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Salmonella

Salmonellosis is caused by many species of salmonellae and characterized clinically by one or more of 3 major syndromes—septicemia, acute enteritis, and chronic enteritis. The disease is seen worldwide and in all animals. The incidence has increased with the intensification of livestock production.

Young calvesusually develop the septicemic form. Adult cattle commonly develop acute enteritis and chronic enteritis may develop occasionally in cattle.

In calves, the disease is usually endemic on a particular farm, with sporadic explosive outbreaks. Subclinical infection with occasional herd outbreaks may be seen in adult cattle. Stressors that precipitate clinical disease include deprivation of feed and water, minimal levels of nutrition, long transport times, calving, and mixing and crowding in feedlots.

Diagnosis:

This depends on the clinical signs and on the laboratory examination of feces, tissues from affected animals, feed (including all mineral supplements used), water supplies, and feces from wild rodents and birds that may inhabit the premises. The clinical syndromes usually are characteristic but must be differentiated from several similar diseases.

Treatment:

Early treatment is essential for septicemic salmonellosis, but there is controversy regarding the use of antimicrobial agents for intestinal salmonellosis.

However, the intestinal form is difficult to treat effectively in all species. Although clinical cure may be achieved, bacteriologic cure is difficult, particularly in adult animals, because the organisms become established and are intermittently shed, which causes chronic relapsing enteritis and contamination of the environment.

The usual route of infection is oral and, after infection, the organism multiplies in the intestine and causes enteritis.

Clinical Findings

Septicemia is the usual syndrome in newborn calves. Illness is acute, depression is marked, fever (105-107°F) is usual, and death occurs in 24-48 hr. Nervous signs may be seen in calves; these animals may also suffer from pneumonia. Mortality may reach 100%.

Acute enteritis is the common form in adults as well as in calves that are usually ≥1 wk old. Initially, there is fever (105-107°F), followed by severe watery diarrhea. In a herd outbreak, several hours may lapse before the onset of diarrhea, at which time the fever may disappear. The feces, which vary considerably, may have a putrid odor and contain mucus, shreds of mucous membrane, and in some cases, large blood clots. Rectal examination causes severe discomfort and straining. Milk production often declines precipitously in dairy cows.
There may be a high incidence of abortion in cows. In cattle, the first signs may be fever and abortion, followed several days later by diarrhea.

Chronic enteritis is a common form in adult cattle. There is persistent diarrhea, severe emaciation, intermittent fever, and poor response to treatment. The feces are scant and may be normal or contain mucus or blood.

Treatment

Broad-spectrum antibiotics are used parenterally to treat the septicemia. Treatment should be continued daily for up to 6 days. Oral medication should be given in drinking water because affected animals are thirsty due to dehydration, and their appetite is generally poor. Fluid therapy to correct acid-base imbalance and dehydration is necessary. Calves and adult cattle need large quantities of fluids. Dying bacteria can release endotoxin. Anti-inflamatories may be used to reduce the effects of endotoxemia.

Control and Prevention

These are major problems because of carrier animals and contaminated feedstuffs. The principles of control include prevention of introduction and limitation of spread within a herd.

Prevention of Introduction: Every effort must be made to prevent introduction of a carrier; animals should be purchased directly only from farms known to be free of the disease and should be isolated for ≥1 wk while their health status is monitored. Ensuring that feed supplies are free of salmonellae depends on the integrity of the source.

Limitation of Spread Within a Herd: In an outbreak, the following procedures should be implemented:

The prophylactic use of antibiotics may be considered.
Movement of animals around the farm should be restricted to limit infection to the smallest group.
Random mixing of animals should be avoided.
Feed and water supplies must be protected from fecal contamination.
Contaminated buildings must be vigorously cleaned and disinfected.
Contaminated material must be disposed of carefully.
All persons should be aware of the hazards of working with infected animals and the importance of personal hygiene.
Ue of a vaccine should be considered, particularly in an outbreak involving pregnant cattle in which a vaccine has been shown to confer some protection in adults and calves.

Salmonella Vaccines: The commercial vaccines available for use in cattle appear to induce a modest level of protection. When given to pregnant cows, they induce antibodies in colostrum, which provide an important measure of protection to calves, which are most susceptible in the first week of life.