BLUE
TONGUE
Bluetongue is an insect-borne,
non-contagious, viral disease primarily of sheep and other ruminants characterized by microvascular
thrombosis associated erosions, ulcerations, hemorrhages, edema and
necrosis on the mucous membranes,
visceral organs, muscles and the
coronary band
Introduction
It is infectious non-contagious arthropod
borne virus disease of domestic and wild animals.
The name Blue tongue owes its origin from the
Dutch word “Blaau tong” means Mouth sickness.
Synonyms
Catarrhal fever,
Sore mouth,
Sore muzzle,
Pseudo foot and mouth disease,
Stiff lamb disease.
Etiology
Family – Reoviridae
Genus – Orbivirus
Species – Blue tongue virus (RNA Virus)
Twenty
six antigenic strains of the virus have been
identified, which very in their pathogenicity of which 18 from India.
Susceptible Hosts
It is predominantly a disease of sheep but occasionally
cattle and goats are affected.
Young sheep (up to one year) more prone to
infection.
Suckling lambs are relatively resistant due to
passive immunity acquired through colostrum.
White tail deer and other ruminants may
naturally infected.
Mode of transmission
It is infectious non-contagious arthropod
borne virus disease.
It is spread through blood sucking midges of
genus culicoides or mosquitoes or other ectoparasites like
sheep ked & Melophagus ovinus.
White
tail deer and antelope
are consider as reservoir of infection and thus act as a carrier.
Transmission through semen and placental route is possible (Vertical transmission).
Major route of infection
Biting midges or
gnats
Genus Culicoides
Minor
importance route of infection
Ticks
as can be mechanical vectors
Mechanically on surgical equipment and
needles
BTV can be found in semen and venereal
transmission from bulls is possible
Pathogenesis
Culicoides take virus infected blood meals
⇓
Virus replication in Culicoides
⇓
Infect salivary glands (15 days)
⇓
Introduce BTV virus in
other animals by biting
⇓
Virus enter in to the
skin and S/C tissue
⇓
Infect/taken by APC cells
(antigen presenting cells)
⇓
Taken to the regional
lymph nodes
⇓
Virus multiplication in
nodes
⇓
Infect other lymphocytes, monocytes, macrophages
⇓
Infected cells enter in to blood circulation via thoracic ducts
⇓
Disseminated to all
visceral organs via blood
⇓
Infected cells adhered to
endothelial cells (EC)
⇓
Virus induced lysis of infected cells and enter in to the EC
⇓
Virus replication in EC
⇓
Necrosis and lysis of EC
⇓
Vasculitis and thrombus
formation in organs and mucosa
⇓
Ischemic necrosis
(infract, ulcers), edema and hemorrhages, DIC (Disseminated intravascular
coagulation)
⇓
Death
Clinical signs
Morbidity
– 50%
Mortality
– 10 - 90%
Incubation period – 1 to 10 days.
The
disease has been divided into three form –
1.
Acute form -
High
rise of temperature
Nasal
discharge
Salivation
Lacrimation
Swelling
of tongue, gum and lips.
Ulceration
and extensive necrosis of lip, dental pad, gum and tongue.
Cyanotic
and bluish appearance of tongue.
Udder
may be swollen and teat may show signs of ulceration.
Coronary
band may become swollen and it may crack.
Hoof
may become may separate leading to lameness.
Exposure
to sun rays seems to increase the severity of the infection. (So disease more
prevalent in late summer and early autumn).
Torticollis
Pneumonia
Dyspnea
and snoring.
Diarrhea
Loss
of appetite.
Reduction
in body weight.
2.
Sub-acute form or Sub clinical form in cattle.
3.
Abortive form (characterized by abortion)
Sheep
Fever, Excessive salivation
Leukopenia
Oral hyperemia, edema, erosions and
ulcerations
Tongue - Swollen, protruding, cyanotic “blue-tongue”
Serous nasal, ocular discharge becomes mucopurulent
Depression, Dyspnea and panting
Coronitis and Lameness
Abortion or congenital defects
Cattle
Usually
asymptomatic
Erosions,
crusts around nose and teats
Coronitis,
Reproductive failure
Macroscopic
Pathology
Face and ears
edematous
Edema and hemorrhages
in internal organs and oral cavity
Coronitis, loss of
hooves
Subcutaneous and
intermuscular blood tinge edema
Superficial lymph
nodes - enlarged and edematous
Lung - edema and
hemorrhages
Widespread
myo-degeneration and necrosis
Widespread petechial
to ecchymotic hemorrhages
Hemorrhage at the
base of the pulmonary artery
Progeny- Congenital
defects, hydranencephaly, Arthrogryposis
Microscopic
Pathology
Microvascular thrombosis, and edema and hemorrhage in affected sites
recognized at necropsy.
Ulcers and acute inflammation at various site like skin and mucus
membrane
Muscle – hemorrhages, edema, necrosis
Diagnosis
Based
on history and clinical findings
Animal
inoculation test
Isolation
of virus
Complement
fixation test
Agar
gel immuno diffusion test
ELISA
Differential diagnosis
Foot
and mouth disease
Malignant
catarrhal fever
Photosensitization
Treatment
There
is no specific treatment
Only
symptomatic treatment should be done.
Localized
lesions may be treated with topical antiseptic solution to accelerate rate of
healing.
Antibiotic
also given for secondary bacterial infection.
Affected
animal should be kept away from direct solar exposure.
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