How to recognise and manage bovine ephemeral fever in cattle

Bovine ephemeral fever, widely known as three-day sickness, is a sudden viral disease of cattle and buffalo carried by biting insects. It appears mainly in warm, wet periods when those insects are active, and an outbreak can move through a herd within days. Affected animals show fever, weakness, stiffness, lameness and breathing difficulty, and milk production can fall sharply. Early recognition, insect control, vaccination where a suitable product is available, and prompt veterinary care are the measures that limit damage on a farm.

What the disease is

The virus belongs to the family Rhabdoviridae and the genus Ephemerovirus. It is arthropod-borne, meaning it is spread by biting insects rather than by ordinary contact between animals. Transmission by contact or fomites does not occur, so isolating a sick animal from the herd does not protect the others as it would with a contagious disease.

The disease occurs mainly in tropical and subtropical regions and has been reported across Africa, the Middle East, Australia and parts of Asia. Outbreaks follow the vector season, appearing in summer and particularly in wet periods, and they may stop abruptly with the onset of winter. Onset within a herd is rapid, with many animals affected within days or two to three weeks.

How it spreads, and why that matters for control

Both biting midges of the genus Culicoides and mosquitoes, including Culex and Anopheles species, are recognised vectors. The virus has been recovered from several Culicoides species and from anopheline and culicine mosquitoes caught in the field, but the identity of the principal vector has not been established, and evidence suggests that additional vector species remain to be identified.

That uncertainty has a practical consequence. Insect control aimed only at mosquitoes leaves a gap because Culicoides midges do not breed in standing water as mosquitoes do. They breed in damp organic material, muddy margins and manure-contaminated wet ground. A control programme should address both: standing water for mosquitoes and damp organic matter around sheds, water troughs, and drainage lines for midges.

Which animals are most at risk

Different age groups can be affected, though animals under six months are generally not susceptible. Heavy cows, bulls, high-yielding lactating animals, and pregnant heifers are the most vulnerable, and these are the groups to watch most closely during an outbreak.

That pattern also shapes the risk. Morbidity in an affected group may reach 80% or more, while overall mortality is usually low, commonly cited between 1% and 10%. The important qualification is that deaths occur only in the animals named above. Reported mortality rises considerably in mature, well-conditioned beef cattle and high-producing dairy cows, so a herd's best animals carry the greatest risk.

What to look for

The disease may present mainly with respiratory signs, with locomotor signs, or with a combination of both. Fever often occurs in two or more phases, so an animal may not be febrile at the time of examination, a common source of confusion.

Farmers may see sudden fever, shivering, loss of appetite, depression, watery eyes and clear nasal discharge. Drooling, raised heart rate, and rapid or laboured breathing may follow. Some animals develop bloat and reduced rumen movement. Lung emphysema and swelling under the skin may occur, including around the lower jaw or near the limb joints. Constipation appears in some animals and diarrhoea in others.

Stiffness and lameness can resemble acute laminitis. Severe weakness may progress to recumbency, at which point the animal can look much like a cow with milk fever. Abortion is also reported.

The virus enters the bloodstream and replicates in the vascular system, leading to repeated fever and inflammation of the joints and body cavities. That inflammation produces fibrin-rich fluid around the joints and within the cavities, which underlies the stiffness and difficulty rising.

Diagnosis, and what else it might be

Diagnosis rests on the clinical picture, supported where necessary by laboratory confirmation through seroconversion testing such as ELISA and serum neutralisation, and by post-mortem findings. Because a number of other conditions produce fever, breathing difficulty, weakness or recumbency, a suspected case should be assessed by a veterinarian rather than treated on assumption.

The differentials that matter are botulism, milk fever, pneumonia, haemorrhagic septicaemia, traumatic pericarditis, heat stress, and recumbency due to injury, such as a fracture or dislocation. A down cow or a cow struggling to breathe may need entirely different treatment depending on which it is, and treating the wrong one costs time the animal may not have.

Supportive care

Start supportive care early and contact a veterinarian. Provide complete rest, clean water, palatable feed, cooling, and clean dry bedding. Cool water applied over the animal, particularly over the head, helps bring the temperature down. Recumbent animals should be repositioned regularly to reduce prolonged pressure and muscle damage. Feeding, watering and milking should continue wherever it is safe to do so.

Anti-inflammatory treatment early in the course of disease is the mainstay, with non-steroidal anti-inflammatory drugs the usual choice. Antibiotics may be used to prevent or manage secondary bacterial infection. Calcium, most often as calcium borogluconate, may be given once the temperature has returned to normal, alongside antihistamines and other supportive measures. Drug choice, dose, route and withdrawal period are veterinary decisions and must follow the specific product label.

What not to do

This section matters as much as the treatment itself, because several instinctive responses make the animal worse.

Do not give oral fluids to an animal that cannot swallow properly, because pharyngeal paralysis may be present and the fluid will go into the lungs.

Be cautious with intravenous fluids, given the risk of worsening fluid accumulation in the lungs.

Avoid intravenous sodium bicarbonate, because affected animals tend towards alkalemia rather than acidosis, so bicarbonate pushes them further in the wrong direction.

Avoid aminophylline and etaphylline, because of the risk of alveolar rupture in lungs already emphysematous.

These are veterinary treatment decisions rather than things to improvise on farm.

Prevention

Vector control comes first, because biting insects are the source of infection. Reduce breeding sites for both groups of vector, meaning standing water for mosquitoes and damp organic material for midges, and use insect-control products according to local veterinary and label guidance. It is worth being realistic here: complete vector control is difficult in the regions where the disease is endemic, which is why vaccination carries much of the weight.

Vaccination is the second line and, in practice, the more dependable one. Killed vaccines provide roughly six months of protection, while live attenuated vaccines produce a longer-lasting antibody response, in some studies more than twelve months after two doses. Inactivated vaccines may need repeated administration before immunity is durable. Vaccination should be completed before the summer risk period rather than during an outbreak, and farmers should follow the instructions for the specific product available locally and their veterinarian's advice.

Animals that recover from natural infection develop long-lasting immunity, which is why repeat outbreaks in a herd tend to affect the younger animals born since the last one.

A checklist for the farm

Watch for sudden fever, shivering, reduced appetite, a sudden milk drop, stiffness, lameness or breathing difficulty.
Call for veterinary help early when several animals fall sick within a short period.
Remove or manage standing water where mosquitoes breed, and damp organic matter where midges breed.
Maintain insect control around sheds and animals through the vector season.
Keep sick cattle in a clean, dry, comfortable and well-cooled area.
Keep feed and water within easy reach when the animal can swallow safely.
Check recumbent cattle frequently and reposition them.
Include vaccination in the farm's prevention plan, timed ahead of the risk period.
Do not assume every fever, down cow or breathing problem is this disease, because other serious conditions look similar.
Use injectable medicines, antibiotics, vaccines and fluid therapy only on veterinary assessment, following product instructions and withdrawal periods.