Flaviviridae, Togaviridae, Reoviridae Flashcards
Flaviviridae
- positive sense ssRNA
- enveloped; labile in environment
- vectors (arthropods) important in transmission
Flaviviridae is separated in 2 generas
- Flavivirus
2. Pestivirus
Significant Flavivirus
- Japanese encephalitis (JE) virus
- Louping ill virus
- West Nile Virus (WNV
- Kunjin Virus (KUN)
Epidemiology of Flavivirus
- Arboviruses; transmitted by arthropods- infects a range of vertebrate species, mammals, bird
Pathogenesis of flavivirus
- Arthropod bites
- replicates in LN at site of inoculation
- virameia
- Dissemination (other organs, tissues, and brain)
- replication–> disease
Enveloped viruses need what responses?
Humoral AND cell mediated responses
Flavivirus immunity
- Neutralises antibodies to envelop proteins; recovery and long term immunity
- non-structural viral proteins induce cytotoxic T cell response
Japanese encephalitis (JE)
- most important mosqito-borne pathogen
- mosquito-pig-mosuito transmission cycle
Main reservoir host of JE
Waterfowl- also amplifying host
Pigs are also important amplifying host
JE in humans and horses
- severe and fatal encephalitis
- dead end (horses and humans cant infect mosquito)
JE control
- horses must be vaccinated prior to travelling to aus
- ectoparasite control
West Nile virus
- human, horse and birds
- lethargy, depression, fever
- threat to AUS
- mosquito vector
West Nile Virus control
- reduce vector numbers; drain standing water to prevent breeding mosquitos
- reduce risk of exposure to vectors; reduce dawn dusk outdoor activities when mosquitoes are active- keep horse in stable at the time, insect repellant
- vaccination
Pestiviruses
- classic swine fever virus (hog cholera)
- Bovine Viral Diarrhea virus (BVDV)
Hog cholera
Pestivirus exotic to aus.
- oral/respiratory
- replication in tonsil–> viraemia00> haemorrhagic disease–> vomiting, diarrhoea, coughing, tremor
BVDV
2 syndromes:
- Bovine viral diarrhoea
- Mucosal disease
Pathogenesis of BVDV
- oral/nasal route
1. replication in oronasal mucosa
2; viraemia; immunosuppression, transplacental spread
3. attacks rapidly dividing enterocytes of intestinal crypts
4. diarrhoea and intestinal haemorrhage
Transmission BVDV
- contagious secretions
- mutations compromise herd immunity
- rare indirect spread bc environmentally labile
- no arthropod vectors
BVDV in non-pregnant cattle
- drop milk yield
- 2 degree bacterial infection
BVDV pregnant cow
- biggest problem
- transplacental spread to fetus
- fetal death <125 days
- > 125 days; develop neutralizing antibody, eliminates virus
Consequences of early pregnancy (80-125 days) transplacental transmission BVDV
- cow and fetus infected w non-cytopathic BVDV in early pregnancy
- cow becomes immune. Fetus becomes tolerant and unable to make antibody
- Calf remains infected w virus for life
- mutation of virus to cytopathic form may occur
- superinfection of this and other viremic animals w cytopathic virus causes fatal mucosal disease
BVDV diagnosis
- muscosal; chronic
- bovine viral diarrhea; acute
- detect virus using cell culture virus isolation; faeces, blood, immunohistochemistry, RT PCR
BVDV control
- killed vaccine- limited success
- live vaccines; may cause severe mucosal disease in persistenyl infected animal
- immunotolerant animals are biggest source of virus
- faecal screening for viral antigen or RNA of progeny
- eliminate positive
- biosecurity
- change clothing, disinfect
Togaviridae
+ssRNA, enveloped
Togaviridae genus Alphavirus
- Arboviruses
- picked up from blood meals from animals
- non-cytopathic in insect vector
- replication in salivary gland
- transmission by biting other animals
- mechanical biological vector
Significant togaviruses
- Eastern equine encephalitis (EEE)
- Western equine encephalitis (WEE)
- Venezuelan encephalitis (VEE0
- Ross river (RR)
- Getah virus
Basic pathogenesis of togavirus disease
- animal is bitten by infected insect
- virus enters bloodstream, taken up by mononuclear cell and viraemia occurs
- replication occurs in spleen and lymph nodes
- cell associated secondary virameina which results in clinical signs
- If sufficient, virus is produced during secondary phase to escape immune protection and to reach critical target tissues–> severe systemic disease and encephalitis
RR and Getah virus do not
produce encephalitis in horses
WEE and EE epidemioloy
Reservoir hosts: birds and small mammals (mortality and disease in these hosts)
vectors: mosquito
human horses: dead end
Epidemioogy of VEE
- in rainforests
- cycles between mosquitoes and forest rodents; reservoir hosts
- produces high viraemiea in horse- mosquito cycle
Signs of WEE and EE in horse
- fever, hypersensitivity, aimless walking, circling, death after 4 days
signs of VEE
- similar encephalitis signs of WEE and EEE
WEE EEE VEE diagnosis
- ELISA, haemaglutination, Viral isolation
WEE EEE VEE control
reduce insect vector conc; drain standing water, pesticide, clothing, repellent
Reoviridae
- dsRNA
- non-enveloped
Significant reoviruses
- Rotaviruses; cause enteritis and diarrhoea in all domestic animals
- stable over wide range of pH and survives month in faecal contaminated env and long periods in water
Diagnosis reoviruses
- Faecal/intestinal contents
- EM, direct ELISA, RT-PCR, difficult to culture
Treatment control Reoviruses
Treatment: supportive therapy, replace milk w water and electrolytes
control: reduce exposure to virus; young animals, clearning, disinfecting, vaccinate pregnant dams, ensure adequate colostrum, minimise stress
Bluetongue virue
An orbivirus mainly in sheep and other ruminants
Host factors: age and breed of sheep
Environmental factors: nutritional status and exposure to sunlight
Culicoids spp (midges)
- female midges infected when feeding on infected animal
- virus replicates in their tissues
- transmite via saliva and is infectious for life
- movement via environmental conditions; wind, seasonal, climate change
Pathogenesis of bluetongue
- replication in regional LN from site of inoculation and carried in blood to lymphocytes for further replication
- Localization and multiplies in endothelium of small blood vessels
- Viraemia
Clinical signs of blue tongue
- fever, depression, lameness, ulcers, oedemin in lips and tongue, fleece loss
Bluetonge diagnosis
- clinical findings, post mortem
- viral isolation LN, spleen
- RT PCR
- ELISA
Bluetonge control
- ectoparasite control
- killed vaccine
