Sensible biosecurity measures should be employed
Photo credit R Sibbald

On the ever topical subject of RVHD2, we are frequently asked about the four month quarantine period that seems to be accepted. This advice did not come from the RWAF but in response to the questions regarding it we have released the following statement. It is not possible for the RWAF to issue blanket advice that covers all situations here as a lot will depend on the biosecurity and vaccination status of individual rescue centres for example. It is up to the rabbit owners to discuss this and agree what is best for them with their own vet. Sensible biosecurity measures should be employed

“Here at the RWAF we are getting a lot of questions about the survival of RVHD1 and 2 in the rabbit and the environment. There are a number of questions to answer, and the conditions in the wild vary, well, wildly. And also it’s good to have some safety margin, but it’s unhelpful to add a safety margin on top of an existing one, at each stage the issue is discussed!

“It’s very important to note that this is one of the few conditions in domestic pets where we have a large reservoir of infection in the wild, maintaining the disease and keeping it in play. This can make the idea of achieving “herd immunity” near impossible, and muddies the waters regarding whether an infection is a new outbreak from the same wild source, or re-infection in a group not given sufficient time for the virus to die away.

“This reference is interesting re survival in the wild population: https:// onlinelibrary.wiley.com/doi/full/10.1111/eva.12195, and contains some data relevant to our UK population, including that:

• The virus can survive for nine days in flies
• That whilst theoretically, rabbits who have survived infection can continue to spread it beyond the immediate period (i.e. that at times of stress they can start to shed virus again), in practice they could not make this happen
• The virus spreads at a minimum speed of 15 – 60km/week (too fast to simply be from rabbit to rabbit)
• It can cross 20 – 100km of water via birds or insects
• It can survive over the summer months before flaring up again (note that these are Australian summer months, and therefore much hotter and drier than the UK)
• Viable virus can persist for some months in tissues within a cool burrow (McColl et al. 2002; Henning et al. 2005).

“Another paper is probably the most useful: https://www.cambridge.org/core/journals/ epidemiology-and-infection/article/survival-of-rabbithaemorrhagic-disease-virus-rhdv-in-the-environment /0736D6857EE8B52C073F75989514CDD5.

The results of this study suggest that RVHD in animal tissues such as rabbit carcasses can survive for at least 3 months in the field, while virus exposed directly to environmental conditions, such as dried excreted virus, is viable for a period of less than one month. Survival of RVHD in the tissues of dead animals could, therefore, provide a persistent reservoir of virus, which could initiate new outbreaks of disease after extended delays.

“Another study showed that while viral antigen could be detected for at least 30 days post death in a decomposing liver, infectious RVHD virus survived for only 20 to 26 days (McColl, K; Morrissy, C; Collins, B; and Westbury, H. (2002), Persistence of Rabbit Haemorrhagic Disease virus in decomposing rabbit carcasses. Australian Veterinary Journal, 80: 298-299. doi: 10.1111/j.1751-0813.2002.tb10848.x).

“The eight month (225 days) figure reflects the longest it is possible for the virus to survive under optimal conditions i.e. held at 4C in a viral nutrient broth. This is a theoretical situation, but the experiment was stopped at 225 days, and so this longevity could be even longer in this situation (Rabbit Haemorrhagic Disease: an investigation of some properties of the virus and evaluation of an inactivated vaccine (Smid et al Veterinary Microbiology, 26 (1991) 77-85).

“A four month figure has been proposed in the UK and is widely used, probably consisting of three months plus a month for the delay from infection to death, and a safety margin on top”.