Tag: Vaccination

  • Occupational hazards

    Occupational hazards

    Before I started vet school, I attended a workshop for aspiring vets where students shared anecdotes about the various occupational ailments they had experienced or witnessed over the years.

    Despite having to defer the start my veterinary degree due to a horse-related incident, I got through university largely unscathed by veterinary-related disease. I contracted a skin infection while on placement in Bolivia, but I don’t think that was anything zoonotic.

    However, some colleagues were not so lucky…

    Illnesses and injuries

    The various vet-student ailments that have affected friends include:

    • rotavirus caught while on a dairy EMS placement
    • an odd reaction to the BCG vaccine we received en masse in the first few weeks of vet school – after investigating a persistent cough, it transpired it was actually latent tuberculosis that would flare up periodically
    • a mumps epidemic – while not zoonotic, the disease spread like wildfire through those who attended “Vetski” one year (a number of other skiing-related injuries were suffered on the same trip, including two damaged knees)
    • the notorious cryptosporidiosis, which claimed at least one victim on every farm rotation group
    • ringworm – despite having been in close proximity to cattle heavily infected with ringworm, I have avoided it thus far (the same cannot be said for one friend, who had to claim she had thrush to convince the pharmacist to sell her the necessary antifungal cream)

    Appreciating dangers

    TB testing
    TB testing – one of the most dangerous veterinary tasks.

    Since qualifying, a good proportion of my work in practice has consisted of one of the most dangerous veterinary tasks – TB testing.

    While I remained relatively unharmed for the first few months, I did appreciate how easy it could be to get injured, with some dodgy crushes to contend with and, often, largely unhandled beasts.

    Having tested hundreds of cattle unscathed, my final test was quite eventful…

    During a previous test at this particular farm, the vet had considered sedating one of the cows because it was so wild – but this time I was prepared, with sedation at the ready in case it was needed and the crush chained so the cow couldn’t go flying out the front door.

    Crushed crush

    Although a great deal of jumping about took place, I managed to test the cow without needing to resort to xylazine. However, the bull, which could barely squeeze into the crush, decided to stick his head under the front door and bend it nearly in half as the farmer, his son and I watched in horror.

    Luckily, the bull seemed to think better of this plan and retreated before destroying the crush.

    After the farmer had bashed the door back into some resemblance of its original shape, one calf somehow jumped out of the side of the crush and ended in a neighbour’s field.

    First-hand experience

    Just as we thought we’d had enough entertainment for one day, one of the six-month-old sucklers managed to squash my hand between it and the crush.

    The world went green for a moment and I had to park myself on an upturned bucket.

    Having taken a bit of a breather, we got the next calf in and I tried to continue, but the world kept spinning and I didn’t want to take my glove off to look at the damage. Feeling highly embarrassed, I sat back down and telephoned the practice for backup while the farmer went off to fetch a cup of sugary tea.

    Not the only ones

    An x-ray thankfully found no breaks, but a lot of swelling and bruising.

    I joked with my doctor about occupational injuries, saying I didn’t suppose GPs would be likely to get into that kind of situation. However, he said he’d had a couple of knives pulled on him – one from someone demanding a prescription!

    So, maybe we’re not the only medical profession at such a high risk of injury, we’re just exposed to slightly different dangers.

  • SNAP FeLV antigen/FIV antibody test

    SNAP FeLV antigen/FIV antibody test

    The past decade has seen a significant shift in the prevalence of both FeLV and FIV in most European countries. This, coupled with a better understanding of the viral dynamics of FeLV, will influence the interpretation of the results of in-house diagnostics tests of these viral infections.

    FeLV is an RNA virus that undergoes classic retroviral replication that incorporates its own genes into the host genome, known as provirus. Of those infected, approximately 30% to 40% will not be able to mount an effective immune response and will become persistently viraemic (“progressors”).

    The SNAP FeLV antigen/FIV antibody test.
    The SNAP FeLV antigen/FIV antibody test.

    These cats will have a high proviral load, remain persistently antigen-positive and eventually succumb to the disease. These cats have a poor prognosis, with 70% to 90% succumbing to the disease within 18 to 36 months.

    The remaining infected cats will become “regressors”. These cats will be able to mount an effective immune response and, eventually, become antigen-negative; however, will still be provirus-positive as these cannot be completely eliminated.

    In extremely unusual circumstances, these cats may recrudesce and become viraemic again later in life – previously known as “latent” infection – but these cases are extremely rare. Cancer and corticosteroid-induced immunosuppression is thought to be responsible in these cases.

    FeLV prevalence

    The prevalence of FeLV is now much lower compared to 10 to 15 years ago, with successful culling and selective breeding programmes meaning the risk of false positive results is increased.

    A positive result could be because it is a true positive (FeLV-associated disease), transient positive or false positive. A much higher chance exists of a true positive within at-risk groups – young cats with lymphoma, anaemia or leukopenia, and cats with unusual infection or unexplained wasting diseases.

    A positive result in healthy cats should be considered suspicious. These cats could be regressors and should be retested 12 weeks later, where the result should become negative. Alternatively, it could be a false positive and an external lab should be used to confirm infection, preferably using an alternative method – such as DNA PCR – to test for the presence of provirus.

    FIV prevalence

    The interpretation of FIV test results, both in light of new disease prevalence data as well as epidemiological evidence, needs to be revised.

    The prevalence of FIV in Australia is a lot higher than previously thought. In a study based on cats from the inner Sydney area, the prevalence of FIV is 16% in domestic cats with outdoor access, 21% to 25% in two feral cat colonies and up to 32% among some populations of “sick” cats (Norris et al, 2007). An owner survey revealed almost 80% of Australian cats spend some time outdoors, posing most cats at a high risk of FIV exposure.

    Although no current statistics exist on the percentage of cats vaccinated for FIV, an increased vaccination rate will have a significant impact on the reliability on the results from in-house tests.

    Combination test

    As the name suggests, the SNAP combination FeLV antigen/FIV antibody test detects the presence of FIV antibodies. This test cannot distinguish antibodies from those naturally infected, vaccinated or derived from maternal antibody. To add to the confusion, antibodies can take anywhere between two to four weeks – and sometimes up to six months – to develop after initial infection.

    To overcome this problem, PCR is needed to determine the presence of viral RNA (ELISA-positive, PCR-negative).

    It should be noted the presence of FIV antibodies in naturally infected individuals is only indicative of a persistent infection. It is not correlated with the presence of immunodeficiency or diseases directly related to FIV. In fact, new epidemiological evidence shows FIV infection does not cause illness in most cats and does not seem to cause reduced lifespans.

    Summary

    Any cat having a FeLV-positive SNAP test result is considered to be actively shedding virus, regardless of its health status. A cat that has a FeLV-negative SNAP test means it is not viraemic, thus not shedding virus, but does not necessarily mean it is free from infection.

    On the other hand, the true FIV status of a cat remains difficult to determine in-house. A positive result could mean persistently infected, maternal antibody, vaccine-induced antibody or a false positive, whereas a negative result could mean true negative, early infection or false negative.

    Regardless of the result, the true relevance of the FIV status in the acute management of an otherwise healthy cat is questionable, considering the new epidemiological findings.