Bovine Ephemeral Fever

Ephemeral fever is a non-contagious disease of cattle caused by bovine ephemeral fever virus (family RHABDOVIRIDAE, genus EPHEMEROVIRUSE).

The virus has been isolated from various species of midges and mosquitoes which are probably the main vectors. Present in Africa, the Middle East, Asia, and Oceania. Clinically-affected cattle are generally 6-months to 2-years of age but all ages are susceptible. Signs are usually mild and last for just a few days but high morbidity can cause loss of milk in dairy herds making this an important viral diseases of cattle.

Additional information

Ephemeral fever is an insect-transmitted, noncontagious, viral disease of cattle and water buffalo that is seen in Africa, the Middle East, Australasia (excluding Papua New Guinea and New Zealand), and Asia south of the former USSR. In apparent infections can develop in cape buffalo, hartebeest, waterbuck, wildebeest, deer, and possibly goats.

Signs, which occur suddenly and vary in severity, include biphasic to polyphasic fever, shivering, inappetence, lacrimation, serous nasal discharge, drooling, dyspnea, atony of forestomachs, depression, stiffness and lameness, and a sudden decrease in milk yield. Affected cattle may become recumbent and paralyzed for 8 hr to >1 wk. After recovery, milk production often fails to return to normal levels until the next lactation. Abortion, with total loss of the season’s lactation, occurs in ~5% of cows pregnant for 8-9 mo. The virus does not appear to cross the placenta or affect the fertility of the cow. Bulls, heavy cattle, and high-lactating dairy cows are the most severely affected, but spontaneous recovery usually occurs within a few days. More insidious losses may result from decreased muscle mass and lowered fertility in bulls.

Diagnosis

Single cases are difficult to diagnose, but with a herd outbreak, when cattle at various stages of disease can be examined, diagnosis is made from clinical observations and the history of the outbreak.

Diagnosis is based almost entirely on clinical signs in an epidemic. All clinical cases have a neutrophilia with the presence of many immature forms, although this is not pathognomonic.

Laboratory confirmation is by serology, rarely by virus isolation. Whole blood should be collected from sick and apparently healthy cattle in affected herds. Samples must be sufficient to provide 2 air-dried blood smears, 5 mL in anticoagulant (not EDTA), and 20 mL for serum.

Isolated viruses are identified by neutralization tests using specific ephemeral fever virus antisera and by ELISA using specific monoclonal antibodies. The neutralization test and the blocking ELISA are recommended for antibody detection and give similar results. A 4-fold rise in antibody titer between paired sera collected 2-3 wk apart confirms infection.