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Origin of RHDV outbreaks in domestic rabbits

These are the results of an online survey that was set up in February 2017. The idea is to try to discover more about the current outbreak of Rabbit Haemorrhagic Disease (RHD) that is killing rabbits in the UK and abroad. More information about RHD can be found here It is hard to know how the disease is spread so the survey was set up to compile information from owners who have lost rabbits to RHD.  So far we have only had 50 responses and we would like more.  A link to the survey can be found here

SURVEY RESULTS up to September 20th  2017 (comments at the end of the results)

 50 responses:  46 from UK, 1 from Malta, 2 from Germany, from The Netherlands

 The type of rabbits that died is summarised below:

The housing of the rabbits is summarised below:

The diet of the rabbits in the outbreaks is summarised below:

NUMBER of LOSSES ATTRIBUTED TO RHD

Two responses didn't make sense

1 rabbit kept on its own died

owners with two rabbits only lost one of them

9 owners with two rabbits lost both of them

owners with 3 or 4 rabbits only lost one of them

owners with 4 rabbits lost 2 or 3 of them

3 owners with 4 rabbits lost all of them

No owners with more than 4 rabbits lost all of them

5 owners with 5-10 rabbits lost more than 1-5 of them

owners with more than 10 rabbits only lost 1 of them

11 owners with more than 10 rabbits (14-50) lost a proportion of their rabbits. Losses ranged from 10-84%. 

A rescue centre with 86 rabbits only lost one

A breeding establishment with 200 does lost 140adults and 1300 offspring

ESTABLISHMENT of DIAGNOSIS

CONFIRMED CASES

 

From PM signs, histopathology and PCR testing

1

From PM signs and PCR

8

Histopathology and PCR

3

From PCR on liver

12

TOTAL

24

UNCONFIRMED CASES

 

From PM signs

18

From histopathology

2

From clinical signs only- no histopathology or PCR

5

TOTAL

25

NUMBER OF CASES CONFIRMED BY PCR

24

STRAIN OF RHD IN CASES CONFIRMED BY PCR

RHD

1

RHDV2

23

 

VACCINATION STATUS OF CASES CONFIRMED BY PCR

Vaccinated against RHD and RHDV2 (e.g Filovac) within six months

4

Nobivac Myxo/RHD over a year ago and Filavac within last 6 months

1

Vaccinated against RHD and RHDV2 (e.g Filovac) 6-12 months ago

0

Vaccinated against RHD and RHDV2 (e.g Filovac) over 12 months ago

0

Vaccinated against RHD1 (Castorex)

1

Nobivac Myxo/RHD within last year

11

Nobivac Myxo/RHD over a year ago

4

Unvaccinated

3

 

DIET in 21 outbreaks confirmed as RHD or RHDV2

23/24 outbreaks occurred in rabbits that were fed on a commercial food (pellets, nuggets or muesli mix) of different brands

22/24 outbreaks occurred in rabbit fed on hay from a variety of sources

One outbreak occurred in a group of rabbits fed on pellets and no hay

21/24 outbreaks occurred in rabbits fed on vegetables/herbs from a variety of supermarkets

19/24 outbreaks occurred in rabbits fed on grass and wild plants

CONTACT with WILD PLANTS

12 outbreaks occurred in rabbits that grazed in the garden

7 outbreaks occurred in rabbits that were fed on forage collected locally

5 outbreaks occurred in rabbits that were not fed on grass or wild plants

CONTACT of CONFIRMED CASES with WILD RABBITS

10 cases had no wild rabbits close to where they lived

cases had wild rabbits over half a mile away

4 cases had wild rabbits within half a mile

3 cases had rabbit in next field

1 case had wild rabbits in the garden

1 didn’t answer

CONTACT of CONFIRMED CASES with OTHER PEOPLE'S RABBITS

11 outbreaks occurred in rabbits (or their companions) that had been to the vets in the month before death. 2 owners worked at a vets

1 outbreak occurred in a rabbit belonging to a petsitter that visited other people's houses

4 outbreaks occurred in rabbits that had contact with rescue centres. Either directly or because owners fostered rabbits or worked in rescue.

1 outbreak occurred in a rabbit whose companion had been to a boarding establishment

7 outbreaks occurred in rabbits that had no contact at all with other people's rabbits but one of these occurred in rabbits that lived next to a premises that had had an outbreak of RHD

CONTACT of BOTH CONFIRMED AND UNCONFIRMED CASES with OTHER PEOPLE'S RABBITS

OWNERS IDEAS OF HOW THEIR RABBIT(S) MAY HAVE CAUGHT RHD IN CONFIRMED AND UNCONFIRMED CASES

24 owners had no idea where it could have come from

2 thought it had come from local wild rabbits

2 thought infection could have come from vets or from rescue centre

4 thought infection came from vets

2 blamed urban foxes and crows

1 thought infection came from boarding

1 thought infection was introduced with a new rabbit

1 thought it was from wild rabbit that the cat caught

1 thought it was from frozen rabbit meat that was used to feed cats

1 thought it might have come from farm that her husband and dog worked  and go hunting on

1 blamed sandals she had worn on holiday where there were wild rabbits

thought infection must have spread from neighbouring premises

1 suggested rats

1 suggested insects

1 suggested hay

didn’t answer

COMMENTS 

 The percentage of rabbits that died in outbreaks of RHD seems to be very variable. No-one with more than four rabbits lost all of them although there are reports of 83% dying in some of the rabbit colonies. Of the 13 owners with a pair of rabbits, nine lost both of them

The source of infection is still not clear. 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, the health benefits of feeding hay, veg, forage and grass outweigh the risk of RHD.

Although no firm conclusions can be drawn from the data, there was contact with premises with other rabbits had taken place within the previous month in 70% of the confirmed cases. Veterinary premises were top of the list, with a quarter of the cases visiting veterinary  premises before they died. This is not surprising as this 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, which highlights the need for tight biosecurity and encouraging owners to vaccinate their rabbits. 

The results confirm that vaccination with Nobivac Myxo/RHD is not protective against RHDV2 although it is not clear if it has any effect in reducing losses.

Since August, there are three new reports of rabbits that were that were vaccinated against RHDV2 that succumbed to the disease. This brings the total up to six (i.e. a quarter of the confirmed cases). In August, the survey was amended to find out interval between vaccination and the rabbit dying so we have more information. Two rabbits (from separate owners) were vaccinated against RHDV2 within two weeks of dying. The third was vaccinated less than 6 months before dying.  In the cases that were reported up to August, one rabbit was vaccinated with Filovac on the day it died so it wasn't long enough for the vaccine to be effective. The interval between vaccination and succumbing to the disease is not known in the remaining two cases. These reports are worrying, but do not reflect the vast number of rabbits that have been saved by the vaccine. Even if  vaccination is not 100% protective, it is better than no vaccination at all. RHDV2 is a horrible disease and vaccination is the only weapon we have. More information may come to light as a result of the Sudden or Unexpected Death investigation that has recently been extended to include PCR tests on liver samples from all rabbits that die suddenly or unexpectedly, not just those with histopathological evidence of RHD. 

No pattern is emerging on the brands of food, supermarkets or hay suppliers

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 wasn't 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 can’t take the answers out so this respondent’s data is included in graphs but is excluded from rest of report.