Saturday 1st December 2018
A cautionary tale: Caprine Arthritis Encephalitis in goats!!
At the start of last month we had some rather devastating news: Coriander, our 18 month old Anglo Nubian goat returned a positive result for CAE. For those of you who may not know, CAE stands for Caprine Arthritis Encephalitis - it is a contagious viral infection, typically passed to a kid via its mother's milk but also through bodily secretions including blood and faces. The Encephalitis part affects the kids who, if affected, die in their first few months; the Arthritis part affects adults who may not show any symptoms for a while but when they do, they can be acute.
Like many viruses, animals can be affected and show no symptoms for years and they may carry it but not test positive for years either. Once an animal has it, there is no cure and despite having the potential to live without symptons for some considerable time, the only real option is to cull. The economic impact of having CAE in a commercial milking/meat herd can be enormous!
In this country CAE is not rife but it exists and this year the British Goat Vet Society have reported an increase in the number of positive results. Some goat keepers are part of the CAE Accreditation scheme, administered by SAC (Scottish Agricultural College) and they undertake to abide by a strict set of critiria to keep CAE out of their herds. Such criteria includes a 3m boundary between their goats and all other animals, non admission of any untested animals onto their land and their own regular testing. Some keepers, such as myself, undertake yearly testing, usually just before mating. Many owners of stud animals won’t allow their males to mate with anything that is not CAE negative. As with other such tests, results are given as a percentage: 0-50% being negative, 51-59% inconclusive and 60% and over as positive!
Coriander's result was 67% (!!!) which came, I can tell you, as one helluva shock!! However, both my vet and the vet I spoke to at SAC (once she has been appraised of my herd history), felt this ‘could’ be a rare false positive and that a retest was definitely the way forward. This was great to hear but didn’t stop days/ weeks of worry and heart ache and guilt!!!
So, why might this have been be a false positive?? Well firstly, Coriander's mum Sorrel had tested negative 2 years running and she was Coriander’s most likely source of infection (although against this was the fact that as already stated, goats can carry the disease but initially not test positive for it!). In addition, our other three goats were also negative and in the case of two of them, had, like Coriander's mum been negative two years running, with the third, Coriander’s brother, only been tested for the first time this year (due to being a youngster still). Then there was our bio-security: the only other goat that had come onto our land in the two years we have lived here was also CAE negative, we are also not near any other goats and animal movements on and off our land are generally quite limited!!
Against us however, was the fact we have sheep who can carry a very similar virus called Maedi Visna (MV) and they are not tested so ‘could’ be a possible source (albeit a very improbable one). Secondly, false negatives are quite rare: the CAE test has a test sensitivity of 98.4% and specificity of 99.3%.
Nonetheless, we were advised to do a retest. There were 2 reasons for this, one was that a genuine error ‘may’ have been made and the second was that in some rare circumstances, a goat may have antibodies in his/her system that are unrelated to CAE but give a positive reading! The retest had to be done three weeks after the first one and so we had an agonizing wait, compounded by the fact that whilst the first test results came back after 4 days, we had to wait 2 weeks for the second results, giving us a very long extra week to wait.
Despite the 'positive' slant on all this from the vets (isn’t it irritating that the word ‘positive’ can have such two highly contrasting meanings) it was hard to spend time with the goats every day knowing that we may need to cull Coriander and possibly her mum too. Just as hard was wondering how on earth we would break the news to the friend we had sold four kids to this summer, two of which were from the same mum as Coriander! We played a lot of mind games in that time!!
And then the phone call came, on a Monday morning!! And the result: a whopping THREE PERCENT!! 3% being about as negative as it can get. The relief was enormous, even our vet (not prone to displays of emotion) sounded a little overwhelmed!!
After the phone call I headed straight out to the goat barn to have words with Coriander and her 'antibodies', and I told her quite firmly, never, ever to put us through that again!!!
In this country CAE is not rife but it exists and this year the British Goat Vet Society have reported an increase in the number of positive results. Some goat keepers are part of the CAE Accreditation scheme, administered by SAC (Scottish Agricultural College) and they undertake to abide by a strict set of critiria to keep CAE out of their herds. Such criteria includes a 3m boundary between their goats and all other animals, non admission of any untested animals onto their land and their own regular testing. Some keepers, such as myself, undertake yearly testing, usually just before mating. Many owners of stud animals won’t allow their males to mate with anything that is not CAE negative. As with other such tests, results are given as a percentage: 0-50% being negative, 51-59% inconclusive and 60% and over as positive!
Coriander's result was 67% (!!!) which came, I can tell you, as one helluva shock!! However, both my vet and the vet I spoke to at SAC (once she has been appraised of my herd history), felt this ‘could’ be a rare false positive and that a retest was definitely the way forward. This was great to hear but didn’t stop days/ weeks of worry and heart ache and guilt!!!
So, why might this have been be a false positive?? Well firstly, Coriander's mum Sorrel had tested negative 2 years running and she was Coriander’s most likely source of infection (although against this was the fact that as already stated, goats can carry the disease but initially not test positive for it!). In addition, our other three goats were also negative and in the case of two of them, had, like Coriander's mum been negative two years running, with the third, Coriander’s brother, only been tested for the first time this year (due to being a youngster still). Then there was our bio-security: the only other goat that had come onto our land in the two years we have lived here was also CAE negative, we are also not near any other goats and animal movements on and off our land are generally quite limited!!
Against us however, was the fact we have sheep who can carry a very similar virus called Maedi Visna (MV) and they are not tested so ‘could’ be a possible source (albeit a very improbable one). Secondly, false negatives are quite rare: the CAE test has a test sensitivity of 98.4% and specificity of 99.3%.
Nonetheless, we were advised to do a retest. There were 2 reasons for this, one was that a genuine error ‘may’ have been made and the second was that in some rare circumstances, a goat may have antibodies in his/her system that are unrelated to CAE but give a positive reading! The retest had to be done three weeks after the first one and so we had an agonizing wait, compounded by the fact that whilst the first test results came back after 4 days, we had to wait 2 weeks for the second results, giving us a very long extra week to wait.
Despite the 'positive' slant on all this from the vets (isn’t it irritating that the word ‘positive’ can have such two highly contrasting meanings) it was hard to spend time with the goats every day knowing that we may need to cull Coriander and possibly her mum too. Just as hard was wondering how on earth we would break the news to the friend we had sold four kids to this summer, two of which were from the same mum as Coriander! We played a lot of mind games in that time!!
And then the phone call came, on a Monday morning!! And the result: a whopping THREE PERCENT!! 3% being about as negative as it can get. The relief was enormous, even our vet (not prone to displays of emotion) sounded a little overwhelmed!!
After the phone call I headed straight out to the goat barn to have words with Coriander and her 'antibodies', and I told her quite firmly, never, ever to put us through that again!!!