Bovine Ephemeral Fever

Also known as

Three-day fever, three-day stiffness, bovine epizootic fever, dragon foat disease, lazy man’s disease, bovine influenza, styfsieket,dengue of cattle

Description

Bovine ephemeral fever was first reported in the late 19th century.  This is a viral disease of cattle and water buffalo, spread by biting insects. It causes a drop in milk production, reproductive losses, weakness, and sometimes death.

This noncontagious, viral disease of cattle and water buffalo is seen in Africa, the Middle East, Australia, and Asia. The disease has not been reported in North or South America or in Europe.

Infection with no obvious signs can develop in Cape buffalo, hartebeest, waterbuck, wildebeest, deer, and possibly goats, sheep, and gazelles. Low levels of antibody have been recorded in several other antelope species, giraffe, and even in pigs and elephants, but domestic cattle are most adversely affected.

Recovery of sick animals can be prolonged in some individuals. Mortality is typically low (only 1 to 2% of animals affected), but significantly higher fatality rates were reported in some recent outbreaks.

Bovine ephemeral fever can occur as localized outbreaks or in seasonal epizootics (temporary but widespread instances of disease) that sweep across broad geographic areas. Seasonal patterns can vary with the region, depending on environmental factors that favor multiplication of biting insects.

In some areas, outbreaks tend to be associated with high rainfall, since moisture promotes higher populations of insects. When weather is dry, bovine ephemeral fever has been seen in cattle gathered around sources of water.

Outbreaks usually end with the first heavy frosts in temperate climates. In other areas, cases may decrease or end during the dry season—whenever insect populations dwindle.

The morbidity rate (amount of animals affected in a group) is highly variable, depending on their previous exposure, the age of the animals, and other factors. Morbidity rate can approach 100% in some outbreaks, or be as low as 1-10% in others. Clinical signs are usually more severe in adult animals than calves; signs of infection are rare in cattle less than 6 months of age, even when they have no maternal antibodies from colostrum.

Bulls, animals in good condition (such as fat steers) and high-producing cows are more severely affected; mortality rates up to 10 to 30% have been reported in these animals. Overall, the mortality rate is usually low, but sometimes 2 to 20%, and occasionally higher during some recent outbreaks in the Middle East and Asia. Why deaths were more common in these outbreaks is unknown.

Buffalo are thought to be less severely affected than cattle. However, severe outbreaks can be seen, and mortality was reported to be 5% during one outbreak in buffalo.

The prevalence, geographic range, and severity of the disease can vary from year to year, and epidemics occur periodically. During epidemics, onset of clinical signs is rapid; many animals are affected within a few days or weeks.

Bovine ephemeral fever is most prevalent in the wet season in the tropics and during summer to early autumn in the subtropics or temperate regions; it disappears abruptly in winter. Virus spread can be associated with wind (which can carry biting insects to different locations) and transportation of animals.

Clinical signs vary in individual animals, but the classic course begins with a fever, which is often variable during the day. Temperature peaks typically occur 12 to 18 hours apart. In lactating cows, milk production often drops dramatically during the first fever spike. T

here are often very few other clinical signs at this time, although some animals may be depressed, stiff or reluctant to move. However, the illness soon becomes more obvious; most animals stop eating and are dull and depressed, with increased heart rate, rapid breathing, and nasal discharge (clear or thick with mucus).

Profuse salivation, muscle twitching, muscle weakness (which may be temporary or permanent), waves of shivering, or watering eyes may also be seen. Some animals develop swelling of the salivary glands or swelling around the eyes, or patchy swellings on the head.

Shifting lameness, stiffness and joint pain are common; the joints may or may not be swollen. Lameness can be severe enough to look like a fracture or dislocation. Labored breathing and rattling lung sounds may be evident in severe cases.  A few animals abort.

Many animals, particularly fatter individuals, become recumbent for periods that range from 8 hours to several days or more. Most animals lie in sternal recumbency (upright on the breastbone), but in severe cases, animals may become laterally recumbent (flat on their sides).

Some animals temporarily lose their normal reflexes and are unable to get up. Recumbent animals may be bloated because the rumen stops working (and they no longer chew the cud), or constipated (or more rarely, develop diarrhea), or lose their swallowing reflex.

Clinical signs can be made worse by severe environmental stress or forced exercise. Mild disease may be exacerbated by hot weather that causes dehydration. Disease is milder in young than in mature animals, in lean than fat animals, in light steers and cows than in bulls, and in dry cows compared with those in heavy lactation.

Most animals begin to improve a day or two after the initial signs, and most recover completely within another one or two days. Lactating cows, bulls and fat animals take up to a week to recover. Animals generally lose condition rapidly during the illness, and regain their weight very slowly.

Complications are uncommon in most outbreaks, but can include temporary or (more rarely) permanent paralysis, as well as gait impairment, aspiration pneumonia, emphysema, mastitis, and accumulation of air under the skin along the back.

Many of these complications may be the result of trauma or complications of spending so much time lying down. Temporary infertility (up to 6 months) can develop in affected bulls, as a result of the severe fever that accompanies acute infection. Permanent infertility is rare.

In lactating animals that become ill and recover, milk production is generally decreased for the rest of the lactation, but usually returns to normal after subsequent pregnancies. When cows are infected early in lactation, it may take weeks before they return to relatively normal production. If cows are infected in mid-lactation, they may not return to milk production during that lactation.

Cows in late pregnancy may abort. In severe cases, there may be temporary or permanent paralysis of all limbs, inability to swallow, and drooling. After 1 to 4 days, these animals suffer loss of reflexes, and may slip into a coma, and die.

Whether the disease is mild or severe, in the animals that survive, recovery begins quite suddenly and is complete in 95 to 97% of uncomplicated cases, giving rise to the name “ephemeral fever.” Although mortality is usually less than 1%, the most productive mature animals are the ones most often lost, plus there are losses of milk production, abortion losses, and temporary infertility in bulls.

Other losses include fatal pulmonary emphysema, pneumonia, mastitis, and locomotor disturbances. The total economic loss in an outbreak can be severe.

Death is uncommon, but may occur during either the fever stage or during convalescence. During recent outbreaks in China, some severely ill cattle died with signs of labored breathing, only 6 to 12 hours after they first became ill. Secondary complications such as pneumonia or trauma are thought to contribute significantly to the death rate. Subclinical infections are also seen.

Water buffalo have similar signs. The disease is usually thought to be milder in this species; however, some severe outbreaks have been reported. Experimentally infected sheep showed no signs of illness.

Signs of bovine ephemeral fever in cattle appear suddenly and vary in severity. Some may become recumbent and paralyzed for as brief as 8 hours or as long as 1 week. There are some reports of abortions. This might be an indirect consequence, because this virus does not seem to cross the placenta or affect the fertility of the cow.

Definitive diagnosis is obtained by PCR tests in a laboratory.

Signs

• Recurring fever (104°–107.6°),
• Shivering,
• Lack of appetite,
• Watering eyes,
• Nasal discharge,
• Drooling,
• Shortness of breath and difficult breathing,
• Rapid breathing,
• Increased heart rate,
• Depression,
• Stiffness and lameness,
• Sudden decrease in milk yield

Cause

Bovine ephemeral fever is caused by bovine ephemeral fever virus (BEFV), a member of the genus Ephemerovirus in the family Rhabdoviridae. At least 4 subtypes have been identified, but there is only one serotype. Some closely related viruses, such as kotonkan virus, may cause similar illnesses. Additional ephemeroviruses and unclassified rhabdoviruses (Adelaide River virus, Kimberley [Malakal] virus, Berrimah virus, Puchong virus, Yata virus, Koolpinyah virus, Obodhiang virus) are not known to cause disease in domesticated animals.

BEFV appears to be transmitted by biting insects, but the identity of the vector or vectors is not clear. This virus has been isolated from various mosquitoes, and from a number of Culicoides species (biting midges). Laboratory observations, and evidence of the disease from some locations, currently suggest that mosquitoes are the primary vectors.

However, there are some indications that Culicoides might be significant vectors in parts of Africa such as Kenya. Windborne transmission of infected vectors has been suspected in some outbreaks.

There is no evidence that bovine ephemeral fever can be transmitted directly between animals; this disease is not spread by close contact, body secretions, or aerosol droplets, and is rapidly inactivated in carcasses after death.

Transmission by contact or fomites (objects or materials) does not occur. The virus does not appear to persist for long periods in recovered cattle, but the infection does result in long-term immunity.

The incubation period is thought to be 2-4 days in most cases, with a maximum of 10-11 days.

Diagnosis of bovine ephemeral fever is based almost entirely on clinical signs in an epidemic. For a lab test, whole blood should be collected from sick and apparently healthy cattle in affected herds. Timely laboratory confirmation is mostly performed by PCR and rarely by virus isolation. A 4-fold rise in antibody titer between two blood samples collected 2 to 3 weeks apart confirms infection.

Mortality is usually low when sick animals receive appropriate medical care. Economic losses mainly result from significant decrease in milk production in dairy cattle and loss of condition in beef cattle.

Prevention

Bovine ephemeral fever is preventable. Primary vaccination in calves followed by regular boosters with high-quality vaccine usually provides satisfactory protection. Whether the susceptible populations are vaccinated, and which populations and individuals need to be vaccinated, depend on the disease prevalence in the area, the value of animals, and sometimes, the risk assessment and control measures of the authorities.

Vector control may be helpful, but whether it is practical (and its effectiveness in BEF control) may be difficult to evaluate.

Disease reporting and quick response is vital for containing outbreaks in disease-free regions. Veterinarians who encounter or suspect bovine ephemeral fever should follow their national and/or local guidelines for disease reporting. In the U.S., state or federal veterinary authorities should be informed immediately.

Because illness and viremia (presence of the virus in the blood) are both transient, and carriers are not known, a short quarantine in vector-free facilities should prevent the introduction of BEF in transported animals. If an outbreak occurs among imported animals in a small area, placing them in an insect-proof seclusion area and treating the premises with insecticides has a chance of success.

In endemic areas, vaccination is generally utilized to prevent disease, particularly in lactating cattle and bulls. Vaccines are not necessarily employed in regions where outbreaks occur regularly, because most animals develop immunity before they become adults.

Vaccination is more often used in the face of an outbreak. Moving valuable animals into insect-proof facilities may be considered during outbreaks or in high risk seasons.

There is conflicting evidence regarding the effectiveness of the commercially available attenuated or inactivated BEF vaccines. Although an attenuated BEF vaccine showed high effectiveness in Australia, reports from other countries indicate lower effectiveness of the same vaccine. Inactivated virus vaccines have not produced long-term protection against experimental challenge with virulent virus and cannot guarantee lasting immunity.

In field studies, these vaccines were 50% effective only after at least three vaccinations. Although a subunit vaccine that protects against field and laboratory challenge has been described, it is not commercially available. The efficacy of vector control remains uncertain, because the insect vectors have not been fully identified.

Treatment

Treatment includes administration of non-steroidal anti-inflammatory drugs, along with supportive care of recumbent cows.

Complete rest is the most effective treatment for bovine ephemeral fever, and recovering animals should not be stressed or worked because they may relapse. Anti-inflammatory drugs given early and in repeated doses for 2 to 3 days are effective.

Oral dosing with fluids should be avoided unless the swallowing reflex is functional (unless fluids are given via nasogastric tube (into the nostril and down to the stomach, rather than through the mouth).

Cattle with signs of hypocalcemia (low calcium levels, rumen shutdown, muscle weakness, loss of reflexes) are treated with calcium borogluconate injections, as you would treat a case of milk fever.

Antibiotic treatment to control secondary infection and rehydration with fluids (containing the proper balance of electrolytes) may be necessary. Treatment may be unnecessary in mild cases, but more severely affected animals are often treated, particularly when they have become recumbent. Some animals with a more prolonged course of disease were not responsive to treatment, however during recent outbreaks in Taiwan.

Good nursing can usually aid recovery. Recumbent animals should be provided with water, food and shelter if necessary, but animals should not be forced to stand or move. Laterally recumbent animals (flat on their sides) should be rolled periodically to prevent loss of circulation and muscle damage on the side they are lying on.