- Blue tongue virus is an orbivirus that causes blue tongue disease, a non-contagious disease of domestic and wild ruminants spread by midges. It primarily affects sheep but can also infect cattle and goats. - The virus replicates in lymph nodes after infection and spreads through the bloodstream. In sheep, it causes fever, swelling of the lips and tongue (which become purple) and lameness. Mortality can be high in infected sheep. Cattle typically only show mild or subclinical symptoms. - The virus is transmitted between ruminants by bites from infected midges of the culicoides genus. Live attenuated and inactivated vaccines provide effective control of the disease.

1. 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.

2. BLUE TONGUE / SOREBLUE TONGUE / SORE
MUZZLE / CATARRHAL FEVERMUZZLE / CATARRHAL FEVER

3. 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

4. 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)

5. 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.

6. 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

7. 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

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

9. • 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

10. 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

11. • 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

12. • 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

13. SORE MUZZLE BLUE TONGUE

14. THICKENING
OF
THE
TONGUE

15. DEFLEECING
OF WOOL

16. • 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

17. 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

18. 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.

19. 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

20. Thank you