A viral disease of cattle and buffalo, transmitted by mosquitoes and midges, and more commonly seen in young, immunologically niaive cattle. It is common in northern Australia, especially in wet seasons, and is occasionally seen in more southern areas when climatic conditions favour widespread distribution of the insect vector. Typically, sickness is for three days, usually manifesting as fever, lameness and recumbency. Infection stimulates long lasting immunity.
Heavier, large framed animals are more affected. Infection of light cattle may be inapparent. Deaths may occur when recumbent animals can't rise or when incapacitated animals incur further injury as a result of accidental slips or falls or are trampled by other cattle.
Cattle incubating the disease may become clinically affected after entering the export process and susecptible cattle may become affected after introduction to endemic areas in Australia or overseas.
Sudden onset of recumbency, stiffness and shifting lameness affecting multiple animals should raise strong suspicions. Early in an outbreak sporadic recumbent cases will be detected during pen inspection. Later, multiple animals become recumbent, have difficulty rising, or may be affected by shifting lameness. Physical examination may detect fever (41oC) and muscle stiffness, and often little else. Sometimes there is bilateral discharge from eyes and nose and drooling of saliva and drooped ears.
Specimens for laboratory confirmation of infection include serum collected from animals in the acute and convalescent stages of infection (2-3 weeks apart).
Differential diagnoses include vaccination reactions such as for tick fever; injuries, bruising or exhaustion from transport; overexertion and dehydration from excessive yard handling, especially in hot conditions; and blackleg.
Affected animals need rest - avoid mustering, transporting, loading or discharging sick animals. Recumbent animals are often hypocalcaemic, and will benefit from administration of calcium borogluconate as well as non steroidal anti-inflammatory drugs. Encourage heavy animals to stand to prevent compression damage to muscle and nerves.Mildly affected animals recover in several days without intervention.
Vaccines are available. Cattle from southern Australia should not enter northern Australia without vaccination.