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Comments on results to January 2018

We now have data from 87 outbreaks of Rabbit Haemorrhagic Disease. A diagnosis of RHD was confirmed in 40 outbreaks either from histopathology of from PCR testing or both. Histopathology showing a typical pattern of acute hepatocellular necrosis of the liver. With one exception, the new variant of RHD (RHDV2) was detected in those cases that were confirmed by PCR testing, which suggests that RHDV2 is superseding the original variants of RHD as the cause of Rabbit Haemorrhagic Disease.

The mortality rate (i.e. the percentage of rabbits that die) in outbreaks of RHD seems to be very variable. It looks as if it may be increasing. In November’s report, no owner with more than four rabbits lost all of them. In this report, two owners with four rabbits and one owner with six rabbits lost all of them. No owners with more than ten rabbits lost all of them although there are reports of 83% dying in some of the rabbit colonies. Of the 34 owners with a pair of rabbits, 24 lost both of them.

The source of infection is still not clear. There are several ways that infection could be brought in from a rabbit that was ill or died from RHD. Wild rabbits are a reservoir of infection but they were not close to the 86 cases that we have data from.  Over one third of outbreaks occurred where no wild rabbits were close by. There was contact with other pet rabbits in approximately one third of all 86 reports. In the 40 confirmed cases of RHD, there was some contact with other rabbits, either directly or indirectly in 24 cases.  Contact occurred via companions or owners that worked in places where there were rabbits. Although vaccination against both RHD and RHDV2 is recommended for every rabbit, it is particularly important for rabbits that belong to people who work or help at a vets, rescue centre, pet shop or boarding establishment

Veterinary premises were top of the list of places that rabbits had visited before they died and where they could have become infected. This is not surprising as this it is where rabbits are taken when they are ill. It is not clear whether the rabbits caught the infection at the vets or were taken there because they were already ill. The role of carriers and stress induced flare-ups is not known. Four owners believed their rabbits had contracted the infection at the vets. It is not possible to eliminate the possibility of cross infection completely from veterinary premises but these results highlight the need for tight biosecurity and vaccination against RHDV2.

No pattern is emerging on the brands of food, supermarkets or hay suppliers. Owners obtained food for their rabbits from a variety of sources. No particular brand of food or supermarket chain stands out from the rest.

The majority of the rabbits that died were on a ‘good diet’ i.e. with hay, grass, vegetables and forage featuring heavily. All these foods could be contaminated by faeces of crow, foxes or other scavengers that feed on feed rabbits or even a carcase of a wild rabbit that died from the disease. Only one outbreak occurred in rabbits that were fed on pellets only. Despite these results, in my opinion, the health benefits of feeding hay, grass, vegetables and wild plants to rabbits outweigh the small risk of bringing in infection. Vaccination is the only reliable form of protection.

The results indicate that vaccination with Nobivac Myxo-RHD is not protective against RHDV2. About 60% of the outbreaks occurred in rabbits that were vaccinated with Nobivac Myxo-RHD. The results also suggest that vaccination against RHDV2 is not fully protective. 12/87 outbreaks occurred in rabbits that were vaccinated against RHDV2. Nine of these were among the 40 cases confirmed by histology or PCR.  However, four of these had been vaccinated within the last 2 weeks, which may not be not long enough for the vaccine to be fully protective.  Interestingly, the proportion of rabbits with RHD that were vaccinated against RHDV2 is higher in this survey than in the Sudden or Unexpected Death Survey. An interim report of the results is available here. 

There are several reasons why vaccinated rabbits can succumb to a disease they are vaccinated against. Firstly, the vaccine may not be 100% effective. In their datasheet, Filavac claims to be over 90% effective, not 100%. The health of the rabbit at the time of vaccination affects the success of vaccination. Rabbits that are already ill may not respond properly. The way the vaccine is transported, stored and administered is also important. The vaccine needs to be refrigerated and stored at the correct temperature. Multi dose vials need to be used within a few hours, which is a problem on premises with lots of rabbits. There must be a temptation to keep a partly used vial to vaccinate rabbits at a later date.

Some problems have emerged with the survey. For example, owners that have lost more than one rabbit with different vaccination statuses or diet have difficulties answering some of the questions accurately. The survey is only designed to try to gather and share information. It is not a scientific study so there is latitude with accuracy when filling it in. One respondent has lost no rabbits to RHD, which was not a helpful response. Although it was interesting to see that all their rabbits were OK with vaccination, we only want information from people who have lost rabbits to RHD.  I cannot take the answers out so this respondent’s data is included in graphs but is excluded from rest of report.