bluetongue. background to the disease current situation in the uk clinical signs in sheep and cattle...
TRANSCRIPT
Bluetongue
Background to the disease
Current situation in the UK
Clinical signs in sheep and cattle
Methods of control
A VIRAL DISEASE24 serotypes
Affects ruminants and camelids
DOES NOT AFFECT MAN or other animals
No effective treatment
A VECTOR-BORNE DISEASE
Not contagious – indirect transmission
Increase in vector borne diseases worldwide since 1970s
Vector borne diseases
UKBabesia sp - Babesiasis - ticksRickettsia - Tick borne fever - ticksLouping ill virus - ticksBluetongue virus – culicoides midge
WorldErlichiosis (heartwater) – Sub-saharan AfricaTrypanosomiasis – Sub-saharan AfricaTheileriosis – Middle EastAnaplasmosis – Southern Europe
Transmission
Midge bites viraemic animal (2% infection rate)
Virus passes through the gut wall of the midge and replicates in midge salivary glands
Midge bites naive animal and injects saliva (100% infection rate)
Virus replicates in animal cellsAnimal becomes viraemic
Transmission
Cattle viraemic for 50-60 daysSheep viraemic for 10-20 days
So how does the virus survive over-winter in northern latitudes when the
midge is inactive?
Virus multiplies in midge more quickly in hot weather Will not multiply when temp < 150C
Possible multiple mechanisms
In adult midges
In midge larvae
In adult animals
In animals passingfrom dam to foetus
Overwintering
Bluetongue virus is spreading
Trade - greater animal movements?Virus changing?
New vectors
Global warming
Bluetongue distribution before 1998
Bluetongue distribution in 2007
42
4
Spread within Europe - 2003
4
16
4
2
4
9 + 16
Spread within Europe - 2004
4
4 44
16
4
22
4
1
11 1
9 + 16
Spread within Europe - 2006
444
4
8
1624
How did BTV8 arrive in Northern Europe?
Imported carrier ruminants?
Infected midges?
Wind borne?On other animals?On plants?
How did BTV8 arrive in the UK?
Imported carrier ruminants?
Infected midges?
Wind borne
Wind Plume From Mainland Europe
Initial midge hatch starts here on the evening of the 4th August 2007
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
Wind Plume From Mainland Europe
The morning of the 5th August conditions change and midges drop out of the plume to land in Norfolk and Suffolk
4 August – winds blow infected midges from Netherlands to East Anglia
22 Sept – disease confirmed in Ipswich
30 Nov - 65 premises confirmed
23 more premises in Jan and Feb 08 detected through pre-movement testing
Situation in UK
22nd February
29th February
No more pre-movement testing after March 15th
Zones fixed until next outbreak
Clinical Signs
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Short lived fever – dull, off food, reluctant to rise
Vascular disease – attacks blood vessels
Oedema - swollen face, ears, legs
Salivation – ulceration of the mouth and nose, drooling
Redness of gums, eyes, coronary bands of feet
Respiratory distress – difficulty breathing
Weight loss, wool slip
Clinical Signs
Ulceration of tongue
Ulceration of lips and dental pad
Locomotion
• Isolated from the flock
• Unwilling to stand
• Stiff or lame – hunched appearance
• Coronitis, laminitis, arthritis
• Loss of condition (inability to move / eat)
Morbidity 27%Mortality 11%
Recovered animals
Loss of body condition – 6 weeks to recover
Milk yield drop
Poor lamb growth, wool slip
Infertility
Ewe: Abortion (5-6%),
Embryonic deaths = lower lambing
Ram: Poor sperm quality, low pregnancy rate
May be sterile for up to 1 year
Clinical Signs in Cattle
• Wide Variation in Clinical Signs• Low morbidity (+/-10%) in affected herds with only one or two
animals showing clear clinical signs.
• Low mortality (2%)
• Initial signs:
• -Slow, stiff gate, depressed
• -Decrease in appetite
• -Drop in milk
• -Reddening of the whites of the eyes, inside of the nose and nasal discharge
The Following Days
• Erosions of the muzzle
• Sunburn-like lesions on the white skin of the nose and teats
• Purulent nasal discharge, frothy drool
• Erosive lesions on roof and bottom of the mouth
• Sub endothelial haemorrhages
• Swollen feet, inflammation of the coronary band
• Oedema of the lower limb
Supportive therapy
Warmth and shelter
Antibiotics, fluids and anti-inflammatories
Diet
Treatment
Low morbidity – only 2-3 cases per farmBlood test – 16% cattle +ve
- 5% sheep +ve
BUT
Experience on continent is that in the 2nd year there are more cases and greater severity
The same farms are often re-infected.
Experience in UK to date
Reduce/eliminate vectors
Prevent sheep and vectors interacting
Restrict animal movements
Vaccination
Control
Control the vector
Total elimination of midges impossible
Reduce numbers
Reduce stagnant water
Larvicidal treatments
Insecticides
Insecticidal sprays
Sheep dips
Don’t move animals at dawn and dusk
Don’t stop vehicles overnight
Darken the inside of vehicles
Prevent midge biting sheep
Restrict animal movements
Modified live vaccines – banned in EU
Inactivated vaccines – permitted in EU
24 immunologically distinct serotypes
No cross-protection between serotypes
Many strains within serotypes
Vaccination
Vaccination
BTV 8
Intervet - virus from 2006 infected cow
Killed vaccine
Single dose for sheep, double dose for cattle
1ml dose in 20 and 50 ml bottles
Annual booster
Vaccination
Compulsory?
Voluntary?
Need high take up for control – 80%
Vaccination
2 million doses due for release in May 2008
For use in the PZ areas only
Purchased through vet, but can be administered by farmer
Vet certification needed for export
Record all use in medicine books
Questions?