RAJIV GANDHI COLLEGE OF VETERINARY AND ANIMAL SCIENCES

VETERINARY LABORATORY DIAGNOSIS

VLD – 421

ASSIGNMENT

TOPIC : BLUE TONGUE VIRUS (BTV)

SUBMITTED BY,

SENTHILNATHAN M

2010 – RU – 38

4th YEAR B.V.S.c & A.H.

BLUE TONGUE / SORE BLUE TONGUE / SORE MUZZLE / CATARRHAL FEVERMUZZLE / CATARRHAL FEVER

BLUE TONGUE VIRUS

ORBIVIRUS:• The virus particles of this genus have, double protein shell (i) outer being skin liked (ii) inner has 32 ring shaped capsomers icosahedral symmetry

• The virus consists of 10 segments of ds RNA

BLUE TONGUE VIRUS (BTV)• Insect borne infection and non-contagious diseases of domestic and wild ruminants

• Primarily a disease of sheep but cases of inapparent infection in cattle and goats take place and these may act as reservoir of virus

• The disease was recognized in Africa (1652)

• Virus was isolated and identified as serotype 3, 4, 9, 16 & 17 (Himachal pradesh), serotype 1, 4 (Haryana) & serotype 9 &18 (Maharashtra)

Properties: • Virus particle is spherical & about 69 nm in diameter with 32 capsomers• The capsid is double layered• The genome is of 10 segments ds RNA• The capsid contains four major and three minor polypeptides• Virus particle is resistant to ether, chloroform, deoxycholate, 4°C & -70°C• Inactivated below pH 6 and losses infectivity at -20°C• No haemagglutinin• There are 22 serotypes in BTV as revealed by VNT• Group specific antigens are revealed by CFT, AGID and IFT.

Cultivation :

• Grows in fertile eggs after inoculation of embryos 10 – 11 days old by I/V (OR) 6 – 8 days old embryos by yolk sac route• The I/V route is more sensitive• The embryos die by both routes of inoculation with multiple haemorrhages and are cherry red in colour• The optimum temperature of incubation of CE is 33.5°C• Virus can also be cultivated in 1-4 days old mice by intracerebral route of inoculation• After one or more passages in CE the virus grows in cell cultures like BHK21, Vero and L cells with production CPE • Lamb kidney monolayer cultures are less readily infected and the CPE production is less extensive

Epidemiology: • The BT disease is an African disease but now it has been reported from almost all the countries of the world• BTV has a wide range of host including sheep, cattle, goats, deer, African antelopes and various other Artiodactyles• The disease may be fatal and inapparent• Mostly the inapparent infection exists in most species• The infection progresses in cattle midge cycle and once certain level of infection is attained the infection spills over to sheep• Sheep are apparently involved in a secondary cycle

• Midges of the genus culicoides act as Biological vectors for BTV

• Midges become infected after feeding an infected animal and virus replicates in the salivary glands where it reaches a maximum titre in 6-8 days• The infected midge is infective for life• Transovarial transmission doesn’t take place in midges• Atleast 22 species of culicoides can transmit the disease• The transmission occurs only when infective midges bite the susceptible host are infective blood or tissue suspension are inoculated parenterly• The semen from infected bull during viraemic stage may be infective and cows inseminated with such semen become infected

Pathogenesis:• After infection the virus replicates in RLN and thereafter in other lymph nodes and lymphoreticular tissues and in endothelium, periendothelial cells and pericytes of small blood vessels• This leads to the degenerative changes and necrosis leading to vascular occulusion, stasis and exudation.• Once replication in target cell take place, the virus appears in the blood stream and spreads to entire body• Virus is detected in blood from about 3-6 days PI and viraemia reaches its peak in about 7-8 days and then declines rapidly

• After 14 days the virus is not detected in the blood of sheep but in cattle viraemia persists for a longer period• The virus is cell associated involving blood cells• A panleucopenia proceeds the appearance of viraemia• In cattle there is evidence that expression of clinical disease is due to IgE-mediated hypersensitivity reaction induced by previous exposure of BTV or related viruses, however, it doesn’t happen in sheep• In sheep the incubation period is 6-7 days• The virus causes viraemia and is easily isolated from during the febrile stage

• The affected sheep have a marked fever, oedema of muzzle, oedema and hyperaemia of the lips, buccal, nasal mucosa of eyelids• There is nasal discharge which may become mucopurulent• The saliva drops from the lips and muzzle becomes encrusted with discharge from the nose and mouth• There is swelling and hyperaemia of the mucosa of mouth and ulceration of tongue, dental pad and lips.• The tongue become swollen, cynotic and purple blue• Swelling and tenderness of coronary band and sensitive lamina of hoof results in lameness• Pregnant ewes may abort• Mortality in sheep may be high

SORE MUZZLE BLUE TONGUE

THICKENING OF

THE TONGUE

DEFLEECING OF WOOL

• Experimental diseases in cattle is subclinical

• In natural infection, laminitis, stiffness, ulcers in the mouth, nose and muzzle and salivation are seen

• In affected pregnant cows the foetus may die and be reabsorbed, aborted or stillborn

• The BTV has teratogenic properties

• Affected newborn lambs or calves are blind ataxic, undersized and have congenital defects

Immune reaction:• In immunocompetent animals the group specific and type specific antibodies appear within 7-10 days of infection• The type specific neutralizing antibodies persist for more than 3 years, while the group specific antibodies persists for only 6-18 months• The protective immunity is generally associated with neutralizing antibodies but sometimes animal resist infection of BTV with no demonstrable neutralizing antibodies• The CMI responses to BTV infection in sheep are also protective and may be less type specific• Lambs born to BTV immune animals are passively immune and remain protected upto 6 months

Diagnosis:• Clinical signs• Viral isolation from blood, spleen, lymph nodes and in chicken embryos• The blood should be collected from febrile animals in the early stages in EDTA or citrate• Occasionaly isolations can also be made by intracerebral inoculation of newborn mice or inoculation of cell cultures, BHK21, Vero or Aedes albopictus cells• The embryos die within 6 days of inoculation with haemorrhages• Infected CAM is used as a source of virus in VNT, CFT, ELISA, etc.

Control:• Live egg adapted polyvalent vaccines are effective

• The live vaccines are not recommended to be used because the live virus may cause some abnormalities in foetus

• Promising results are being obtained with inactivated vaccines

• Import controls is practised in certain countries like Australia

Thank you