Vet's Perspective

Opinion
Nov 23, 2012
by WLJ

Salmonella highlights…

Concerns are ever growing among producers and consumers regarding the safety of our food supply. Any number of bacteria and viruses can adversely affect the production and sale of food commodities in general.

A highly populated region on the farm is breeding grounds for disease transmission. Salmonella species are known to flourish at times of close contact between animals of various ages, such as during calving and comingling of herds. Bacterial infections also tend to arise during less than ideal weather conditions, either too wet or too dry. Efficient management practices are the best method when attempting to reduce disease susceptibility and transmission.

Clinical signs of disease vary, but often include: severe watery and bloody diarrhea, fever, dehydration, inappetence, and weakness. Some pregnant animals may abort, and affected dams may inadvertently starve their calves due to decreased milk production. Mortality rates vary with age and severity of disease in each animal.

The most common type of bacterium to cause infection is the serotype Salmonella dublin, as it appears to be host-adapted to cattle in particular. Not all serotypes are indicative of infection, and many animals will be noted to harbor bacteria without demonstrating any signs of illness.

Potential ‘vectors’ or agents that spread disease can be anything from the tractor and trailer to the farm dog or employees’ unsanitized hands. Many affected animals will be subclinical and never even show signs of illness, yet can spread bacteria profusely.

Species in the Salmonella family are typically very hardy. Managers can help prevent transmission by always working with clinically ill animals before handling herdmates, especially calves and cattle sick with other metabolic disorders (such as milk fever or ketosis). Animals known to be infected with Salmonella should be housed in a quarantine area, and special clothing and instruments should be dedicated to their care.

Testing herds with suspected Salmonella outbreaks is wise in order to attain proper treatment. The preferred source is a fresh fecal sample from live animals; samples should be collected daily for a minimum of five days, as the bacteria may be shed intermittently. Your veterinarian may want to conduct a necropsy on recently dead animals, and will collect appropriate tissue samples for diagnostic testing. Some laboratories may prefer PCR testing on tissue samples; DNA amplification is a newer method being utilized and allows for better sensitivity in detecting infectious bacteria.

Managers are also reminded to quarantine new animals to a herd; routine quarantine duration is typically 30 days in order to assess the animals for signs of illness. Bacteria have been isolated from several environmental sources, such as:

feeders and watering devices, soil, machinery, and instruments that have come into contact with affected animals. It is wise to test affected animals concurrently for BVDV, as association has been noted in herds between the two ailments.

One must never forget the zoonotic potential for Salmonella infections. The bacteria are easily transmitted between humans and animals via contact with contaminated manure and oral fluids. Procedures to decrease transmission include using dedicated clothing when working with sick animals, avoiding overcrowded pens and pastures, good hand washing practices, disposable gloves, and refraining from eating and drinking around animal housing. Vaccines are available and more often used with dairy than beef cattle. Consult with your veterinarian regarding the need for adding Salmonella vaccines to your regular protocol. Herd employees who develop signs of gastrointestinal illness are advised to see their physician for medical care. — Dr. Genevieve Grammer

[Dr. Genevieve Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to drgigi19@ gmail.com.]

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