Bluetongue
BTV, Bluetongue Disease
Occurrence
Bluetongue occurs almost worldwide. In 2023, a specific serotype of the virus, BTV-3, appeared for the first time in the Netherlands, Belgium and Germany. Since then, BTV-3 has spread further in Europe. Due to the absence of protective antibodies, livestock in regions not previously affected by BTV-3 are fully susceptible. A past infection with BTV-8 or BTV-4 or vaccination against these subtypes is not sufficient protection against infection with BTV-3. Further spread can therefore be assumed if this is not stopped by effective vaccination measures.
Host animals
Ruminants (e.g. cattle, sheep, goats), wild ruminants (e.g. deer, red deer, ibex, chamois) and camelids (e.g. alpaca). The sheep is considered the most susceptible animal species, although there are differences in susceptibility between the individual breeds. There is no risk of infection for humans.
Route of infection
The pathogen is transmitted by midges (biting-sucking insects). Direct transmission by smear infection from animal to animal is not known, but transplacental transmission (from the infected mother to the unborn young animal) can occur with certain BTV serotypes. The relevance of this vertical transmission for the epidemiology of the disease is unclear. Infectious BTV has been detected in the semen of infected bulls and rams. Transmission of field virus through mating or artificial insemination has not been confirmed. It has been shown that BTV can adhere to cattle embryos, but transmission through embryo transfer has not been observed. Contaminated needles from vaccination/injection equipment or surgical instruments pose a potential risk of transmission. There is no risk of bluetongue spreading or transmitting through meat or milk.
Symptomatology
The clinical picture is predominantly characterized by fever and hyperemic signs of congestion in the area of the head or the mucous membranes of the head (swollen, protruding "blue" tongue) and limbs. In most cases, sheep are more severely affected than cattle. In the latter and in goats, symptomless courses are also common. The clinical picture may resemble foot-and-mouth disease (e.g., fever, mucosal redness/inflammation, lameness). With the exception of sheep, mortality is low and also depends on the virus strain.
Control/prevention
An active surveillance programme is carried out annually in Austria to determine the absence of the pathogen. It is based on the division into 28 regions, the size of which takes into account topographical conditions, livestock density and political districts and subjects 60 unvaccinated cattle per region to a serological BTV antibody test. Insect repellents can also be used to prevent the transmission of the disease by midges. Midges fly to animals in open areas, especially between dusk and dawn. The competent authorities therefore recommend that animals be kept indoors during these periods.
Prevention
There are serotype-specific vaccines against bluetongue. There is currently an inactivated vaccine against serotypes 1, 2, 4 or 8 in sheep and cattle that is authorised in the EU (European Medicines Agency, EMA) (BTVPUR). This means that this vaccine may be used in Austria in accordance with Section 29 of the Animal Health Act 2024 (the attending veterinarian must notify the competent authority of the intended vaccination in good time; veterinarians must send annual reports on the vaccinations carried out to the competent authority). In addition, the Bluetongue Control Ordinance § 10 must be observed (vaccinated animals must have individual animal identification). There is currently no official vaccination programme against BT in Austria. Vaccination against bluetongue serotypes 1, 2, 4 or 8 is officially permitted, whereby this can be carried out on a voluntary basis at the request (and expense) of the livestock owner, as long as the framework conditions of the Animal Health Act and the Bluetongue Control Ordinance are complied with. This must be done in accordance with the provisions of Section 58 of the Veterinary Medicinal Products Act ("cascade") and Section 8 of the Medicinal Products Import Act.
There is currently no inactivated vaccine authorised by the EMA against serotype 3. There are 3 inactivated vaccines that have emergency authorisation in sheep and cattle in other EU countries. These vaccines were included in the Animal Vaccine Application Ordinance (Amendment 2024) and can be used in Austria in sheep and cattle under the conditions of Section 29 of the Animal Health Act 2024 and Section 10 of the Bluetongue Control Ordinance.
Situation in Austria
In September 2024, bluetongue reappeared in Austria for the first time since 2016. Serotype 4 was detected in two healthy cattle in Styria during routine testing. The discovery of BTV-4 in south-eastern Austria is surprising, as no such detections have been reported from neighbouring countries. Serotype 3 was also detected for the first time in Austria in another cow in Vorarlberg, this animal showed clear clinical symptoms. Further cases are to be expected due to the dynamic epidemiological situation. The status "free of bluetongue" has been suspended for the whole of Austria.
Ministry of Health: Information on the current bluetongue situation in Austria
Official monitoring is carried out annually in cattle, which is primarily based on the detection of antibodies against the bluetongue virus.
Austria has had "disease-free" status in accordance with Implementing Regulation (EU) 2021/620 since 15 April 2021. Austria had its first BT case with serotype 8 in 2008. In the second half of 2014, a new BTV-4 epidemic began in south-eastern Europe and spread rapidly from Turkey via Greece, Romania, Bulgaria and the Balkan states to Hungary and Croatia. In the course of this spread, serotype 4 was also detected in Austria for the first time on 17 November 2015. A total of four BTV-4 outbreaks were recorded in the provinces of Styria and Burgenland in 2015 and three outbreaks in the provinces of Burgenland and Carinthia in 2016. Freedom at WOAH was regained in February 2019.
Specialist information
Bluetongue was first detected in South Africa in 1934. The disease spread further with the export of Merino sheep to many countries on the African continent.
Bluetongue virus (BTV) is a non-enveloped double-stranded RNA virus that 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 ("distant" relationship, e.g. BTV-8 and BTV-15) between two BTV serotypes. Therefore, a BTV-vaccinated animal can 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 or after 15 minutes at a temperature of 60 °C. The virus can remain inactive for years under suitable conditions. The virus can survive for years under suitable conditions, e.g. in blood samples at 20 °C. (Source: OIE).
Differential diagnoses include FMD, BKF, BHV-1, BVD, PI-3, VS (vesicular stomatitis), EHD, cold sores, circulatory disorders of a different origin, etc.
Transmission
The pathogen is transmitted by so-called midges(Culicoides spp.); there is no direct transmission route from mammal to mammal. The infection is seasonally linked to the activity of the midges and therefore usually occurs in late summer and autumn. During the act of sucking on the infected animal, the midge ingests blood containing BTV. The BTV first enters the intestine and from there into the salivary glands of the midge. With the next sucking act, virus-containing saliva is introduced into the host's bloodstream. There the virus multiplies and spreads to all organs. After infection, the mammal builds up an immune response (antibody formation) against the pathogen. BTV can be detected in the midge for up to approx. 28 days, in sheep for up to approx. 60 days and in cattle for up to approx. 220 days.
Symptoms
Infected animals have a low mortality rate and high morbidity. The mortality rate (= proportion of the susceptible animal population that dies from 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, viraemia with fever and clinical symptoms occurs in the susceptible host. The most common form is the inapparent form. Different forms of progression have been observed in infected animals: acute, subacute and abortive, all beginning with a rise in temperature.
The symptoms are
- Fever (40-42 °C)
- Hyperaemia of the oral and nasal mucous membranes
- lip oedema
- hoof inflammation: Hyperaemia of the coronet band area
- abortions
- Changes in the skeletal musculature
Diagnostic
Suitable sample materials are:
- Blood (EDTA/serum)
- Milk
- Organs
- Mosquitoes
The detection of BTV from the above materials is possible with the following methods:
- Serological test methods for antibody determination: ELISA (serum and milk)
- Serum neutralization test (serum)
- Molecular biological identification (EDTA blood, organs and mosquitoes)
- BT virus cultivation (EDTA blood, organs, possibly mosquitoes)
In all cases, specimen shipment to the laboratory should ideally be performed with the addition of refrigerants and consideration of the appropriate transport regulations (UN3373) by a logistics company authorized to do so.
Contact
Institut für veterinärmedizinische Untersuchungen Mödling
- vetmed.moedling@ages.at
- +43 50 555-38112
-
2340 Mödling
Robert Koch-Gasse 17
Last updated: 02.10.2024
automatically translated