Bovine Adenovirus

Also known as

BAdV

Description

Bovine adenovirus is a member of the Adenoviridae family that causes disease in cattle worldwide—particularly in Africa and Central America. Adenovirus infections in cattle involve either the respiratory or gastrointestinal tracts, with some reports of adenovirus associated with conjunctivitis, keratoconjunctivitis (eye infections), weak calf syndrome and abortion.

Adenovirus infections are also now thought to contribute to the disease complex called Enzootic pneumonia of calves, depending on the serotype of the virus. Bovine adenoviruses have also been isolated from healthy cattle, so they doesn’t always cause disease. Currently there are 10 recognized serotypes of adenovirus in cattle.

Once infected, cattle shed the virus for approximately 10 days in respiratory secretions or feces (depending on location of the infection). Some cattle become persistently infected; the virus may persist in some body cells, resulting in excretion of the virus for a much longer period, exposing more animals to infection.  If the kidney is involved, the virus can be excreted for 10 weeks or longer in urine.

Bovine Adenovirus can infect cattle and zebu of any breed, sex or age, though younger animals are more at risk as their maternal antibody begins to wane, at about 2 weeks to 4 months of age.

Signs of infection range from subclinical to severe, including pneumonia, enteritis, eye problems, weak calf syndrome, and abortion. Respiratory tract and intestinal tract diseases may be concurrent. Infections caused by this virus are often found associated with other viral and bacterial infections.

Signs involving the gastrointestinal tract include diarrhea containing mucus or blood, or dark sticky feces containing partly digested blood, reduced appetite or lack of appetite, abdominal distension and sometimes difficulty swallowing.

Respiratory signs include coughing—with or without blood—thin, clear nasal discharge, and rapid, difficult breathing. This may progress to bronchopneumonia if secondary bacterial infection occurs.

Generalized signs include fever, weight loss, dullness, weakness, swollen lymph nodes and sometimes sudden death. The animal will also be dull, depressed and lethargic.

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,

Signs

• Diarrhea
• Lack of appetite
• Cough
• Rapid difficult breathing
• Lethargy
• Weakness
• Swollen lymph nodes
• Weight loss

Cause

The importance of adenoviruses in livestock is uncertain and may vary. Several serotypes of bovine adenoviruses have been isolated from calves with pneumonia, enteritis, conjunctivitis, keratoconjunctivitis, and weak calf syndrome.

The classification of bovine adenoviruses is complicated because of the lack of genus-specific antigens. Some bovine adenoviruses (Subgroup I: bovine adenoviruses 1–3, 9, and 10) belong to the genus Mastadenovirus, whereas others (Subgroup II; bovine adenoviruses 4–8) are now classified in the genus Atadenovirus.

Definitive diagnosis is difficult, since adenoviruses can be isolated from apparently healthy cattle, and isolation of adenoviruses from clinically sick calves does not necessarily mean that the isolated adenovirus plays an actual role in the clinical disease.

For adenovirus to be considered as the causative agent in a particular disease, the antibody titer should be low at the beginning of the infection and result in at least a four-fold increase in neutralizing antibodies as the disease progresses.

Prevention

The main control measure is to ensure that newborn calves get adequate colostrum at birth, since this passive transfer provides immunity to calves.

Other control strategies include preventing mixing of calves of different age groups and providing clean bedding and good ventilation in calf housing.

Vaccination of young cattle can reduce the severity and incidence of disease, but the vaccine is not available worldwide. The vaccine is not available worldwide. No licensed or marketed BAV vaccines are available in North America. When a vaccine is used, 2 to 4 doses are required and are usually combined with other agents.

Both modified live and inactivated adenovirus vaccines have been developed and evaluated for use in cattle and should be administered when maternal antibodies have waned, and at least 2 to 3 weeks before calves from different places are brought together in stressful conditions. Such vaccines are available in Europe (but not the UK) and Japan, but not in the USA. Vaccination does not eliminate risk of infection, but can result in the reduction of disease incidence and treatment costs.

Treatment

There is no treatment for the virus itself but cattle can be treated to provide relief from clinical signs. Antibiotics are often given, as well, simply to prevent secondary bacterial infections.