A trial of molecular epidemiology using bovine enteroviruses isolated monthly from cattle

Antigenic analysis of type O foot-and-mouth disease virus in the persistently infected bovine

The antigenic profiles of serotype O strains of FMDV collected from the oropharynx of persistently infected cattle were defined with a panel of monoclonal antibodies (mAb's) in an indirect antigen-trapping ELISA. The mAb profiling showed no significant loss of reactivity in two neutralising antigenic sites of persistent FMDV isolates collected over a period of eight months. Early and late serum taken from a carrier animal showed similar neutralising activity against early and late carrier isolates. The antigenic stability of serotype O strains of FMDV collected during the carrier state suggests that antigenic variation facilitated by pressure from the host humoral immune response is not critical to the establishment or maintenance of a persistent infection with FMDV.

Toroviruses of animals and humans: a review

Toroviruses are a group of enveloped positive-stranded RNA viruses that cause enteric, respiratory, and perhaps generalized infections in animals and humans. Their name refers to their unique morphological features: an elongated bacilliform core with two rounded ends is surrounded by a membrane that may either tightly adhere to or “shrink-wrap” it, without respecting the capsid's rod shape; in the first instance, straight or curved rhabdovirus-like particles are formed, whereas in the latter a biconcave disk results. Torovirus history is brief: the first representative, Berne virus (BEV), was isolated in Berne, Switzerland, in 1972 from a rectal swab taken from a horse with diarrhea 1 week before it died. BEV is the only equine torovirus isolate that replicates in cell culture; since most molecular data have been obtained with this isolate, BEV has been acknowledged as the torovirus prototype. Recognition of toroviruses as a new group of potentially pathogenic viruses came seven years after the discovery of BEV, when morphologically similar particles were discovered by electron microscopy (EM) in stool specimens from calves with severe diarrhea in a dairy herd in Breda, Iowa. Despite repeated attempts, BRV has not been adapted to the growth in cell or tissue culture, a problem which has hampered its biochemical, bio-physical, and molecular characterization. However, its pathogenesis and pathology have been studied in the experimentally infected gnotobiotic calves, showing that BRV infections may cause gastroenteritis. Recently, Vanopdenbosch et al. reported the isolation of a torovirus-like virus from the respiratory tract of calves with pneumonia, suggesting that both enterotropic and pneumotropic bovine toroviruses exist. Besides the established toroviruses of horses and cattle, torovirus-like particles (TVLPs) have been found by EM in different animal species; torovirus antibodies appear to be widespread in higher vertebrates, indicating that these viruses infect a broad range of animal hosts. The possibility of a torovirus infecting humans was first reported in 1984 and has become more likely in view of the recent data. This chapter is intended to update the information about toroviruses, and to describe the similarities and differences with the related coronaviruses.

The carrier state in foot and mouth disease--an immunological review

The carrier state in foot and mouth disease (FMD) is characterized by the asymptomatic low-level excretion of foot and mouth disease virus (FMDV) from the oropharynx of ruminants for periods that are species and virus strain-dependent. Persistent infection with FMDV readily occurs following the failure of virus elimination at the acute stage of infection, a process thought to be mediated through the phagocytosis of antibody/virus immune complexes. Recent evidence supports the view that carrier cattle are important in the epidemiology of FMD in the field. The absence of histopathological change in persistently infected tissues and the reduced cytopathology of carrier virus isolates in tissue culture suggest that less lytic FMDV variants are generated or selected in the carrier animal. Altered virus replication, due to attenuation or interference, rather than antigenic variation may therefore allow evasion of the exaggerated FMDV-specific systemic and local humoral immune responses that occur in the carrier state. Although cell-mediated immune mechanisms for FMDV clearance have not been described, the eventual elimination of many persistent virus infections involves this arm of the immune system. Thus, further investigation of cellular elements of the immune response, more particularly the local interaction of mononuclear cell infiltrates with persistently infected cells, represents an area of research that has the potential to elucidate the carrier state problem.