Bluetongue disease
[3][6][7][8] Bluetongue outbreaks have had a significant economic impact, with estimated global losses reaching approximately 3 billion USD.
BTV also infects goats, cattle, and other domestic animals, as well as wild ruminants (for example, blesbuck, white-tailed deer, elk, and pronghorn antelope).
In cattle, constant changing of position of the feet gives bluetongue the nickname the dancing disease.
The current circulation of BTV-3 in Northern Europe is epidemiologically noteworthy due to the presentation of clinical signs in cattle and a higher sheep mortality rate than that observed with BTV-8.
[5][14][15] Other ruminants, such as goats, typically exhibit minimal or no clinical signs despite high virus levels in blood.
This abnormality is a condition in which the brain's cerebral hemispheres are like swiss cheese, or absent, and replaced by sacs filled with cerebrospinal fluid.
Subviral particles are probably akin to cores derived in vitro from virions by physical or proteolytic treatments that remove the outer capsid and causes activation of the BTV transcriptase.
The two remaining non-structural proteins, NS1 and NS2, are produced at high levels in the cytoplasm and are believed to be involved in virus replication, assembly and morphogenesis.
[19] Evidence suggests this is due to purifying selection across the genome as the virus is transmitted alternately through its insect and animal hosts.
This evolutionary process, in conjunction with the random fixation of quasispecies variants during transmission between susceptible animals and vectors, is postulated to be the primary driver of the genetic diversity observed in BTV field strains.
It is noteworthy that BTV serotypes 25 and higher are transmitted without midges, indicating that direct contact between sheep or goats may be a potential vector.
[3][11] The presence of the insect vectors determines the bluetongue disease's global distribution, with regions in Africa, Asia, Australia, Europe, North America, and other tropical/subtropical area being most affected.
Its occurrence is seasonal in the affected Mediterranean countries, subsiding when temperatures drop and hard frosts kill the adult midge vectors.
The relatively recent novel vector has facilitated a far more rapid spread than the simple expansion of habitats north through global warming.
[27] In September 2007, the UK reported its first ever suspected case of the disease, in a Highland cow on a rare-breeds farm near Ipswich, Suffolk.
[35][36] In 2023, Europe witnessed a series of notable epizootic occurrences at higher latitudes, partially attributable to the emergence of a novel serotype, BTV-3.
[37][38] Although the disease is not a threat to humans, the most vulnerable common domestic ruminants are cattle, goats, and especially, sheep.
[39] The spread of bluetongue to Southern, Central, and Northern Europe provides an illustrative example of the complex interactions between climate change, vector habitat suitability, animal population density, distribution, and movement, which collectively influence the patterns of disease emergence and transmission.
The recurrent emergence of novel strains and the occurrence of new outbreaks with significant socio-economic impacts highlight the urgent need for effective antiviral strategies.
The current vaccines for bluetongue virus (BTV) are serotype-specific, which limits their utility and has led to interest in host-targeted antiviral strategies that offer broader activity against multiple serotypes and a reduced risk of resistance development.
[7] Some available key measures include vector control, such as the use of insecticides, insect-proof nets, and improved housing to reduce exposure to biting midges.
Additionally, the removal of infected animals helps prevent further transmission by reducing the number of viremic hosts, while movement restrictions—including quarantines and health certifications—prevent the introduction of the virus to uninfected regions.
[49] The CVMP also adopted a positive opinion, recommending the granting of a marketing authorization for the veterinary medicinal product Syvazul BTV 3, suspension for injection, intended for sheep.
[50] The applicant for this veterinary medicinal product is Laboratorios Syva S.A.[50] Syvazul BTV 3 is a vaccine containing Bluetongue virus, serotype 3, BTV-3/NET2023, inactivated as active substance.
The English translation "Bluetongue" was initially proposed by Spreull[52] and derived from the Afrikaans term "bloutong," which refers to the condition of cyanosis of the tongue in clinically affected sheep.
[54] In 2021, a vessel owned by Khalifeh Livestock Trading and managed by Talia Shipping Line, both based in Lebanon, has been denied right to dock in Spain, as it has about 895 male calves suspected to be infected by bluetongue disease.
