Bovine Ephemeral Fever
Also Known As: BEF — Dengue Fever — Lazy Man’s Disease — Stiff Sickness — 3 day Sickness — Dragon Boat Disease — Vil — Bovine Epizootic Fever — Stiffsiekte (South Africa)
Caused By: Bovine Ephemeral Fever Virus — BEFV
Introduction
Bovine Ephemeral Fever is a viral disease causing fever, dehydration, gastrointestinal, reproductive and neurological disease in cattle. The pathogen involved is a rhabdovirus.
Due to its geographical distribution and association with heavy precipitation, BEF often occurs simultaneously with epizootics of Rift Valley Fever.
BEF is not zoonotic.
This disease is notifiable to the World Organisation for Animal Health (OIE).
Distribution
The virus occurs in Asia, Africa, Australia and Pacific islands. It is transmitted by a range of insect vectors including mosquitoes and midges. This is the ONLY route of disease transmission.
Signalment
Cattle and buffalo appear to be the only natural host of BEF. The disease is more severe in fat, lactating and heavily pregnant cows and bulls/steers.
In tropical regions, disease occurs in the wet season, while in temperate countries, it tends to present throughout Spring, Summer and Autumn.
When outbreaks occur annually or semi-annually, younger animals tend to be infected and so the economic impact is often less. Hence, the less frequent epidemics are, the more severe they tend to be.
Clinical Signs
The main clinical signs are very high fever, dehydration and animals often refuse to drink. Many signs are attributable to the hypocalcaemia caused by BEF.
Lymphadenopathy may be a feature as well as stiffness and lameness in the limbs with tremors/spasms and possible recumbency.
Gastrointestinal disease may present as hypomotility and constipation or diarrhoea. Pregnant cattle may abort and infertility can occur in either sex. Cows may develop agalactia.
Other signs may include dullness, depression, lethargy and coma in severe cases. Some animals develop respiratory disease and subcutaneous emphysema, oedema and crepitation.
Hot weather increases mortality in epidemics.
Mild cases - <18mo old, ocular and nasal discharge, lameness, inappetance, fever, recovery in 1-2days.
Moderate – Severe depression, recumbency, respiratory signs, salivation and dehydration, rumenal atony, milk reduction.
Severe – lateral recumbency, paralysis, reflex loss, subcutaneous emphysema, tachycardia and tachypnoea, mortalities. Residual paralysis may remain after resolution of fever.
Viraemia usually lasts 3-5 days after which recovery and natural immunity are life-long.
Diagnosis
Diagnosis is often based on clinical observations of various stages of disease present simultaneously and history of sudden onset outbreaks on the farm or neighbouring units.
Isolation of virus from blood taken during pyrexic phase is most efficient laboratory method of diagnosis. The virus can be identified by immunofluorescence or immunostaining.
A rising antibody titre when sampled during fever and 2 weeks later is also confirmatory.
On post-mortem, only generalised inflammatory changes are evident with neutrophilic infiltration of tissues and muscle necrosis. Straw coloured fibrinous fluid is often present in several cavities.
Treatment
Calcium borogluconate and/or NSAIDs will resolve many clinical signs and reduce pyrexia. All should be injected as swallowing reflex may be dysfunctional.
Draught cattle need rest for at least one week after recovery or further mortalities may occur.
Control
Vaccines are available in Japan, Australia and South Africa. Annual boosters are essential to maintain immunity. All are too expensive for use in developing countries.
Vector control is theoretical and almost impossible. Quarantine also has no impact upon local spread due to vector transmission. Movement regulations vary with country and time and should be adhered to.
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References
Animal Health & Production Compendium, Bovine Ephemeral Fever datasheet, accessed 16/06/2011 @ http://www.cabi.org/ahpc/
Animal Health & Production Compendium, Bovine Ephemeral Fever Virus datasheet, accessed 16/06/2011 @ http://www.cabi.org/ahpc/
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