Bovine ephemeral fever (BEF), commonly known as three day sickness, is a disease of cattle and occasionally buffaloes. It is marked by short fever, shivering, lameness and muscular stiffness. Caused by a virus, the disease is widespread in Queensland.
The disease causes serious economic losses through deaths, loss of condition, decreased milk production, lowered fertility in bulls, occasional abortions, delays in marketing and restrictions on the export of live cattle.
Ephemeral fever in Australia
First reports of the disease in Australia were received in March 1936 from three widely separated areas: the Kimberley area of Western Australia, the Barkly Tableland in the Northern Territory and Burketown in Queensland.
From areas close to the Gulf of Carpentaria, it spread rapidly eastwards, reaching the coast near Townsville the following September. By December, ephemeral fever had spread to the subcoastal areas adjacent to the Queensland-New South Wales border. The rapid spread to the south continued until, in March 1937, outbreaks were reported in the eastern districts of Victoria.
Now the disease occurs in most years in northern Australia, though it is less common in drought years. The disease usually spreads in a north-south direction, is and governed by season and rainfall.
Spread of ephemeral fever
It is generally believed that the virus that causes ephemeral fever is transmitted between cattle by flying insects. The transmitting insects (vectors) have not been definitely identified, though it is thought that mosquitoes and biting midges (sandflies) are responsible. The spread of the disease depends on the season and weather conditions - rain and prevailing easterly and southerly winds are necessary for the survival and dispersal of vectors. The National Arbovirus Monitoring Program (NAMP) monitors the spread of ephemeral fever virus within Australia.
In most years, BEF cases start at the beginning of the wet season in northern Australia, and then spread south and east down the east coast. It then spreads into southern Queensland, and central and coastal New South Wales. Occasionally, as in 2010, outbreaks occur in southern NSW and northern Victoria.
Animals at risk
Most of the cattle in Queensland graze in areas where ephemeral fever has occurred since 1975. Once exposed to the virus, cattle develop a long-lasting immunity. Calves are relatively immune to ephemeral fever from maternal protection until they are about six months old. Older cattle generally have immunity from previous exposure, with introduced or young growing cattle being most susceptible to disease.
However, outbreaks of disease affecting cattle of all ages can occur at the end of a series of drought years because lack of rain will have prevented the breeding of insect vectors during the drought. Cattle born during the drought will not have been exposed to the virus as younger animals and older immune animals will have been sold off.
Additionally, as you go further south, the necessary favourable conditions for widespread insect vector breeding (moisture and warmth) occur less often, which does not favour disease transmission. Consequently, in southern areas, it is more common to see outbreaks every few years with severe disease and older animals being affected.
Typically, three stages of the disease are recognised. The acute febrile stage appears suddenly, and is especially noticeable in dairy cattle. Cattle show signs associated with a fever. Their rectal temperature will generally be over 40oC. Approximately 50 per cent of sick animals shiver. Sick cattle stand with their backs arched and heads held low with muzzles extended, drooling saliva. Often there is a discharge from the eyes and nostrils. Feeding and cud chewing stop, and milk production is reduced, especially in dairy cows.
The second stage is muscular stiffness and lameness in one or more limbs. Some secondary bloat may also occur due to genera inflammation of the abdominal cavity and ruminal stasis. The lameness may shift between limbs. Joints may be visibly swollen.
During the recovery stage, most affected animals resume eating and drinking. Animals may go down, with heavy animals in good condition being most affected. Some animals remain down due to muscle damage or damage to the spinal cord from constant struggling. Generally, about 1 per cent die or are destroyed because they cannot get up, though this figure may be as high as 10 per cent. Some animals that recover from ephemeral fever have the staggers due to spinal cord damage. Abortions can occur in cows due to the fever.
Often, nothing of significance is observed at post-mortem examination. Occasionally there is excess pinkish coloured fluid in the joints, bloodstained fluid in the heart sac, the chest and abdominal cavities. Post-mortem examination is important to rule out other acute febrile diseases that often occur under the same conditions as ephemeral fever, such as tick fever.
The diagnosis of ephemeral fever during epidemics is made on the presence of lameness, muscular stiffness, pain, rapid spread of the disease through herds and short fever. The ephemeral fever virus can often be cultured from a blood sample taken from animals in the early fever stage of the disease. A PCR test can also identify the presence of the virus, and is most successful when samples are collected in the first few days of clinical disease. Alternatively, two blood samples, the first obtained during the fever stage and the second 14 days later, can be examined for development of antibodies to ephemeral fever virus.
Treatment with anti-inflammatory drugs has been shown to reduce the course of the disease. Consult your veterinarian for an appropriate anti-inflammatory drug, considering the withholding period of the drug for meat and milk.
Most animals will recover if provided with water, shade and food.
A vaccine is registered for the prevention of bovine ephemeral fever. Only cattle older than six months should be vaccinated. The vaccine is available only from veterinarians.
It is a modified live vaccine and has been available since the late 1980s. It is a two-part vaccine - a freeze-dried vaccine and chilled liquid adjuvant that must be mixed prior to administration.
This vaccine has provided good levels of protection against BEF. Field observations have shown that some vaccinated cattle can develop mild disease even after vaccination. However, the severity and duration of illness is very much less than in unvaccinated cattle. You must take great care with this vaccine to get the full benefit. Keep both the freeze dried pellet and the diluent chilled between 2-8oC and then mix it up immediately prior to administration. Note, the freeze-dried pellet should not be frozen as with the previously registered product.
Two injections of the vaccine, 2-4 weeks apart, under the skin of the neck are necessary for long-lasting protection. To ensure that animals are fully immune before insect populations have the opportunity to breed, it is recommended that you complete vaccination before the spring, especially in northern Australia.