Editing Bluetongue disease (section)

== Clinical signs ==
[[File:FCO-brebis.jpg|thumb|Infected sheep]]
[[File:Bluetongue in Captive Yak.png|thumb|A domestic [[yak]] is infected with Bluetongue virus. The tongue is swollen, cyanotic, and protruding from the mouth.]]
In sheep, BTV causes an acute disease with high morbidity and mortality. BTV also infects goats, cattle, and other domestic animals, as well as wild [[ruminants]] (for example, [[blesbuck]], [[white-tailed deer]], [[elk]], and [[pronghorn antelope]]).<ref name="Saminathan_2020" /><ref name = roy/> The clinical signs are summarized under the term FFF (fever, face, feet).<ref name="Wageningen_University">{{Cite web |website=Wageningen University & Research |date=2024-12-12 |title=Bluetongue |url=https://www.wur.nl/en/research-results/research-institutes/bioveterinary-research/animal-diseases/virology/bluetongue-1.htm |access-date=2024-12-12 |language=en-us}}</ref>

Major [[sign (medicine)|signs]] are high fever, excessive [[saliva]]tion, [[edema|swelling]] of the face and tongue, and [[cyanosis]] (in severe conditions) of the tongue.<ref name="WOAH" /> Swelling of the lips and tongue gives the tongue its typical blue appearance, though this sign is confined to a minority of the animals. Nasal signs may be prominent, with nasal discharge and [[stertorous]] respiration.

Some animals also develop foot lesions, beginning with coronitis, with consequent lameness. In sheep, this can lead to knee-walking. In cattle, constant changing of position of the feet gives bluetongue the nickname '''the dancing disease'''.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/uk/7019511.stm |title='Dancing' disease set for long run |work=[[BBC News]] | vauthors = McGrath M |date=29 September 2007 |access-date=2008-10-24}}</ref> Torsion of the neck ([[opisthotonos]] or [[torticollis]]) is observed in severely affected animals.

Not all animals develop signs, but all those that do lose condition rapidly, and the sickest die within a week. For affected animals that do not die, recovery is very slow, lasting several months.

The [[incubation period]] is 5–20 days, and all signs usually develop within a month. The [[mortality rate]] is normally low, but it is high in susceptible [[breed]]s of sheep. In Africa, local breeds of sheep may have no mortality, but in imported breeds, it may be up to 90%.<ref>{{cite book |title=Handbook on Animal Eiseases in the Tropics |date=1976 |publisher=British Veterinary Association |location=London |isbn=978-0-901028-10-5 |edition=3rd}}</ref>

The manifestation of clinical signs in cattle is contingent upon the strain of virus. BTV-8 has been documented to cause a severe disease state and mortality in cattle. 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.<ref name="WOAH" /><ref>{{cite journal | vauthors = Conraths FJ, Gethmann JM, Staubach C, Mettenleiter TC, Beer M, Hoffmann B | title = Epidemiology of bluetongue virus serotype 8, Germany | journal = Emerging Infectious Diseases | volume = 15 | issue = 3 | pages = 433–435 | date = March 2009 | pmid = 19239757 | pmc = 2681128 | doi = 10.3201/eid1503.081210 }}</ref><ref>{{cite journal | vauthors = van den Brink KM, Santman-Berends IM, Harkema L, Scherpenzeel CG, Dijkstra E, Bisschop PI, Peterson K, van de Burgwal NS, Waldeck HW, Dijkstra T, Holwerda M, Spierenburg MA, van den Brom R | title = Bluetongue virus serotype 3 in ruminants in the Netherlands: Clinical signs, seroprevalence and pathological findings | journal = The Veterinary Record | volume = 195 | issue = 4 | pages = e4533 | date = August 2024 | pmid = 39148262 | doi = 10.1002/vetr.4533 | doi-access = free }}</ref> Other ruminants, such as goats, typically exhibit minimal or no clinical signs despite high virus levels in blood. Therefore, they could serve as potential virus reservoirs of BTV.<ref name="Saminathan_2020" /> [[Red deer]] are an exception, and in them the disease may be as acute as in sheep.<ref>{{cite book |title=Diseases of Sheep |vauthors=Jensen R, Swift BL |date=1982 |publisher=Lea and Febiger |isbn=978-0-8121-0836-1 |location=Philadelphia}}</ref>

Lamb infected in utero can develop congenital [[hydranencephaly]]. 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]].  Ewes infected with bluetongue virus while pregnant can have lambs with this defect, as well as giving birth to lambs who are small, weak, deformed or blind. These affected lambs die within a few days of birth, or are born dead.