Gram -ve Zoonotic Rods

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             Zoonoses are human diseases caused by organisms that are acquired from animals.

Some zoonotic organisms are acquired directly from the animal reservoir, whereas others are transmitted by vectors, such as mosquitoes, fleas, or ticks.

Pathogenesis & Epidemiology The organisms enter the body either by ingestion of contaminated milk products or through the skin by direct contact in an occupational setting such as an abattoir.

They localize in the reticuloendothelial system, namely, the lymph nodes, liver, spleen, and bone marrow.

Imported cheese made from unpasteurized goats' milk produced in either Mexico or the Mediterranean region has been a source of B melitensis infection in the United States.

The disease occurs worldwide but is rare in the United States because pasteurization of milk kills the organism.

If organisms are not isolated, analysis of a serum sample from the patient for a rise in antibody liter to Brucella can be used to make a diagnosis.

Prevention Prevention of brucellosis involves pasteurization of milk, immunization of animals, and slaughtering of infected animals.

It has been isolated from more than 100 different species of wild animals, the most important of which are rabbits, deer, and a variety of rodents.

The bacteria are transmitted among these animals by vectors such as ticks, mites, and lice, especially the Dermacenior ticks that feed on the blood of wild rabbits.

The tick maintains the chain of transmission by passing the bacteria to its offspring by the transovarian route.

Disease Yersinia pestis is the cause of plague, also known as the black death, the scourge of the Middle Ages.

Humans are accidental hosts, and cases of plague in this country occur as a result of being bitten by a flea that is part of the sylvatic cycle.

Because the proventriculus is blocked, the flea gets no nutrition, becomes hungrier, loses its natural host selectivity for rodents, and more readily bites a human.

Disease Pasteurella multocula causes wound infections associated with cat and dog bites.