Bovine ephemeral fever: Three Day Sickness
Series: Agfact A0.9.50 Edition: Second edition Last updated: 18 May 2001
Bovine Ephemeral Fever (BEF) is a viral disease of cattle and buffalo. Typically, affected animals are only sick for a few days, hence the alternative name - Three Day Sickness.
There is a sudden onset of fever- as high as 41oC compared with the normal temperature of about 38oC. The temperature returns to normal within 36 hours. The first sign in milking cows is a sudden and severe drop in milk production. Cows in advanced pregnancy may abort. This is probably because of the fever, rather than a specific effect of the virus.
Animals stop eating and drinking and become depressed. They usually drool saliva, develop a stringy nasal discharge, and may have watery eyes.
Affected animals may shiver and often become very stiff with a shifting lameness, and are reluctant to move. Lameness may not become apparent until the second day of illness. The joints may appear swollen and sometimes there is swelling around the jaw. Some animals - particularly the heavier ones - just lie down and refuse to move.
By day three the affected animal is usually standing again and will begin to eat. However, lameness and weakness may last for another two or three days.
In the vast majority of cases the disease runs a short course, followed by rapid and complete recovery. However, the disease can vary in severity. Some animals may show only slight symptoms for about 24 hours, while a small number may stay down for many weeks. The disease is usually milder in calves under 12 months of age.
Milk production usually drops by at least 50% in sick cows. In dairy herds it is the highest producing animals that are usually the most severely affected. Yield should return nearly to normal after about three weeks, but cows affected late in lactation often dry off. Mastitis sometimes develops, with a marked rise in the somatic cell count.
Bulls and fat cows tend to show more severe signs than other cattle. Such animals lose condition rapidly and are slow to regain their body weight. A proportion of bulls will suffer temporary infertility lasting from three to six months because of the high fever. Permanent infertility is uncommon but can occur.
A small proportion of animals that go down may suffer a permanent paralysis due to damage to the spinal cord- either as a direct effect of the virus, or due to injuries if they fall awkwardly.
Although most of the herd can be affected, deaths from ephemeral fever are uncommon and rarely involve more than 1% of the herd. Death is usually the result of misadventure or being down for a long period.
How is BEF spread?
A virus known as a rhabdovirus causes BEF. It is also referred to as an arbovirus because biting insects spread it. The most likely insects to transmit the disease in NSW are mosquitoes, such as Culex annulirostris. Biting midges may also play a role in disease spread, and there may be other vectors that have not been identified.
The distribution of these insects varies with climatic conditions, and this in turn will influence the pattern of disease spread and time of occurrence.
Where does the disease occur?
Before 1975, BEF occurred infrequently in explosive epidemics that swept from north to south throughout eastern Australia - from Queensland, sometimes to Victoria. Large numbers of cattle were affected. These outbreaks occurred at intervals of 10 to 15 years. In the years between these epidemics, the disease was virtually unknown.
BEF has become established now in parts of eastern Australia, with localised outbreaks occurring on the north coast of NSW, or in the Hunter Valley. Depending on the seasonal conditions, the disease has then spread from these centres. Sometimes there is a north-south moving wave of infection from Queensland through NSW but this is now uncommon. The usual pattern consists of sporadic cases for one or two years followed by an outbreak.
Cases in inland NSW are much less common but occasional outbreaks can occur in the north west of the State - usually associated with spread from Queensland. The disease is rare in southern NSW and Victoria but occasional cases have been observed.
When does it occur?
BEF usually occurs between January and April, with the greatest number of cases in March. However, cases can occur from December through to early June. Cases in the winter or spring months, even in coastal districts, are rare.
When an outbreak occurs in unvaccinated cattle not previously exposed to the virus, a diagnosis of BEF can often be made based on clinical signs and the brevity of illness.
However, when most animals are immune and occasional cases occur, laboratory confirmation of the cause of illness may be required. Usually this is done by taking two blood samples - one during the very early stages of the illness, and another three weeks later. If BEF is responsible, BEF antibody levels will be much higher in the second test than in the first.
Medical treatment is often unnecessary for non-lactating stock. However, bulls and high producing cows in early to peak production should be treated promptly. Animals that have gone down should be provided with adequate shelter, water and food, as cattle left exposed in hot weather are much more likely to die.
They should be rolled over several times a day to help avoid loss of circulation to the underside limbs, which will result in permanent muscle damage. The heavier the animal is, the more critical it is to get it back on its feet as quickly as possible. Bulls, high producing dairy cows and other valuable stock that become recumbent should be treated as soon as they are found. Any animals that go down should be given a calcium injection as soon as possible. This will help them to rise.
The use of anti-inflammatory drugs is recommended for any animals that become recumbent, and would be useful for any clinically affected animals. This treatment is only available through veterinary prescription. Long withholding periods may apply to some anti-inflammatory drugs, so read the label carefully.
BEF can impair the swallowing reflex, so affected animals should not be drenched or force fed. This may result in the inhalation of food or water, which can cause pneumonia.
Once cattle have been infected with the disease, most are resistant to infection for many years or for life. However, some animals lose immunity after a few years, especially older animals.
Severe disease can occur in animals of any age that are introduced to districts where the disease is frequently observed from areas where the disease is uncommon.
Both live and inactivated vaccines against BEF are available:
- The live vaccine requires a veterinary prescription. It gives at least 12 months protection after two doses. The live vaccine is a freeze-dried preparation that must be kept frozen and then requires reconstitution immediately before use.
- The killed vaccine is a refrigerated bulk product like most other vaccines. It is easier to use and is cheaper, but only gives about six months protection.
With either vaccine, two doses are required four weeks apart to achieve adequate protection. Animals can be vaccinated from six months of age and should then be revaccinated each year to ensure continued protection.
The second dose of vaccine can be given only two weeks after the first, if protection is required urgently. This only gives 10 weeks of protection and not all animals are protected quickly. If the BEF season turns out to be a long one, a third vaccination will need to be given after 10 weeks to give longer lasting protection.
The choice of vaccine will depend on:
- the number of animals to be vaccinated,
- the predictability of BEF outbreaks in the region in question, and
- the farmers’ attitude to risk.
Some producers may decide to protect only their more valuable heavy animals, such as bulls and stud cows. Others may only vaccinate if BEF occurs in cattle to the north, or antibodies for BEF are detected in sentinel cattle close to their properties.
Due to the severe drop in milk production, vaccination is often worthwhile in dairy herds. Local knowledge of the frequency of outbreaks will assist decisions on the age of stock to be vaccinated. However, vaccination of bulls and very high producing cows is strongly recommended.
Vaccination in a commercial beef herd may or may not be worthwhile. It will depend on the stage of the management cycle when risk occurs. For example:
- Fever may cause heavily pregnant cows to abort if they are not protected.
- If steers are close to finished weights, the loss of condition if they are infected with BEF may make it economic to vaccinate (if given enough warning). If they are not close to market weight, vaccination may not be worthwhile.
Monitoring of arboviruses
NSW Agriculture and Local Land Services are involved in testing cattle for a National Arbovirus Monitoring Program (NAMP). Sentinel herds at various locations throughout Australia are blood sampled at regular intervals, to see if the cattle have been exposed to viruses carried by insects. Insect populations are also monitored by collections in special traps.
This allows animal health and quarantine authorities to demonstrate freedom from certain diseases to importing countries, to satisfy export requirements, and possibly give producers warning of the possible spread of disease south from endemic areas.
This Agfact is based on the first edition (1986) by R.W. Burton, Former Veterinary Officer (Epidemiology).
Bovine Ephemeral Fever - three-day sickness. Agfact A0.9.50, second edition 2001. Peter Kirkland, Principal Research Scientist, Elizabeth Macarthur Agricultural Institute, Menangle. Belinda Walker, Veterinary Officer, Gunnedah. Edited by Geof Murray, Job 2763