EVOLUTION

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SPECIAL SECTION

Bacterial Disease - Hemorrhagic Septicemia

Introduction

HS is an acute pasteurellosis, caused by Pasteurella multocida and manifest by anacute and highly fatal septicemia principally in cattle and water buffalo; the latter are thought to be more susceptible than cattle.

HS occurs infrequently in swine and even less common in sheep and goats. It has been reported in swine and even less common in donkeys.

Infrequently in deer, yak and probably other feral ruminants. Laboratory rabbits and mice are highly susceptible to experimental infection. <>

Etiology

Epidemic HS is caused by one of two serotypes of P.multocida, B:2 and E:2. Serotype E:2 has been recovered only in Africa. B:2 causes the disease elsewhere and also has been recovered from cases in Egypt and Sudan. P.multociada is an extracellular parasite, and immunity is primarily humoral.

Transmission, Epidemiology, Pathogenesis

Infection occurs by direct contact or indirect contact. The source of infective bacteria is thought to be the nasopharynx of bovine carriers. Natural infection occurs by ingestion or inhalation.

The initial site of proliferation thought to be the tonsillar region. In susceptible animals, a septicemia develops rapidly, and death due to endotoxemia ensues within 8-24 hour after the first signs are seen. Exotoxins have not been demonstrated.

The mortality rate is high when the agent is introduced to virgin or nonendemic regions. Losses vary widely in endemic areas.

Clinical Findings

Most cases are acute or per acute, resulting in death within 8 hours after onset. Because the course is so short, clinical signs may easily be overlooked.

Animals first evince dullness, then reluctance to move, fever, salivation, and serous and nasal discharge. Edematous swelling is frequently seen, beginning in the throat and spreading to the parotid region, neck, and brisket.

Mucous membranes are congested. There is respiratory distress, and usually the animal goes down and within hours.

Occasional cases linger for several days. Recovery is rare. There appears to be no chronic form.

Lesions

The most obvious changes in affected animals are the edema, widely distributed hemorrhages, and general hyperemia.

In most cases, there is an edematous swelling of the head, neck, and brisket region. Incision of the swelling musculature, and the sub serous petechial hemorrhages, which are found through the animal, are particularly characteristic.

Blood-tinged fluid is often found in the pericardial sac and in the thoracic and abdominal cavities.

Petechial hemorrhage particularly prominent in the pharyngeal and cervical lymph nodes.

Gastroenteritis seen only occasionally and, unlike pneumonic pasturellosis, pneumonia usually extensive.

Diagnosis

Of particular significance is a history of earlier outbreaks and a recent failure to vaccinate.

Sporadic cases are more difficult to diagnose clinically. The season of the year, rapid course and high herd incidence, with fever and edematous swellings indicate typical HS.

Characteristic necropsy lesions support the clinical diagnosis.

Differential diagnosis

Although typical outbreaks are not difficult to recognize clinically, particularly in endemic regions, acute salmonellosis, anthrax, pneumonic pasteurellosis and rinderpest should be considered.

Treatment

Various sulfonamides, tetracyclines, penicillin and chloramphenicol are effective if administered early.

Because of the rapid course of the disease and the frequent difficulty of access to animals, antimicrobial therapy often is not practicable. Although multiple antibiotic resistances have been reported for some strains of P.multocida, it has not been described for the HS serotypes.

Prevention

The principle means of prevention is by vaccination.

Three kinds of vaccine are widely used: plain bacterin, alum-type precipitated bacterin, and oil-adjuvant bacterin.

The most effective bacterin is the oil-adjuvant-one dose provides protection for 9-12 month; it should be administered annually.

The alum-precipitated-type bacterin is given at 6 months intervals.

Maternal antibody interferes with vaccine efficacy in calves.

The oil-adjuvant vaccine has not been popular because of difficulty in syringing and occasional adverse tissue reactions.

A live vaccine prepared from a B:3,4 serotype of deer origin is being used with reported success in Southeast Asia.


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