After a tough term of remote learning, a group of final year vet students are undertaking their last exams this week: best of luck to them all!
But it made me think about one exam question we always had to be ready for when I was a vet student: "what diseases are covered by 5-in-1 vaccine?".
It was always a struggle to remember the scientific names of the clostridial bacteria in question-Clostridium novyi, chauvoei, tetani, septicum and perfringens-and which disease of cattle and sheep they went with: Black Disease, Black Leg, Tetanus, Malignant Edema and Pulpy Kidney (aka Enterotoxemia).
Clostridia live in two forms, the first as active bacteria in the intestinal tract of animals.
But out in the environment-in faeces, soil, water, and dust-they form dormant spores, which enable them to survive for long periods of time; these spores can be ingested and transfer themselves to an animal's muscles and liver.
When tissue oxygen levels become low, such as with wounds or poor blood flow, these spores then activate and multiply.
The bacteria produce toxins that kill animals quickly, causing severe edema, tissue necrosis and gas gangrene along the way; they are nasty!
Malignant Edema (Clostridium septicum) occurs in wounds from castration, docking, shearing, and calving/lambing/kidding trauma.
In Black Disease, Clostridium novyi multiplies when the liver is damaged by migration of liver flukes.
Black leg (Clostridium chauvoei) can develop without any obvious wounds, though bruising or exercise can precipitate disease; as well as sudden death, clinical signs include depression, muscle swelling and crepitus and severe lameness.
Clostridium tetani, tetanus, is associated with contamination of deep wounds; the toxin from this bacterium causes muscle rigidity ("lock jaw" and a "sawhorse" stance) and animals die from respiratory paralysis.
Clostridial disease is also associated with overgrowth and toxin production by the normal bacteria of the intestines due to changes in diet.
There are several strains of Clostridium perfringens which are involved in a few such diseases: Pulpy Kidney, Focal Symmetrical Encephalomalacia (FSE), Jejunal Haemorrhagic Syndrome (JHS) and abomasitis.
Pulpy Kidney, FSE and JHS occur when Clostridium perfringens proliferates in the gut of animals grazing lush pasture or crops or who overeat grain or milk.
As well as sudden death, clinical signs range from stargazing and convulsions to abdominal pain and passing of blood clots in the faeces
Abomasitis is a seen in calves where whole milk is fortified with other additives, such milk replacer; this increases the total solids of the liquid diet and decreases oxygen content.
Signs include bloat, abdominal pain, and death; on post-mortem there is a gas-filled and inflamed abomasum.
Vaccination is the key to preventing clostridial diseases.
Young animals need an initial course of 2 vaccinations 4 to 6 weeks apart; ensure they are vaccinated prior to periods of risk (e.g. castration, shearing, lush pasture).
Booster vaccinations are given annually (or in the case of goats, 6 monthly); vaccination of dams in late pregnancy will help maximise antibodies in colostrum.
It's important to handle vaccines carefully - you don't want to waste them!
Check that your vaccine fridge is cool enough (2-8°C) but not freezing; don't overload it with product and avoid cooling large items such as buckets of colostrum.
On vaccination day, protect the vaccines from heat, sunlight, dirt, and dust - such as keeping them inside an esky; some products need to be used within 24 hours of opening while others can be kept for a period of time, provided they are handled hygienically and kept cool.
Avoid vaccination when animals are wet or dusty and do not administer vaccine through visibly contaminated skin.
Some vaccines are combined with selenium, Vitamin B12, a wormer, or vaccines for other diseases such as leptospirosis and cheesy gland; doses vary from 1 to 4 mL, depending on the product and animal species.
So always check the label directions (dose, frequency, injection site, withholding periods), particularly if you are changing to a product you haven't used before.
About the author: Dr Zoe Vogels is a veterinarian at The Vet Group, Timboon.
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