Akabane virus
Encyclopedia
The Akabane virus is an insect-transmitted
virus that causes congenital abnormalities of the central nervous systems in ruminant
s.
and infects the , specifically the calf's central nervous system (CNS) where it may cause varying amounts of damage. Affected calves may be blind, have difficulty in suckling, walking or learning herd behaviour, etc. Other species may become infected. These include buffalo
, camels, horses, sheep, goats and dogs. The disease
in these hosts is not commonly observed and, apart from in buffalo
, is probably not a particularly important infection.
Malformation of the joints, brain, spine and jaw are common in affected newborn animals. Abortion may also occur if damage to the fetus is severe.
brevitarsis." This, and the fact that the Akabane virus has been isolated from this midge
, has led to the supposition that it is C. brevitarsis which is responsible for the spread of the disease. Normally, in areas where the midge is prevalent, no signs of the disease is seen because the dams are immune. When suitable weather conditions (such as warm humid summers) prevail, the virus-carrying midge can extend its normal range into areas with susceptible animals. If these cattle have not previously been infected (often the younger animals) then it can be expected that the disease will make an appearance in the calving season.
in the blood of the calf or in the blood of the dam thanks to an ELISA
. Viral isolation can also be attempted with immunofluorescence
or PCR.
Treatment of Akabane disease, like most viral diseases, is impractical. In mild cases, the calf may be saved by assisting it in suckling, but it is rarely worth the trouble. Normal practice is to destroy the affected calf.
Vaccination is used to control the spread of disease. Control of the insect vectors is advisable if possible, but often difficult to implement.
Arbovirus
Arbovirus is a term used to refer to a group of viruses that are transmitted by arthropod vectors. The word arbovirus is an acronym . Some arboviruses are able to cause emergent disease.-Transmission:...
virus that causes congenital abnormalities of the central nervous systems in ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s.
Virus
Two viruses, both arthropod borne, have been implicated in the cause of these congenital defects: Akabane virus, named after the district in Japan where it was first found, and Aino virus. Generally, both these viruses are referred to as Akabane virus.Disease
Akabane virus does not, as far as is known, cause any overt sign of disease, in either young or adult animals. Its effect is on the fetus and the conditions which result in the disease in the fetus may be summarised as follows- 1. The pregnant dam has not previously had exposure to the virus and therefore has no specific immunity and becomes infected, and 2. The virus passes through the placentaPlacenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
and infects the , specifically the calf's central nervous system (CNS) where it may cause varying amounts of damage. Affected calves may be blind, have difficulty in suckling, walking or learning herd behaviour, etc. Other species may become infected. These include buffalo
Bubalus
Bubalus is a genus of bovines, whose English name is buffalo. Species that belong to this genus are:* Subgenus Bubalus** Water Buffalo, Bubalus bubalis*** Carabao, Bubalus bubalis carabanesis...
, camels, horses, sheep, goats and dogs. The disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
in these hosts is not commonly observed and, apart from in buffalo
Bubalus
Bubalus is a genus of bovines, whose English name is buffalo. Species that belong to this genus are:* Subgenus Bubalus** Water Buffalo, Bubalus bubalis*** Carabao, Bubalus bubalis carabanesis...
, is probably not a particularly important infection.
Malformation of the joints, brain, spine and jaw are common in affected newborn animals. Abortion may also occur if damage to the fetus is severe.
Infection
As Akabane is an infectious disease, it is necessary to know how the virus is transmitted if the infection is to be combatted. It has been shown that animals that have been infected with Akabane virus are found mostly in those parts of Australia which have the blood sucking midge "CulicoidesCulicoides
Culicoides is a genus of biting midges in the subfamily Ceratopogonidae. Around 500 species of Ceratopogonidae are at present placed in the genus and this is split into many subgenera. Several species are known to be vectors of various diseases and parasites which can affect animals.-Notable...
brevitarsis." This, and the fact that the Akabane virus has been isolated from this midge
Midge
A midge is a very small, two-winged flying insect. "Midge" may also refer to:-Real:* Midge Costanza , American politician* Mildred Gillars , aka "Midge", American broadcaster of Nazi propaganda during World War II...
, has led to the supposition that it is C. brevitarsis which is responsible for the spread of the disease. Normally, in areas where the midge is prevalent, no signs of the disease is seen because the dams are immune. When suitable weather conditions (such as warm humid summers) prevail, the virus-carrying midge can extend its normal range into areas with susceptible animals. If these cattle have not previously been infected (often the younger animals) then it can be expected that the disease will make an appearance in the calving season.
Diagnosis and treatment
Diagnosis can often be made on the basis of clinical signs and can be confirmed by demonstration of antibodyAntibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
in the blood of the calf or in the blood of the dam thanks to an ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
. Viral isolation can also be attempted with immunofluorescence
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
or PCR.
Treatment of Akabane disease, like most viral diseases, is impractical. In mild cases, the calf may be saved by assisting it in suckling, but it is rarely worth the trouble. Normal practice is to destroy the affected calf.
Vaccination is used to control the spread of disease. Control of the insect vectors is advisable if possible, but often difficult to implement.
Conclusion
Akabane disease is an important disease in those areas which are subject to only an occasional influx of C. brevitarsis. It is a useful method for obtaining information about the spread and persistence of C. brevitarsis which may be a possible vector for the insect borne viral disease "Bluetongue" - should Bluetongue ever enter Australia.Cases of outbreaks
Nearly all cattle breeders in the northern part of Australia, including north-eastern New South Wales, have experienced congenital defects in calves, and more specifically, those congenital defects that give rise to calves known as curly, imbecile, silly or dummy calves. A small percentage of these are, no doubt, the result of non-infectious causes, perhaps inherited or the result of some effect during gestation.External links
- Merck veterinary manual
- www.scienceimage.csiro.au/index.cfm?event=site.image.detail&id=1310
- Couch A.J. (1984) Akabane Virus. Australian Red PollRed PollThe Red Poll is a dual purpose breed of cattle developed in England in the latter half of the 19th century.-Description and uses:The cattle are red, preferably deep red with white only on the tail switch and udder. They are naturally polled...
Society Newsletter 92: 22-23