BLUETONGUE in Angora Goats?

Tuesday, 18th October 2016

 BLUETONGUE in Angora Goats?

Bluetongue is well known by sheep farmers in the Karoo. The effects of the disease on Angora goats are less well known. Angora goats have been shown to be susceptible to experimental infections with bluetongue virus but apart from a fever reaction showed no clinical signs.

Angora goats are susceptible to natural disease but certainly have higher resistance than sheep. With a large number of bluetongue strains and the variable pathogenicity, these may account for ill-defined syndromes characterised by various symptoms including fever, anaemia, stiffness and even hair loss where bluetongue antibodies were demonstrated?

The virus in experiments has been demonstrated to remain in the blood of Angora goats for up to 20 days infection so they potentially could act as a source of infection for sheep (amplifying host).

Must I vaccinate?

Vaccinating Angora goats against Bluetongue is unusual and not something Mohair producers do due to the goat’s natural resistance. The disease in Angora goats, however, needs to be monitored as vaccinating could be considered in future if clinical signs become more prominent or to reduce the ‘reservoir’ population.

 

How is BT transmitted?

The BT virus is transmitted by Culicoides (midges). Bloodsucking flies can potentially also be vectors. The virus replicates in the salivary glands and is transmitted when the midge bites. Animal tissues and secretions cannot transmit the virus (one exception is semen from vireamic bulls). Trans-ovarian transmission of the virus in culicoides does apparently not occur so reservoirs for the virus are required (ruminants such as cattle and wildlife)

Outbreaks usually occur in late summer or Autumn.

Serotypes and their occurrence.

Over a period of 6 years, 14-18 isolates have been found. Usually, 3-5 serotypes dominate in a season and these are largely replaced by others the next season and become dominant again 3-4 years later. Types 1-6,8,11,24 have a high epidemic potential due to this cycle. Types 9.10.12, 13, 16, 19 occur every year.

The other types 7, 15 and 18 appear sporadically and have lowest epidemic potential. See the paragraph on Vaccination.

 

Clinical signs in sheep:

BT affects a wide range of animals (most ruminants) but sheep are most at risk. Signs vary between species and even breeds of sheep from clinical signs that are not apparent to a mortality rate of 2-30%. Signs can be confused with photosensitivity by plant poisoning and some post-mortem findings can resemble Heartwater and pulpy kidney.

The incubation period is about 7 days. Peracute cases die within 7-9 days. Mild cases usually recover rapidly.

  • Rise in temperature (peak 41-42C) and lasts 6-8 days.
  • Hyperaemia off buccal and nasal mucosa and on more exposed parts of the muzzle and around eyes and on ears.
  • Increased salivation, tear production and nasal discharge
  • Often licking movements by tongue and smacking of lips
  • Swelling of the tongue, lips, face, eyelids and ears 2 days after the start of the fever.
  • Mandibular oedema may extend down the neck

Mild cases can recover but severe cases progress to develop:

  • Erosions on muzzle, nostrils and in mouth
  • Severe swelling of the tongue which may become cyanotic
  • Progressive weakness, rumen stasis and occasionally haemorrhagic diarrhoea before death
  • Watery nasal discharge becomes mucopurulent and forms crusts
  • Lung oedema occurs in per-acute cases where dyspnoea, frothing at mouth and nostrils occurs.
  • Foot lesions develop at the end of the febrile reaction. Hyperaemia of the coronary bands becoming streaky in the appearance later. The sheep appear lame
  • Degeneration and necrosis of skeletal muscles in the neck may lead to torticollis.
  • Hyperaemia of the skin is most severe in those areas exposed to sunlight
  • A break in the wool may cause the fleece to be shed 3-6 weeks later

 

Immunity and Vaccination

Sheep infected by homologous serotype develop lifelong immunity but only partial or no immunity to heterologous types.

Strains 15,16,18,22,23,24 are not in the vaccine as low pathogenicity.

After 2-3 annual vaccinations, most sheep are immune to all serotypes

The BT vaccine is a live attenuated virus. The serotypes are contained in 3 bottles A, B, C. The vaccines are injected in the order A (type 1, 4,6,12, 14) B (Types 3, 8,9,10 and 11) C (types 2, 5, 7,13and 19) 3 weeks apart. 1ml subcutaneously under the skin. A fever reaction may occur after 7 days post vaccination.

Store the vaccine in a refrigerator at 4 ËšC to 8 ËšC. Do not use after the expiry date printed on the bottle.

Vaccinate sheep from August to October. Immunisation of ewes should commence 9–12 weeks before mating. It is not advisable to inject pregnant ewes during the first half of pregnancy. Rams should be inoculated after the mating season. Inject lambs from immunised ewes at the age of six months and older. If done at an earlier age in heavily infected areas, lambs must be revaccinated at the age of six months. Sheep must be vaccinated annually.

The older vaccines did not work effectively as all the stains were in one vaccine and hence why it is not advisable to mix the A, B, C.

The cold chain is critical as it is an attenuated live vaccine. Keep at 4-8C.

Control

Because reservoirs for the virus (Angora goats, cattle, wildlife) exist eradication of the disease is impossible.

  • Protect sheep from contact
  • Avoid low-lying wet areas
  • Allowing wool growth in late summer autumn
  • Use of insect repellents on the bare skin of sheep during an outbreak
  • Midges prefer cattle
  • Place valuable animals in a shed during the late afternoon, at night and early morning.

 

Treatment

Supportive care;

  • Shade, water
  • Soft food
  • Anti-inflammatory drugs to reduce pain, inflammation (Home treatment with aspirin 10mg/kg can be dosed)
  • Sheep can be stomach tubed with electrolyte mixtures

 

Post Mortem findings.

  • Ulceration of lips, dental pad, cheeks and tongue.
  • Hyperaemia and ulceration of forestomach
  • Small local areas of hyperaemia to large haemorrhagic lesions can occur in intestine
  • Hyperaemia, oedema of mucosa of nasal cavity, pharynx and trachea
  • Hyperaemia and oedema of lungs
  • Froth in trachea and hydrothorax with occasional aspiration pneumonia
  • Haemorrhages in the tunica media of the pulmonary artery
  • Epi and endocardial haemorrhages
  • Fluid in pericardial sac may also occur
  • Degeneration of muscle in the neck with oedema and haemorrhage.

Diagnosis

  • Clinical signs and PM findings
  • Serology and virus isolation on blood samples

  

 

 

REFERENCE:

Infectious diseases of livestock. Coetzer, Thoson, Tustin

Considerations with regard to Bluetongue vaccination of Angora goats. EM van Tonder

Baltus Erasmus .Deltamune (Pty) Ltd. Lyttelton, Pretoria.(Former Head : Onderstepoort Biological Products)

 

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