Cardioviruses

Cardioviruses are picornaviruses producing enteric infection in a wide range of mammals. Similar to polioviruses, certain strains may, under specific conditions, invade the central nervous system and produce neurodegenerative disease. Theiler's mouse encephalomyelitis virus (TMEV) — occasionally in a more popular manner referred to as mouse polio — can be divided into three groups of substrains infecting mice, i.e., GDVII, FA, and DA. Some not well described strains infect rats.135,136 Antibodies to TMEV are a common finding in rats,99 however, without any clinical signs. GDVII and FA are far more virulent than DA, but in most cases, spontaneous infections are asymptomatic. GDVII may cause acute encephalitis. Paralysis develops when the virus leaves the gray matter and infects the white matter, thereby damaging the upper motor neuron system.137 CD-1, DBA/2, SJL, and SWR mice seem to be far more susceptible.138 DA causes a more long-term demyelinating disease. In infected colonies, prevalences are generally high, and the virus may be transmitted intrautero,139 which may complicate rederivation.

Encephalomyocarditis virus (EMCV) is a virus commonly used for experimental infection of mice, especially in diabetes research.140 However, spontaneous infections have not been found in mice.

Guinea pigs may also harbor a cardiovirus, the causative agent of the disease guinea pig lameness, which is a paralytic and mortal disease. Deficiency of vitamin C may be a predisposing factor, allowing spread to the central nervous system; therefore, in colonies, outbreaks are likely to occur if for accidental reasons the content of vitamin C in the diet is low.141 Serological studies have revealed the presence of antibodies against TMEV in guinea pigs suffering from lameness,142 but DNA technique shows that the virus is probably closely related to EMCV.114 This virus is rather common in laboratory guinea pigs,142 but it is seldom monitored by commercial breeders.

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