Bovine Adenovirus

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Also known as: BAdV

Introduction

Bovine Adenovirus belong to the Adenoviridae family.

Most adenovirus infections in cattle involve either the respiratory (e.g. rhinitis) or gastrointestinal tracts. In addition there have been reports of adenovirus associated with conjunctivitis, keratoconjunctivitis, and weak calf syndrome. It is now also thought to contribute to the disease complex Enzootic pneumonia of calves. Bovine adenoviruses have also been isolated from healthy cattle.

Currently there are 10 recognised serotypes of adenovirus in cattle

Distribution

Bovine adenoviruses are found worldwide and are particularly widespread in Central America and Africa.

Pathogenesis

The respiratory and enteric tracts are the primary targets for adenovirus infection which usually results in cell lysis and virus shedding, but some cells accumulate virus particles in the nucleus establishing persistent infections.

Respiratory and faecal shedding usually last for about 10 days and, where the kidney is involved, virus can be excreted for over 10 weeks in urine. With persistent infection, lysis of fragile infected cells produces virus-shedding resulting in infection of susceptible animals that come in contact with the virus.

Signalment

Adenoviruses are generally confined to one host species or closely related species.

Bovine Adenovirus can infect cattle and zebu of any breed, sex or age, however, younger animals are more at risk as their maternal antibody begins to wane, around the age of 2 weeks to 4 months old. Experimentally, the virus has also been shown to infect goats and sheep.

Clinical Signs

Signs involving the gastrointestinal tract include diarrhoea with mucus, melena or haemoatochezia, anorexia or reduced appetite, abdominal distension and possible dysphagia.

Respiratory signs include coughing +/- blood, serous nasal discharge, dyspnoea and tachypnoea. This may progress to bronchopneumonia if secondary bacterial infection is present.

Generalised clinical signs include pyrexia, weight loss, sudden death, lymphadenopathy and generalised weakness. The animal will also be dull, depressed and lethargic.

Diagnosis

Clinical signs and physical examination may add Bovine Adenovirus to the differential list, but definitive diagnosis cannot be achieved.

Because adenoviruses can be isolated from apparently healthy cattle, isolation of adenoviruses from clinically sick calves does not necessarily mean that the isolated adenovirus type plays an aetiological role in the clinical disease. For adenovirus to be considered as the aetiologic agent in a particular disease, the antibody titre should be low at the onset of the infection and result in at least a four-fold increase in neutralizing antibodies.

Adenovirus infection can be diagnosed morphometrically, serologically, and by virus isolation. Rapid presumptive diagnosis can be made either by observation of characteristic virus morphology in intranuclear inclusions by transmission electron microscopy or by immunofluorescent or immunohistochemical labelling of adenovirus antigens in tissues with gross lesions.

Because of the number of types of adenoviruses infecting cattle, virus isolation is necessary to definitively identify the virus. Virus can be isolated from nasal secretions, tracheal fluids, intestinal contents and tissue homogenates.

On post mortem examination characteristic features may lead to the diagnosis of BAdV, such as atelectasis and consolidation of the lungs and erosions, ulcerations and haemorrhage in the intestinal tract. Bronchiolar, mediastinal, and mesenteric lymph nodes are usually enlarged. Microscopically the basic lesion is bronchiolitis with necrosis and sloughing early and hyperplasia later in the course of the infection.

Amphophilic, intranuclear inclusions are seen in swollen cells in the respiratory epithelium and sloughed in the lumen. Where the gastrointestinal tract is involved, the basic lesions are fibrinonecrotic plaques overlying foci of haemorrhage and necrosis. Amphophilic intranuclear inclusions are seen in enterocytes as well as in vascular endothelial cells.

Treatment

When economically feasible, cattle can be treated to provide relief from clinical signs associated with adenoviral infection.

Because secondary bacterial infections such as Mannheimia haemolytica, Pasteurella multocida and Haemophilus somnus are common in cattle, antibiotics are often used as part of the treatment.

Control

The main control measure is to ensure adequate colostrum at birth as passive transfer provides immunity to calves.

Other control strategies include preventing mixing of calves of different age groups and ensuring good hygiene and ventilation in calf housing.

Both modified live and inactivated adenovirus vaccines have been developed and evaluated for use in cattle and they should be administered when maternal antibodies have waned, but 2 to 3 weeks before calves from different places are assembled under stressful conditions. Such vaccines are available in Europe (not UK) and Japan, but not in the USA. Most vaccines are formulated in combination with other agents. Two to four doses of vaccine administered subcutaneously or intramuscularly are recommended to provide proper protection. Vaccination has not eliminated infection entirely, but has resulted in the reduction in disease incidence and treatment costs.

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References

Baber, D. J., Candy, J. B (1981) Isolation and characterization of bovine adenoviruses types 3, 4 and 8 from free living African buffaloes (Syncerus caffer). Research in Veterinary Science, 31(1):69-75.

Belák, S., Palfi, V (1974) An adenovirus isolated from sheep and its relationship to type 2 bovine adenovirus. Archiv für die gesamte Virusforschung, 46(3-4):366-369.

Benkö, M., Bartha, A., Möstl, K., Bürki, F (1989) A heteroploid permanent cell line originating from embryonic calf thyroid supporting the replication of all known bovine adenovirus serotypes. Veterinary Microbiology, 19(4):317-324; 10

Boros, G., Graf, Z., Benkö, M., Bartha, A (1985) Isolation of a bovine adenovirus from fallow deer (Dama dama). Acta Veterinaria Hungracia, 33(1-2):119-123.

Davies, D. H., Humphreys, S (1977) Characterization of two strains of adenovirus isolated from New Zealand Sheep. Veterinary Microbiology, 2:97-107.

This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project. The datasheet was accessed on 03 April 2011.

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