan/State Wildlife Action Plan. Additionally, this project addresses several strategies from the 2015 TPWD Land and Water Resources Conservation and Recreation Plan:

• Goal 1: Practice, encourage and enable science-based stewardship of natural and cultural resources.
  • TPWD will be an exemplary steward of the public’s lands and waters by using the best available science for ecosystem-based management.
    • Establish protocols to address invasive species, wildlife diseases and other threats to plants, fish and wildlife.
  • TPWD will protect and assist in the recovery of threatened, endangered and high-priority species.
    • Use the Texas Wildlife Action Plan as the guiding document for prioritizing agency actions to address species of greatest conservation need.

Research Objectives

The study design should address all of the following objectives:

1. Provide status information on Davis Mountains cottontail populations, including current distribution, population estimates, demographics, and population dynamics.
2. Investigate the effectiveness of a vaccination program for Davis Mountains cottontails (e.g., persistence of immunity from RHDV2 after vaccination, presence of maternal antibodies after vaccination, percentage of population to be vaccinated, etc.).
3. Build a model to project Davis Mountains cottontail populations into the future under various potential scenarios (e.g., RHDV2 impact on survival, vaccination, drought conditions, etc.).

Optional objectives:

4. Create a habitat suitability model for the Davis Mountains cottontail based on fine scale habitat selection.
5. Document the current distributional limits of desert cottontail (S. audubonii) and eastern cottontail (S. floridanus) in West Texas to verify the apparent sympatric or allopatric distribution of each species with the Davis Mountains cottontail.

All submitted research projects are expected to last 3 to 5 years in order to collect meaningful data given population boom and bust cycles. Additionally, for this RFP, we would like to ask proposals to include: (1) the standard, full budget for all proposed work, plus (2) a second breakout budget just for objectives 1 and 3 above (and optional objectives 4 and/or 5, if included), and (3) a third breakout budget just for objective 2. All three budgets would follow/use the provided Excel budget template. However, proposals should only refer to the full budget (budget # 1 above) in any parts of the written proposal where references to the proposal budget are required (i.e., do not reference the breakout budgets in the proposal text, just use the full budget for that).

Expected Management Implications

Resulting information on Davis Mountains cottontail populations and RHDV2 mitigation strategies from this project will help guide future monitoring and conservation efforts for the species. In this way, TPWD will be able to apply the best available science for the conservation of the Davis Mountains cottontail.

Supporting Literature

• Asin, Javier, et al. 2023. "An RT-qPCR Assay from Rectal Swabs for the Detection of Rabbit Hemorrhagic Disease Virus 2 in Natural Cases." Transboundary and Emerging Diseases 2023.
• Bosco-Lauth AM, Cominsky B, Porter S, Root JJ, Schueler A, Anderson G, VanderWal S, Benson A. 2022. A novel vaccine candidate against rabbit hemorrhagic disease virus 2 (RHDV2) confers protection in domestic rabbits. Am J Vet Res. 83(12):ajvr.22.05.0095. doi: 10.2460/ajvr.22.05.0095. PMID: 36327167.
• Delibes-Mateos, Miguel, et al. 2014. “Ecosystem effects of variant rabbit hemorrhagic disease virus, Iberian Peninsula.” Emerging Infectious Diseases 20.12: 2166.
• Lavazza, A., and L. Capucci. 2023. “Chapter 3.7.2 Rabbit haemorrhagic disease.” In World Organization for Animal Health manual of diagnostic tests and vaccines for terrestrial animals.