Question: I would like to know more about salmonella infections in cattle, because I have heard that humans can also be infected.
Salmonellosis in cattle is also known as paratyphoid. It causes diarrhoea and death in calves, as well as diarrhoea, death and abortions in cows.
Salmonellosis is caused by a bacterium, Salmonella enterica, but in South Africa salmonellosis is caused mainly by 2 serovars (types) of Salmonella enterica, namely Salmonella Typhimurium and Salmonella Dublin.
- There are many different serovars of salmonella, but these 2 types occur most often.
- Salmonella Dublin occurs specifically in cattle, but Salmonella Typhimurium can make most mammal species sick, including humans. It is, therefore, considered to be an important zoonosis.
- S. Typhimurium affects young calves between the ages of 1 and 4 weeks.
- S. Dublin mainly affects calves 1 to 4 months old.
- Paratyphoid is more common in calves between the ages of 3 weeks and 3 months, but may affect cattle of any age.
- In fact, salmonellosis is increasingly becoming an important cause of diseases and abortions in cows.
- It is also more common in dairy cows than in beef cattle, mainly as a result of the intensive management and stress, which also place cattle in feedlots in a higher risk category.
- It is interesting that salmonellosis is often not diagnosed in feedlots, because of the perception that the disease only occurs in dairy calves.
Salmonella could infect calves of any age resulting in a variety of different disease syndromes, varying from sudden death in the absence of any preliminary signs of disease, to a low-grade chronic infection that has few clinical signs, apart from weight loss and a generally poor performance.
The most common disease syndrome encountered is one in which there is:
- A high temperature (above 39.6%).
- Refusal to eat or drink.
- Putty-like, progressive diarrhoea having an offensive odour and containing lots of mucous and possibly blood.
- Rapid breathing.
- A watery nasal discharge.
- A light cough that may persist for weeks while the calf is recovering from the disease.
Salmonellosis in cows may present the same disease syndromes as in calves (fever and diarrhoea), but it is also an important cause of abortion, either before of after the diarrhoea occurs.
- About 70% of the cows that abort because of salmonellosis have retained afterbirths.
- The mortality rate in cows may at times be as high as 50%.
- If they survive the disease, it may take as long as 2 to 3 months for complete recovery to occur.
- Then they remain carriers and spread the disease.
DIAGNOSIS AND TREATMENT
It is important to diagnose salmonellosis at an early stage in the course of the disease. Obtain the help of a veterinarian who, with laboratory assistance, is able to diagnose the disease.
It is extremely important to differentiate between infections caused by S. Typhimurium and S. Dublin, as each has a different course, and the treatment, prevention and measures for combatting them differ considerably.
- Do not simply assume that a calf has paratyphoid if a foul-smelling, putty-like diarrhoea is present.
- An incorrect diagnosis could lead to great losses and the unnecessary use of inappropriate antibiotics.
- Antibiotics such as neomycin, ampicillin, tetracycline, penicillin and streptomycin should not be used to treat paratyphoid.
- These substances are, in general, ineffective against salmonella infections, but they are often used to treat diarrhoea in calves.
- Some of these remedies also destroy the beneficial bacteria in the intestinal tract, which worsens the diarrhoea, even in healthy calves.
- Potentiated sulphas are a good first line of defense.
- Other good options are the more modern antibiotics, such as cephquinone or fluorphenicol.
- The second important step in the treatment of a paratyphoid case (or any other diarrhoea problem)is to treat the dehydration and electrolyte balance.
- This supporting treatment is just as important as administering the correct antibiotic.
- Factors to consider before starting this expensive treatment:
- Animals that are treated and recover usually do not reach their full potential and remain under-performers.
- Animals that recover are often carriers and transmitters of salmonella without themselves showing any signs of the disease.
- Just as in the case of a calf permanently infected with viral diarrhoea, a salmonella carrier is the most important source of continued infection of cattle in the herd on the farm.
- In this case, prevention is better than cure.
- Inoculation and a carefully thought out management system are the only ways that the negative impact of salmonellosis can be overcome.
- Inoculation with a good quality vaccine will also reduce the cost of treating paratyphoid with antibiotics.
- Calves may be inoculated with a live vaccine when they are 1 to 3 weeks old.
- A great advantage of this is that the live vaccine is relatively inexpensive, but this is about the only advantage.
- The live vaccine contains only the S. Dublin strain, and if S. Typhimurium causes the problem on the farm, the calves will have no protection against paratyphoid.
- In addition, S. Typhimurium affects calves younger than 4 weeks of age.
- Another disadvantage of the live vaccine is that the young calf’s vulnerable immune system is relied on to react to the vaccine and one cannot be certain that this will happen.
- The other option is to use a vaccine that contains both S. Dublin and S. Typhimurium and to inoculate the cow with it just before calving.
- It has been shown that antibodies the calf ingests in the colostrum is, generally, considerably more effective in protecting the calf against salmonellosis.
- The dam’s antibodies circulate in the calf and so, for a while, it does not itself have to fight the pathogenic bacteria.
- This article was written by Dr. Barry Coats and appeared in the July and August 2007 issue of The Dairy Mail.