Cowpox Virus Infection

Cowpox virus (CPXV), despite its name, is enzootic among wild rodents in Europe and Eurasia, but is infec­tious for humans, cattle, felids, and other hosts, includ­ing rats. Human exposure is most often contracted through infected cats, but recently, a number of human cases have arisen through contact with pet rats in Europe.

Pathology

Experimental infection of laboratory rats demonstrated that intradermal or contact inoculation with CPXV gen­erally resulted in mild dermal manifestations, character­ized as vesiculopustular dermatitis. Intranasal inoculation resulted in severe dyspnea with peracute mortality. His­topathology revealed focal necrotizing lesions in respira­tory mucosa with large eosinophilic intracytoplasmic inclusion bodies (Guarnieri bodies), bronchointerstitial pneumonia, pulmonary congestion and edema, and lymphoid necrosis. Intradermally inoculated rats also developed necrotizing rhinitis, laryngitis, and bronchoin­terstitial pneumonia. Dermal lesions were typically pro­liferative and necrotizing, involving limbs (Fig. 2.10), nose, lips, tongue, and inguinal skin with intracytoplas- mic inclusions within epithelium (Fig. 2.11).

FIG. 2.10. Digit of a rat with cowpox virus lesion. (Source: Briethaupt et al. 2012. Reproduced with permission from SAGE Publications.)

FIG. 2.11. Skin from a rat infected with cowpox virus. Note the many intracytoplasmic inclusions in the follicular epithelium.

(Source: Briethaupt et al. 2012. Reproduced with permission from SAGE Publications.)

Diagnosis

Definitive diagnosis can be achieved by identification of typical pox viral inclusion bodies within lesions, immu­nohistochemistry, or PCR. Human exposure to infected rats is most often associated with skin lesions on the patient's neck. Severe flu-like illness may also be present. Serology, using ectromelia virus as antigen, may be used for surveillance in laboratory rat populations.