BLUE TONGUE BY Fatma Khalifa Synonyms Sore mouth

BLUE TONGUE BY Fatma Khalifa

Synonyms • Sore mouth • Sore muzzle • Ovine catarrhal fever

Defination It is a non contagious , insect-borne, viral disease of ruminants mainly sheep and less freqently cattle, goats, buffalo , deer, camelids (camels, llamas, alpacas, guanaco and vicuña). and antelope. It is caused by Bluetongue virus (BTV). The virus is transmitted by the midges Culicoides imicola , Culicoides variipennis and other Culicoides.

Eitology It caused by : blue tongue virus Orbivirus genus Reoviridae family It is douple stranded RNA virus surrounded by two protein shells. • The two outer capsid proteins, VP 2 and VP 5, mediate attachment and penetration of BTV into the target cell. • 27 distinct serotypes. • • •

Eitology • The virus makes initial contact with the cell with VP 2, triggering receptor-mediated endocytosis of the virus. • The low p. H within the endosome then triggers BTV's membrane penetration protein VP 5 to undergo a conformational change that disrupts the endosomal membrane.

Eitology • Bluetongue virus does not survive outside the insect vectors or susceptible hosts. • Survival of the virus within a location is dependent on whether the vector can overwinter in that area. • There are many different strains (serotypes) of Bluetongue with each given a number (currently up to 27).

Transmission It is spread by insects called biting midges (Culicoides spp. ).

Transmission • It transmitted by insect Venereal transmission • (vector). Other biting insects, such as ticks or sheep keds, may also transfer the virus. • It is not spread by contact between animals. • Animal carcasses and products such as meat and wool are not a method of spread.

Epidemological patterns • prefer warm, moist conditions and are in their greatest numbers and most active after rains. • Peak of midge populations occur during the late summer and autumn in Europe and therefore this is the time when Bluetongue is most commonly seen. • The midges can be carried very large distances on the wind (over 200 km) and this has been the primary way Bluetongue serotypes are introduced into new areas. • Viral survival and vector longevity is seen during milder winters. • Animals that recover from infection with one serotype will be immune to that strain but not to others.

Susceptible • Natural host : Sheep ( most severly affected species). • Other ruminants are rarely affected Which not develop to clinical signs and act as resvoir as well as cattle are the main mammalian reservoir of the virus and are very important in the epidemiology of the disease. • Humans are not affected.

Susceptible host • Domestic dogs in the long-distance spread of bluetongue virus (BTV) remains unproven. It is currently known that dogs are capable of being infected with BTV, can mount an antibody response to the virus and in some cases die showing severe clinical signs of disease.

Geographical distribution • Confined to tropical and subtropical areas. • now exist in Africa, Europe, the Middle East, North and South America and Asia as well as on islands such as Australia, • Mediterranean countries, subsiding when temperatures drop and hard frosts kill the adult midge vectors.

Pathogensis

Pathogensis Bite of vector Local lymph nodes 1 st Viraemia Other L. N. , spleen &bone marrow Endothelial cell Multiplication 2 nd Monocyte and macrophage Tissue of fetus

Clinical signs • The clinical signs of Bluetongue, are vary depending upon viral strain and sheep breed. • The incubation period is 5– 20 days, and all signs usually develop within a month. • High rectal temperature ( up to 42. 0°C ). • Eye and nasal discharges (range from serous to mucopurulent). • Drooling as a result of ulcerations in the mouth. • Swelling of the mouth, head and neck. • Swelling of the lips and tongue gives the tongue its typical blue appearance,

Clinical signs • Difficulty breathing due to pulomary edema. • Affected sheep showing arched back with the neck extended and the head held lowered. • Erosions may appear on the lips progressing to ulcers. 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.

Clinical signs • Lameness with inflammation at the junction of the skin and the coronary band. • Abortion

Clinical signs swelling of the face and ears and the sheep often appears stiff and reluctant to move. Early clinical case of BTV showing depressed appearance.

Clinical signs Facial oedema and nasal discharge and excoriation of BTV in infected sheep.

Clinical signs Serous to mucopurulant nasal discharge Affected cattle are febrile (up to 40. 0°C) and appear stiff due to swelling of the coronary band at the top of the hooves

clinical signs Multiple pinpoint haemorrhages in the skin around the bases of the teats.

Clinical signs Focally extensive area of haemorrhage (with associated ulceration not clearly visible in this image) on the ventral surface of the tongue. There are multifocal pinpoint haemorrhages covering most of the ventral surface of the tongue

Clinical signs • The mortality rate is normally low, but it is high in susceptible breeds of sheep. • In Africa, local breeds of sheep may have no mortality, but in imported breeds it may be up to 90 percent. • In cattle, goats and wild ruminants infection is usually asymptomatic despite high virus levels in blood. • Red deer are in exception, and the disease may be as acute as in sheep

Economic importance • Bluetongue virus infection has an enormous impact on sheep production : 1 -Primary losses result from mortality. 2 - Reduced production during protracted convalescence including ( poor wool growth, and reduced reproductive performance including temporary ram infertility ).

Diagnosis • • case history. Clinical signs. Post mortem change. Laboratory diagnosis by using PCR.

Post mortem Multifocal haemorrhages with oedema visible on the cut surface of the submandibular lymph node

Post mortem wrinkling of the cornea reflects

Post mortem Extensive ecchymotic subepicardial haemorrhages

Diagnosis • Differential diagnosis from : • Foot and mouth disease. • Orf may cause ulcertaions on the mucous membranes but is not usually a cause of high fever or mortality. • Clostridial disease may cause sudden death and fever/oedema but this is usually sporadic and in unvaccinated sheep.

Treatment • Symptomatic treatment and care includes: NSAID to reduce pain, • fluid therapy to treat or prevent dehydration, provision of shade against the sun, • protection against extremes of temperature, use of mild disinfectants to irrigate affected areas, • general nursing care, the provision of a trough of cool water

Control and prevention • Bluetongue is a notifiable disease and, where suspected cases must be reported immediately to the Divisional Veterinary Manager at the local Animal Health Office. • Control of bluetongue is very difficult because of : 1 - The large number of potential hosts. 2 -virus serotypes. • Control is aimed to keeping susceptible animals away from the vector, this is not always practical. • Control of the midges can be attempted with pouron insecticides.

Control and prevention • Confirmation of suspected cases by laboratory tests. • Restriction of movement of animals if BTV is suspected may help with reducing spread to disease to free region. • Zoning to define infected and disease-free areas. • Vaccination of susceptible animals. • Surveillance to determine the extent of virus and vector distribution • Vector surveillance and control strategies.

Vaccination • The main prevention for BTV is vacciation. • The BTV-8 vaccines available in the UK are killed vaccines. • It is important to realize that here is no cross-protection between serotypes. • vaccination against BTV-8 will not protect against other serotypes of BTV. • The vaccines also do not act immediately with cattle requiring two doses of vaccine (and at least 6 weeks time from the first vaccination) to be protected. • Importing unlicensed vaccines is not advised as there have been several outbreaks of disease due to the use of live virus vaccines imported illegally from South Africa into Northern Europe, these may also not be the correct serotype.