Arboviruses

Arboviruses

1. Reoviridae

   • Tough in environment.
   • Orbiviruses
     • Replicate in LN and then to blood. They like the endothelial cells which causes vascular permeability, occlusion and oedema. Many serotypes each (makes vaccination hard).
     • Blue tongue
       • Culicoides midge in AUS. Confined to North AUS. Could come to NZ by importing ruminants into zoos
       • Signs=Swollen mouth, droopy ears, coronary band swelling, lameness.
     • African Horse Sickness
       • Highly fatal disease of horses and mules. Serotypes 1-8 (out of 9) are pathogenic.
       • Control=Vaccination (poly or monovalent), vector control, killing infected horses,.
   • Rotaviruses
     • Common cause of diarrhoea in infants - Disease seen in young animals 1-8 weeks old. Acid stable virus, hardy in environment. Factors contributing=chilling, overcrowding, poor hygiene, no colostrum. Diagnose with agglutination test. Control with vaccine.

2. Bunyaviridae

   • Can cause disease in humans. Can be transmitted via arthropod eggs too.
   • Rift valley fever
     • Not a huge threat to coming into NZ
     • Culex and aedes mosquitos
   • Akabane
     • Exotic to NZ- we don't have Culicoides
     • Causes reproductive issues in when it switched to epizootic cycle, no clinical signs in enzootic cycle.
   • Nairobi sheep disease
     • Not in NZ
     • Causes fever, haemorrhagic enteritis, abortion and mortality.
     • Diagnose by virus isolation, control by vaccine or tick control

3. Togaviridae

   • Alphaviruses
     • Fragile RNA virus
     • Encephalitis
       • Primary and secondary viraemia occurs, primary in LN and secondary in organs. It is infective to the arthropod at the level of secondary viraemia, and it then invades the CNS. Depression, incoordination, droopy face, impaired vision, circling, paralysis. You can vaccinate (also works to control human infection)
       • Eastern equine encephalitis
       • Western equine encephalitis
       • Venezuelan equine encephalitis
         • Abortion in humans

4. Flaviviridae

   • Easy to kill, Nucleic acid itself is infectious.
   • Dengue
     • Immunity for life for a single serotype only (no cross protection)
   • West Nile Virus
     • Uses humans and some mammals as secondary hosts
   • Of Veterinary Importance
     • Louping ill
       • Exotic to NZ Neurological signs. Control by vaccines and acaricides
     • Wellesbron disease
     • Japanese Encephalitis
       • Exotic to NZ Pigs are amplifier host (can get sick too though). Vaccine available.
   • BVD and MD
     • Outcome dependent on age, immunity, dose, strain and pregnancy status
     • BVD: Clinical infection is common in animals 6-18 months old, fever diarrhoea etc. High morbidity, low mortality.
       • If pregnant: Under 40days=Failure to conceive, 40-120 days=Persistently infected calf, 120-150 days=congenital defects.
         • Can vaccinate to control more persistently infected animals being born.
     • MD: Low morbidity, high mortality. Acute=Fever, erosions etc leading to death. Chronic=Erosions on muzzle, death in 2-6 months.
       • The BVD strain is either inherited or becomes cytopathic in persistently infected animals. They then shed the disease.
     • Diagnosis is by normal means, but PI animals are not antibody positive.
       • Prevention by vaccination.
   • Classical swine fever
     • Exotic to NZ Haemorrhage, ulcers, petechiae.

5. Equine infectious Anaemia

   • Of the lentivirus family but is an arbovirus too.
     • 1-3 week incubation followed by either acute or subacute forms of disease. Acute has serious effects followed by 80% mortality. Subacute has lifelong infection and shedding with recurrent episodes.
   • Exotic to NZ