64. Bluetongue.

Question 1

Bluetongue virus family and info?

Answer 1

Reoviridae family

Reoviridae (Respiratory enteric orphan)

• Seroreovirinae subfamily (without projections ‘still surface’)

• 6 genera, 36 species: viruses of mammals, invertebrates, plants, protozoa
• Genera and species with veterinary impact

‣ Orbivirus genus

๏ African horse sickness virus

๏ Equine encephalosis virus

๏ Bluetongue virus

‣ Rotavirus genus

๏ Rotavirus A-J

๏ Seadornavirus genus: human, flu-like symptoms, arbovirus

• Spinareovirinae subfamily (with surface projections) ➝ haemagglutination

• 9 genera, 58 species: viruses of mammals, birds, invertebrates, plants, fungi
• Genera and species with veterinary impact

‣ Orthoreovirus genus

๏ Avian orthoreovirus

๏ Mammalian orthoreovirus

‣ Coltivirus genus: transmitted by ticks e.g. Colorado tick fever virus

‣ Aquareovirus genus: fish, orphan or haemorrhagic disease e.g. in grass carp

Question 2

Morphology and resistance?

Answer 2

• Morphology

• dsRNA, linear, segmented: 10-12 segments
• Icosahedral, double layered capsid (80-82 nm)
• Non-enveloped

• Resistance: diverse

• Orbivirus: pH 5, sensitive in the environment (1-2 days) ➝ arboviruses
• Orthoreovirus: pH 2-9, maximum 55℃, resistant even in extreme ionic environment
• Rotavirus: pH 3-9, maximum 50℃, resistant in the environment (4-20℃ month

Question 3

Biological properties?

Answer 3

Biological properties

• Biological properties

• Segment reassortment ➝ genetic diversity
• Isolation: orthoreoviruses easier, orbi- and rotaviruses more complicated
• Relatively euryxen viruses
• Orbiviruses - arboviruses: mosquitoes, midges biological vectors
• Orthoreoviruses, Rotavirus ➝ haemagglutination
• Antigenicity

‣ Common surface antigens ➝ serological cross-reactions (CF test)

‣ Protective antigen (VN) might be serotypes-specific ➝ vaccines (Bluetongue: 29 serotypes)

Question 4

History, Occurrence?

Answer 4

Bluetongue

Viral disease transmitted by insect vectors, with endothel damage, oedemas, haemorrhage, mucosal erosions, lameness and foetal

developmental disorders in sheep and cattle.

History, Occurrence ➝ Notifiable disease

• African origin: worldwide distribution ➝ mainly in warmer regions
• Before 1998: Africa, Asia, Australia, USA, South America, occasional introduction in Europe
• After 1998: reaching the Mediterranean countries of Europe from different directions, slow spread towards North
• Vector: Culicoides imicola presence ➝ global warming
• Different serotypes: mainly serotype 1, 2, 4, 9 and 16

• The emergence of serotype 8 in Western Europe in 2006

• Most likely from Africa, rapid geographic spread in Western Europe in 2006
• Hungary since 2007
• Pathogen for sheep, goats and cattle too

Question 5

Causative agent?

Answer 5

Causative agent:

Bluetongue virus (BTV)

• 29 serotypes known so far

• Common surface antigen (CF, AGID, ELISA)
• Protection is serotype-specific

• Vectors: midges/gnats (ticks too)

• Culicoides
• In vitro virus cultivation in embryonate eggs
• Biological sector without transovarial transmission

• Hosts and susceptibility

• Sheep ➝ African local breeds are usually more resistant
• Cattle ➝ certain serotypes are highly pathogenic in them
• Goat ➝ more resistant
• Other domestic and wild ruminants ➝ can be susceptible (reservoirs)

Question 6

Epidemiology?

Answer 6

Epidemiology

• Seasonal occurrence - vector activity
• Mainly in summer, autumn (not exclusively)
• Long-distance spread
• Vectors transported by the wind ➝ 50-250 km
• Transport of infected ruminants
• Sheep carry for about 2 months
• Cattle are asymptomatic carriers for years
• Can be transmitted by semen too
• Transplacental infection can lead to immunotolerance

Question 7

Pathogenesis?

Answer 7

Pathogenesis

1. Midge bite
2. Primary multiplication in the lymphatic tissue
3. Viraemia in 5-11 days
4. Endothelial damage
5. Oedema, haemorrhages

• Mucosal surface, skin, muscle damage too
• Transplacental infection ➝ abortion or developmental problems
• Hydrocephalus
• Cerebellar hypoplasia
• Jaw developmental disorder

Question 8

Clinical signs?

Answer 8

Clinical signs

• Usually after 3-7 days incubation
• Variable severity depends on strain virulence, host species, breed
• Sheep
• Fever (41.5℃ for 4-12 days), depression, dyspnoea
• Oral, nasal mucosa hyperaemia, serous nasal discharge (within 1 day)
• Conjunctivitis, eyelid oedema, lacrimation
• Oedema under skin - head, ears, chin, neck
• Swollen, protruding, cyanotic tongue
• Erosions on the muzzle and oral mucosa (on days 2-3)
• Ulcers covered with greyish, necrotic membrane ➝ putrescent discharge on days 4-7
• Oedemas, erosion on hooves, at the coronary band, laminitis
• Muscle damage ➝ movement problems, torticollis
• Enteritis in lambs ➝ even haemorrhagic
• Death within 1 week (10%) or recovery
• Loss of wool, weight loss
• Abortion, congenital defects

• Cattle

• Frequent subclinical infection
• Nasal discharge, reduced milk production
• Lip, eyelid oedema
• Nose, mouth, muzzle erosions, ulceration, pseudomembranes
• Congenital defects ➝ abortion, hydrocephalus, deformed legs and feet

• Goats ➝ usually subclinical carriers

Question 9

Diagnosis?

Answer 9

Diagnosis

• Seasonality, signs, pathology ➝ suspicion
• Notifiable disease ➝ laboratory diagnosis is necessary (virus identification)
• RT-PCR, virus isolation (rarely, in embryonated eggs)
• Serology: ELISA, CF, AGID (VN)

Question 10

Differential diagnosis?

Answer 10

Differential diagnosis

• FMD ➝ vesicles
• Sheep pox ➝ nodules, less oedema and haemorrhage
• Contagious echythema ➝ lesions mainly on lips, no oedema and haemorrhage
• IBR ➝ upper respiratory tract inflammation, coughing, less oedema
• BVD-MD ➝ sporadic, sharp edged erosions
• Malignant catarrhal fever ➝ eye lesions, CNS signs, sporadic
• Panaritium ➝ no mouth lesions
• Vitamin E and Selenium deficiency ➝ mainly muscular problems

Question 11

Prevention & Control ?

Answer 11

Prevention and Control- Notifiable

• Notifiable disease ➝ legal measures for the control

• Restrictions

‣ Restricted zone: 20 km

‣ Protection zone: 100 km

‣ Surveillance zone: 150 km

• Slaughter of affected animals, vector control, monitoring
• Prevention of introduction, quarantine
• Separation of seropositive pregnant animals, virological testing of newborns
• Emergency vaccination ➝ with inactivated vaccine

• In endemic countries: attenuated vaccines

• Africa ➝ polyvalent attenuated vaccine
• Other countries ➝ serotype-specific, monovalent vaccines
• They can be foetopathogen
• Shedding of the vaccine strain, infection of vectors, risk of reversion

Question 12

Pathology, Histopathology?

Answer 12

Pathology, Histopathology

• Haemorrhages in the airways, oral cavity and rumen
• Cyanosis, oedema, erosion on the mucosa
• Lambs ➝ haemorrhagic gastroenteritis
• Myocardial and muscle dystrophy
• Cerebellar hypoplasia in aborted foetuses and in newborns
• Histopathology: endothelial necrosis, inflammation and thrombosis