Speak of the devil: Salmonella strikes again
This past week proved to be an eventful one. Following last week’s article about Salmonella, we had a client with an outbreak of Salmonellosis.
It is rather scary when it happens, and all the questions are asked over and over. What causes it, where does it come from, how does it spread, and what can I do now? Salmonella organisms (and there are hundreds of types) are worldwide. They infect and cause disease in humans and basically any type of animal that you can think of.
I find this frightening. Mice and rats on a farm can be a reservoir of Salmonella, and birds like gulls and pigeons have been implicated in the spread of the disease.
Across all species, most at risk are those with a compromised immune system, like the young, the old, the sick, the pregnant etc. The most common symptom is diarrhoea, but if it crosses out of the gut, we can have arthritis, meningitis, dry gangrene, pneumonia, or the major scourge of an abortion storm.
Following treatment, clinical signs disappear (clinical cure), but the bacteria are often hiding out in the gallbladder, lymph nodes or tonsils, so we don’t have a bacteriological cure. Generally, calves do not become carriers, but all adult cattle become carriers for up to ten weeks, with some adults shedding Salmonella bacteria for years after some form of stress like calving, drying-off, drought, transportation, a period of poor nutrition, or parasite infection (particularly fluke). As I said here last week, the most common means of spread is by the faeco-oral route, through the mouth. Salmonella is passed on through milk, eggs, birth fluids, but most typically through faeces.
Poor hygiene or dirty conditions increase this spread. Infections with Salmonella in food-producing animals present a serious public health concern. Because Salmonella is a zoonotic disease, it can easily spread from your animals to you or your family.
If you have had an outbreak, you realise the importance of strict hygiene on the farm. No doubt, you are still vaccinating against Salmonella. If you have stopped, I urge you to start again. With a vast amount of potential reservoirs of infection on all farms, it is imperative to give your livestock protection. The vaccine produces antibodies in the vaccinated animal. If this animal gives birth shortly after, the colostrum will contain antibodies to protect the new born calf.
If starting a vaccination programme, because of an outbreak, you should isolate and treat clinically affected animals, and vaccinate the rest.
The isolated animals should be started on the vaccination programme when they recover. A small number of individuals may not respond to vaccination, due to immunological incompetence or some other reason, like a poor nutritional status. The initial course of the vaccine is two doses under the skin, as aseptically as possible, at least 21 days apart. If the cow or heifer has not calved within eight weeks of the second shot, the manufacturer recommends a third shot three to four weeks before calving, to boost antibodies in the colostrum, and to give extra protection around the stressful time of calving.
For best possible response, it is recommended not to give any other vaccines within 14 days before or after the Salmonella vaccine.
It is also recommended to re-vaccinate all stock prior to any period of stress, and at least within every 12 months.