Paramyxoviruses

Parainfluenzaviruses are unstable viruses producing nonpersisting infection in immunecompetent rodents and persisting infection in immune-deficient rodents.143,144 They may be divided into type 1, type 2, type 3, and type 4, the latter, however, have only been found in humans. Sendai virus, a type 1 parainfluen-zavirus, produces respiratory infections in rats and mice. Isolates are antigenically alike and show the same pathogenecity for both species. Clinical symptoms are rare, but a high mortality may be seen in young mice before or around weaning. DBA/2 and 129 mice may be more sensitive than other strains.145 Pathological signs are catarrhal bronchitis eventually extending into the alveoli of the lung. Transmission is mainly respiratory.146 Diagnosis can easily be made by serology, but the virus does not spread efficiently among sentinels by the dirty bedding technique.147 Rabbits may be experimentally infected by Sendai virus,148 and spontaneously occurring antibodies have also been found in rabbits.149 Antibodies to Sendai virus have also been revealed in guinea pigs,69 but as Sendai virus has not been isolated from guinea pigs and experimental infection has not been achieved, these antibodies have probably been cross-reactions from guinea pig parainfluenza virus. This type 3 parainfluenza virus was not isolated from guinea pigs until 1998,150 but antibodies were found in guinea pigs already in the 1970s.151 Guinea pig parainfluenza virus type 3 is a lineage of human parainfluenza virus type 3, probably introduced into guinea pig colonies via infected humans.150 Serological screening for antibodies, e.g., enzyme-linked immunosorbent assay (ELISA), is at present the diagnostic method of choice, but as the guinea pig parainfluenza virus is not commonly available as antigen bovine parainfluenzavirus type 3 must be used for testing guinea pigs. In infected breeding colonies, all parainfluenzaviruses normally have high prevalences.

Infection with the pneumovirus, pneumonia virus of mice (PVM), causes a normally silent infection in mice, rats, hamsters, and gerbils. Serological prevalences are high in infected colonies, but pathological symptoms are absent in immune-competent mice. Weak pathological changes may be found in rats and in nude mice. In the latter, infection is also persistent,143 in contrast to all immune-competent animals, which clear themselves of the infection. Current screening can be made by serology.

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