Yersinia pestis (nonmotile, non spore forming anaerobic gram-negative bacterial rod)

Humans and domestic animals are alternate hosts for Yersinia pestis, which is maintained by chronic bacteremia in wild rodents and transmitted by fleas. Dog and cat fleas are poor vectors for Y. pestis. In the United States, prairie dogs, rock squirrels and ground squirrels are commonly infected hosts. Y. pestis is associated with semiarid cooler climates adjacent to the desert such as in New Mexico, Arizona, California, Nevada and Colorado.

Transmission occurs by flea bites or contact with mucosa or broken skin with the organism. Domestic and wild cats are susceptible to Y. pestis and can be the source of infection to people. Dogs, raptors, coyotes, raccoons, skunks are resistant to infection but may transport infected fleas.

Cats and dogs are infected by ingestion of infected rodents or bites from the rodent’s fleas. 75% of cats infected with Y. pestis have been associated with rodent hunting behavior. Humans can contract Y. pestis directly through contact with blood, pus or aerosols from infected animals. The number of cases of Yersinia pestis in humans is rising as humans and their domestic pets encroach on wild populations. As human growth expands into once undeveloped areas the chance of transmission between wild rodents and cats/dogs dramatically increases.

Cats are the largest concern for zoonotic spread of Y. pestis to veterinarians.

Cats

The three forms of the disease are bubonic plague, septicemic plague, and pneumonic plague. Bubonic plague is associated with high fever, anorexia, lethargy and lymphadenopathy. Lymph nodes may abscess and drain with hematogenous and lymphatic spread possible. Bubonic plague is the most common and least fatal. Septicemic plague occurs when Y. pestis spreads hematogenously to almost every organ of the body. Clinical signs include, fever, shock, DIC, leukocytosis and death can be possible within 1-2 days after bacteremia begins. Pneumonic plague is an infection of the lungs that occurs following inhalation of the organism or systemic spread. it is the most fatal, yet least common, form of plague. Clinical signs include ocular discharge, vomiting, diarrhea, weight loss, cellulitis, and tonsillitis.

Diagnosis:

Plague should be considered in any febrile cat in an endemic area with gram-negative organisms on fine needle aspirates. Diagnosis can be made with bacterial culture and fluorescent antibody staining.

Treatment: Open and drain the swollen lymph nodes and antibiotics (gentamicin or other aminoglycosides) for a minimum of 21 days and beyond resolution of clinical signs. If plague is suspected the animals should be started on antibiotics before laboratory confirmation. All plague suspects should be handled by people wearing gloves, gowns, and surgical masks. Animals with respiratory signs should have thoracic radiographs taken to evaluate for pneumonic plague. Animals or people exposed to plague can be treated prophylactically with tetracycline for 7 days.

Humans

Incubation is 2-6 days. Bubonic plague is the most common causing fever and swollen tender lymph nodes. Pneumonic plague with systemic involvement of the lungs occurs via inhalation of the organism and has a mortality rate of > 50% in humans if not promptly treated. The major reason for death is patient delay in seeking treatment and lack of recognition of the disease by doctors. People can become infected through inhalation of respiratory droplets, handling infected tissues or bodily fluid, contact with broken skin or mucosa and bites of plague-infected fleas. Local and state health authorities should be notified early in the management of plague infected animals.

Diagnosis: bacterial culture and serology

Treatment: Contact physician immediately with suspected animal plague case.

Prevention: People and domestic animals have intruded on wild populations where plague naturally exists. Elimination of plague in wild populations is impossible. Flea control is very important for dogs and cats in endemic areas. Dogs and cats should not be allowed to come in contact with wild rodent populations. Masks, gowns, and gloves should be worn when handling cats with abscesses especially in the western and southwestern United States.

EMERGING ZOONOTIC DISEASE MENU | SCENARIO #8