Ministry of Health: Legislation Bluetongue
Bluetongue was first detected in South Africa in 1934. With the export of merino sheep to many countries on the African continent, the disease spread further.
Bluetongue Virus (BTV) is a non-enveloped double-stranded RNA virus and belongs to the genus Orbivirus of the family Reoviridae. The serological relationship between the numerous individual BTV serotypes varies. For this reason, it is possible that there is either a high cross-reaction ("close" relationship, e.g. BTV-8 and BTV-18) or a low cross-reaction ("wide" relationship, e.g. BTV-8 and BTV-15) between two BTV serotypes. Therefore, a BTV-vaccinated animal may become clinically ill with another BTV serotype and produce antibodies against this second BTV serotype. In laboratory tests the bluetongue virus became inactive after 3 hours at a temperature of 50 °C and after 15 minutes at a temperature of 60 °C. The virus can survive for years under suitable conditions, e.g. in blood samples at 20 °C. (Source: OIE).
Differential diagnoses include foot-and-mouth disease, BKF, BHV-1, BVD, PI-3, VS (vesicular stomatitis), EHD, lipgrind, circulatory disorders of other origin, etc.
Mode of transmission
The pathogen is transmitted by mosquitoes (Culicoides spp.), i.e. there is no direct transmission route from mammal to mammal. Since mosquitoes are involved in the spread of viruses, the disease is seasonally linked to the activity of Culicoides mosquitoes. Disease cases occur seasonally, mostly in late summer and autumn, when the mosquito feed from the infected animal and absorbs BT virus-containing blood. The bluetongue virus (BTV) first enters the intestine and from there continues into the salivary glands of the mosquito. With the next feeding act, saliva containing BT virus is introduced into the mammal's (ruminant) bloodstream. The virus multiplies and spreads to all organs. After infection, the mammal builds up an immune response (antibody formation) against the pathogen. The BT virus can be detected in mosquitoes up to approx. 28 days, in sheep up to approx. 60 days and in cattle up to approx. 150 days.
Infected animals have a low mortality and high morbidity rate. Mortality (= proportion of the susceptible animal population that dies of the disease) is described as 1% to 5% in sheep, and up to 1.5% in goats and cattle. after the bite of an infected mosquito, the susceptible host develops viremia with fever and clinical symptoms. The most frequent form of the disease is inapparent. In diseased animals, various forms of progression have been observed: acute, subacute and abortive, all of which begin with a rise in body temperature.
The symptoms are:
- fever (40-42 °C)
- Hyperemia of the oral and nasal mucous membranes
- Lip edema
- Clauditis: Hyperemia of the coronary region
- Changes in the skeletal musculature
After the first cases of BTV-4 were detected in the south-east of Austria, the surveillance programme was adjusted to precisely limit the extent of BT virus circulation. For this purpose, a monitoring scheme was used which was already in use during the BTV-8 epidemic in 2008. 28 regions, whose size takes into account topographical conditions, livestock density and political districts, were defined and 60 unvaccinated cattle per region were subjected to a serological BTV-antibody test in addition to the already ongoing surveillance. After two years without a BTV case in south-eastern Austria, the BTV-4 restriction zone was reduced and lifted again in December 2018.
In addition, Austria uses a vector surveillance programme to obtain information on the occurrence and periods of activity of virus-transmitting insects (mosquito species of the genus Culicoides spp.). The results of that programme are used to declare seasonal vector-free periods. Mosquito traps are installed at selected locations and temperature monitoring is carried out at the same time to ensure that no vector activity is to be expected. This provides the animal trade with additional movement options.
There are serotype-specific vaccines against Bluetongue virus. Since 01.08.2008 an inactivated BTV-8 vaccine for cattle and small ruminants has been approved by the EMEA. Currently, no official vaccination programme against BT irus is carried out in Austria. Vaccination against bluetongue virus serotype 4 is permitted, although this can be carried out on a voluntary basis at the request (and cost) of livestock owners. However, as bluetongue is a notifiable disease under the Animal Diseases Act, certain framework conditions must be complied.
Suitable sample materials are
- Blood (EDTA/serum)
The detection of BTV from the above materials is possible using the following methods:
- Serological tests for antibody detection: ELISA (serum and milk)
- Serum neutralisation test (serum)
- Molecular biological identification (EDTA blood, organs and mosquitoes)
- BT virus cultivation (EDTA blood, organs, possibly mosquitoes)