The length of time animals test positive for bluetongue, the rate of mortality in infected flocks and herds and whether animals can transmit the disease through breeding were some of the questions farmers in England received answers to on a recent webinar.
The webinar was hosted by the Agriculture and Horticulture Development Board (AHDB), with representatives from the Department of Environment, Food and Rural Affairs (DEFRA) and the Animal Plant Health Agency (APHA).
Q. What is the rate of mortality in flocks and herds where bluetongue has been confirmed?
Gordon Hickman of DEFRA said that the mortality rate has not been confirmed yet.
“It’s a really difficult one and I think we will soon be asking for more information from the collective community. We know what we know, which is the point in time that we did that clinical inspection and confirmed disease.
“What we haven’t got is a really good handle on how animals might have got infected subsequently, how many may have died subsequently. We will be doing follow-up work with those affected farms. It’s quite difficult to say whether they died of bluetongue or died of something else,” he said.
Sascha van Helvoort of the APHA said that many people will have heard about the high mortality rates in Holland.
For cattle, we think it’s due to other causes, not due to bluetongue, but in reality we haven’t had very high mortality
“I do think it’s different here in England at present. We are seeing mortality in sheep and that is due to bluetongue. For cattle, we think it’s due to other causes, not due to bluetongue, but in reality we haven’t had very high mortality.”
She said some animals with clinical signs are getting better, but that, equally, some are dying.
Hickman added that some animals have been euthanised on welfare grounds because of the clinical signs they are showing.
“Even if they don’t die, they have been euthanised on welfare grounds and I think it’s important to stress that,” he said.
Q: if an animal has contracted the virus, will it test positive for the rest of its life?The APHA official outlined that it is currently unknown how long an animal will stay positive for.
“It’s a really difficult one. We test for the virus itself and at some point that will be negative, but we also test for antibody reaction to the virus. It’s very unknown how long they stay positive to that, it could be years.
“There are still cases where we are detecting animals from the 2007-2008 period when we had [bluetongue serotype 8, BTV8], so there’s antibodies to that vaccine at the time and possibly they had a natural infection. The science is really unknown on that side of it.”
She said that while animals can test positive for antibodies, it does not mean that they are protected against this current strain of bluetongue (BTV3).
“If they are just positive for antibodies, it could mean either they were vaccinated with BTV8 at the time a long time ago or they’ve undergone disease in the past for BTV8 or they’ve currently, in the past season, been infected with BTV3,” she said.
Hickman said that from surveillance, a PCR-test signal can be picked up for at least five months.
“The guidance is that 60 days after that signal, those animals should be deemed to be not infectious, but you need to know when it was infected to count the 60 days back. We need to know if animals are vaccinated because they will definitely pick up anti-body from the vaccine,” he said.
Q: how possible is it for animals infected with bluetongue now to infect other animals in the spring at mating?
Animals do not infect each other, van Helvoort said.
“It is not a contagious disease, it is a disease spread by biting midges.
“What is obviously a risk are pregnant females who might have a calf in the springtime. When the dam is pregnant, when it’s bitten by an infected midge the calf could get infected inside the placenta, so when it’s born it could actually be an infected animal.
“Entire males are also a risk with their semen and germplasm; so embryos and frozen semen as well,” she said.
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The length of time animals test positive for bluetongue, the rate of mortality in infected flocks and herds and whether animals can transmit the disease through breeding were some of the questions farmers in England received answers to on a recent webinar.
The webinar was hosted by the Agriculture and Horticulture Development Board (AHDB), with representatives from the Department of Environment, Food and Rural Affairs (DEFRA) and the Animal Plant Health Agency (APHA).
Q. What is the rate of mortality in flocks and herds where bluetongue has been confirmed?
Gordon Hickman of DEFRA said that the mortality rate has not been confirmed yet.
“It’s a really difficult one and I think we will soon be asking for more information from the collective community. We know what we know, which is the point in time that we did that clinical inspection and confirmed disease.
“What we haven’t got is a really good handle on how animals might have got infected subsequently, how many may have died subsequently. We will be doing follow-up work with those affected farms. It’s quite difficult to say whether they died of bluetongue or died of something else,” he said.
Sascha van Helvoort of the APHA said that many people will have heard about the high mortality rates in Holland.
For cattle, we think it’s due to other causes, not due to bluetongue, but in reality we haven’t had very high mortality
“I do think it’s different here in England at present. We are seeing mortality in sheep and that is due to bluetongue. For cattle, we think it’s due to other causes, not due to bluetongue, but in reality we haven’t had very high mortality.”
She said some animals with clinical signs are getting better, but that, equally, some are dying.
Hickman added that some animals have been euthanised on welfare grounds because of the clinical signs they are showing.
“Even if they don’t die, they have been euthanised on welfare grounds and I think it’s important to stress that,” he said.
Q: if an animal has contracted the virus, will it test positive for the rest of its life?The APHA official outlined that it is currently unknown how long an animal will stay positive for.
“It’s a really difficult one. We test for the virus itself and at some point that will be negative, but we also test for antibody reaction to the virus. It’s very unknown how long they stay positive to that, it could be years.
“There are still cases where we are detecting animals from the 2007-2008 period when we had [bluetongue serotype 8, BTV8], so there’s antibodies to that vaccine at the time and possibly they had a natural infection. The science is really unknown on that side of it.”
She said that while animals can test positive for antibodies, it does not mean that they are protected against this current strain of bluetongue (BTV3).
“If they are just positive for antibodies, it could mean either they were vaccinated with BTV8 at the time a long time ago or they’ve undergone disease in the past for BTV8 or they’ve currently, in the past season, been infected with BTV3,” she said.
Hickman said that from surveillance, a PCR-test signal can be picked up for at least five months.
“The guidance is that 60 days after that signal, those animals should be deemed to be not infectious, but you need to know when it was infected to count the 60 days back. We need to know if animals are vaccinated because they will definitely pick up anti-body from the vaccine,” he said.
Q: how possible is it for animals infected with bluetongue now to infect other animals in the spring at mating?
Animals do not infect each other, van Helvoort said.
“It is not a contagious disease, it is a disease spread by biting midges.
“What is obviously a risk are pregnant females who might have a calf in the springtime. When the dam is pregnant, when it’s bitten by an infected midge the calf could get infected inside the placenta, so when it’s born it could actually be an infected animal.
“Entire males are also a risk with their semen and germplasm; so embryos and frozen semen as well,” she said.
Read more
Farming News: Bord Bia scheme changes, cattle trade and UK bluetongue update
England’s cattle farmers locked up by bluetongue
Bluetongue vaccines targeted at SE England
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