Yersinia Pestis Infection in Cats

Abstract

Overview: Plague, the medieval ‘Black Death’, is caused by a Gram-negative coccobacillus, Yersinia pestis, which also infects cats. As in people, it is transmitted from rodents through flea bites; it occurs in Asia, Africa and the Americas in flea-infested regions, all year round, and where rodent reservoirs are abundant. A poor prognosis is associated with high fever, and the pulmonary and septicaemic forms. Antibiotic therapy, flea control and avoidance of rodent contacts have made this infection manageable.

Agent properties

Yersinia pestis, a Gram-negative coccobacillus that belongs to the family Enterobacteriaceae, is the causative agent of plague, a rare but often fatal zoonosis of historical significance in Europe (Black Death). Y pestis is resistant to low temperatures and freezing, and sensitive to high temperatures. ¹

Epidemiology and vectors

Plague occurs in Asia, Africa and the Americas in semi-arid areas, where fleas are active all year round and rodent reservoirs are abundant. Epizootics in rodents expose humans and domestic animals to plague. ¹ Transmission occurs via flea bite or ingestion of infected rodents or lagomorphs. ² Less common is transmission through mucous membranes, skin lesions or inhalation of infected aerosols from individuals suffering from the pulmonary form. Xenopsylla cheopis fleas that have fed on bacteraemic rodents are efficient transmitters of the infection – for more than 1 year – to nearly all mammals. However, not all flea species are efficient vectors: Ctenocephalides species are considered poor transmitters of plague. ¹

Clinical signs

The prognosis for a cat with high and continual fever is poor. ³ The bubonic form is most common and usually involves the mouth (necrotic stomatitis) and mandibular or sublingual lymph nodes when the infection is acquired by preying on infected rodents; drainage of abscesses is a favourable prognostic factor (Figure 1). Septicaemic forms may involve any organ (mainly the lungs), with a clinical presentation of endotoxic septic shock and death in 48 h. The pulmonary form has the worst prognosis and may derive from one of the previous forms or, rarely in the cat, occur as the primary form.^2,4 The overall mortality rate is about 50%. ¹

Figure 1

Cat recovering from plague and submandibular bubo. Image courtesy of the Centers for Disease Control and Prevention, www.bt.cdc.gov; http://emergency

Diagnosis

Clinical suspicion is confirmed by cytology on smears from draining lesions, where only Gram-negative organisms with a bipolar safety-pin shape are seen. ¹ Bacteria can be isolated from the tonsils, blood or other infected tissues by reference laboratories; transportation is subject to class II precautions (hazardous agents). A fourfold rise in antibody titre on serology confirms an acute infection [EBM grade III]. ¹

Treatment

Gentamicin is the drug of choice; doxycycline is used in less severe cases (bubonic form) or for prevention [EBM grade III]. ⁵