Information for Veterinarians

Background

Cats are highly susceptible to plague and are a common source of Yersinia pestis infection in humans (owners and veterinarians). Dogs infected with plague are less likely to develop clinical illness than cats.

Most cases of plague in cats present with a sub-mandibular lymphadenitis. Abscessed lymph nodes may be clinically indistinguishable from abscesses due to other causes, like bite wounds. Cats with pneumonic plague can pose a significant plague risk to owners, veterinarians and others who handle or come into close contact with these animals due to possible aerosolization of bacteria. Transmission to humans can also occur directly, by bites, scratches, and direct contact with infectious exudates or indirectly, as the pets may carry infected fleas to their owners.

Diagnostic testing

• Y. pestis may be identified microscopically by examination of Gram, Wright, Giemsa, or Wayson’s stained smears of peripheral blood, sputum, or lymph node specimen. Visualization of bipolar-staining, ovoid, Gram-negative organisms with a “safety pin” appearance permits a rapid presumptive diagnosis of plague.
• Appropriate biologic samples for diagnostic testing include: lymph node aspirate, lymph node, liver, spleen, lung, bone marrow, and whole blood.
• Antibiotic therapy should be started promptly, but pre-treatment samples are ideal for diagnostic testing.
• Tissue samples should be placed in a clean container and chilled (not frozen).
• Contact local or state health officials to determine the best place to send samples for diagnostic testing.

Treatment for dogs and cats

• Streptomycin is the treatment of choice, but is difficult to obtain. Alternatives include:
  • Gentamicin (2-3 mg/kg tid, IM or SQ)
  • Doxycycline (5 mg/kg bid, PO)
  • Tetracycline (22 mg/kg tid, PO)
  • Chloramphenicol (50 mg/kg bid, PO)
• Parenteral antibiotics may be switched to oral therapy upon clinical improvement.

Avoiding occupational risks

• Veterinary staff is at risk of plague if there is contact with infectious exudates, respiratory droplets, oral secretions, tissues or fleas.
• Any material used in examination of plague-suspect cats should be disinfected, autoclaved, or incinerated.
• Masks and gloves should be worn when examining and treating cats suspected of having plague.
• Veterinarians should use appropriate personal protective equipment (PPE) before beginning a necropsy on a plague-suspect animal. PPE should include gloves, an N95 respirator or the equivalent, and protective eye equipment.
• If any veterinary staff is exposed to infectious material, they should watch their health closely for 2 weeks following the exposure and discuss post-exposure prophylaxis or fever watch with a health care provider and public health officials.

Prevention and control

It is important that public health officials be notified promptly when plague is suspected in a cat.

• Public health officials will assist with follow-up investigations and implementation of preventive measures at sites where cats might have been exposed to minimize future risk.
• Follow-up will help identify persons who might have been exposed to the infected animal so that appropriate preventive measures, including prophylactic antibiotic therapy if indicated, can be implemented.
• Owners of plague–positive animals frequently ask veterinarians about their own risk of contracting plague. They should be advised:
  • That their risk of plague depends on the type of contact with the infected animal (casual contact versus inhalation of infectious coughed material).
  • To see their health care provider and watch their health closely for 2 weeks following the last possible contact with the infected animal.
  • That post-exposure antibiotic therapy may be warranted, depending on the type and duration of the contact. Health department personnel should be placed in touch with owners of plague-positive animals to ensure no animal–to–human transmission occurs.

General plague prevention messages can be disseminated by veterinarians to animal owners. These include:

• All ill animals, especially cats, should be seen by a veterinarian.
• If you live in areas where plague occurs, treat pet dogs and cats for flea control regularly and do not allow these animals to roam freely.
• Eliminate sources of food and nesting places for rodents around homes, work places, and recreation areas; remove brush, rock piles, junk, cluttered firewood, and potential food supplies, such as pet and wild animal food. Make your home rodent-proof.
• Pet owners should be encouraged to not pick up or touch dead animals.