Rotavirus infections

Rotavirus infections

A D STEELE, A GEYER AND G H GERDES

Introduction

Rotaviruses are ubiquitous in nature and generally cause infection of the small intestine in the young of many mammal and bird species. The disease occurs predominantly in intensively reared animals and is characterized by acute disease, an ultra-short incubation period, anorexia and diarrhoea.

Rotavirus infection was first recognized in 1963 in mice,1 followed by isolation of the SA11 (simian agent 11) in vervet monkey cell culture.9, 50 In 1969 virus particles (70 nm in diameter) were detected in bovine faeces and were shown to be associated with diarrhoea in calves.59 These murine,63 simian and bovine agents were later found to share a common group antigen and to be morphologically indistinguishable by transmission electron microscopy (TEM). They are now classified in the family Reoviridae, genus Rotavirus, 30, 52 and each rotavirus is named after the species in which it occurs.

Bovine rotaviruses (BRV) were among the earliest rotaviruses to be successfully adapted to tissue culture57 and thus significant research has been directed at them. Much is known of their antigenic relationships, gene structure and function, immunity, epidemiology and pathogenesis. Rotaviruses have a world-wide distribution and commonly affect calves,58 lambs,54, 83 piglets,7, 75 and foals.23, 36 In South Africa they have been detected in calves,93 piglets,72 and goat kids.26 Several reviews have been published.33, 38, 53

Aetiology

Rotaviruses have a distinctive morphology, revealed by TEM of negatively stained virus in faeces (figure 108.1). Rotaviruses from different species and different serogroups are morphologically indistinguishable by TEM, and consist of a non-enveloped virion with icosahedral symmetry.38 Three types of particles can be seen. The triple-layered virion is the complete infectious particle, the outer capsid of which has a sharply defined outline resembling the rim of a wheel. The name rotavirus derives from the Latin ‘rota’ meaning wheel.38 approximately 70 nm in diameter.15 The double-layered particle or inner capsid particle has a rough bristly appearance and is approximately 55 nm in diameter. The electron-dense core is hexagonal and approximately 37 nm in diameter.37

The core contains 11 segments of double-stranded RNA (dsRNA). The segments can be readily separated by polyacrylamide gel electrophoresis (PAGE) and range in size from 0,2 × 106 to 2,2 × 106 Daltons, with a total molecular weight of 11 to 12 × 106 Daltons.32 When separated by PAGE the 11 segments of dsRNA produce a characteristic pattern known as an RNA electropherotype.76

The dsRNA segments can be divided into four class sizes (I to IV) based on migration through PAGE (figure 108.2). The group A rotaviruses have a characteristic 4-2-3-2 PAGE pattern which is generally conserved among these viruses. However, group B and C rotaviruses, which are also found in most domesticated livestock, have distinct patterns which allow rapid differentiation of strains from different serogroups.2, 69, 85

The group B strains have a characteristic RNA electropherotype where the segments cluster in a 4-2-2-3 pattern, and the group C rotaviruses exhibit an electrophoretic pattern of 4-3-2-2.69, 85 The strains from the different serogroups of A, B and C rotaviruses also have distinct group antigens (see below).

Group A rotaviruses have been isolated from calves, piglets, lambs and foals, and are the most studied. Nevertheless, rotaviruses from the different serogroups (specifically groups B and C) have been recovered from the faeces of all of these species.21, 85

In most animal rotaviruses the classical RNA electropherotype is long, where the 11th gene segment is smaller in size and generally migrates further in PAGE. Virtually all BRV group A strains exhibit a long RNA electropherotype with some variation in the migration of individual segments (figure 108.2), although limited numbers of BRVs with a short RNA electropherotype have been reported.92 This is also true for the porcine rotaviruses (PRV) where most strains exhibit a long RNA electropherotype, although isolated short strains have been identified.3 To date, all equine and ovine rotaviruses have exhibited a long RNA electropherotype.

Figure 108.1 Rotavirus particles viewed by electron microscopy in a faecal filtrate from a calf with diarrhoea.

Figure 108.2 Polyacrylamide gel electrophoresis of the 11 segments of dsRNA from a bovine rotavirus. The RNA segments are numbered from largest to smallest and show the classic group A rotavirus configuration of 4-2-3-2 segments separated in a 10 per cent polyacrylamide gel run at 4 °C overnight

Figure 108.3 PAGE gel showing the differences in segment migration configuration of group A, B and C rotaviruses recovered from piglets with scours

In South Africa group-A BRVs with a long RNA electropherotype have been identified in both dairy and beef herds,25 and PRV strains with a long electropherotype have been reported in different herds of pigs.40 Group A rotaviruses with a long pattern were detected in a single goat herd.27 Furthermore, rotaviruses with the classical group B and group C RNA electropherotypes have also been detected amongst PRVs isolated in South Africa41 (figure108.3).

Considerable antigenic diversity is found among the rotaviruses, and isolates are classified...

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