RNA Viruses and Prions

List the RNA viruses covered in lecture

• rabies virus: single stranded, helical, enveloped

• bunyavirus: single stranded, helical, enveloped

• flavivirus: single stranded, icosahedral, enveloped

• coronavirus: single stranded, helical, enveloped

Rabies virus properties

• single stranded RNA

• enveloped

• helical

• bullet-shaped morphology

Rabies virus replication site

cytoplasm

Rabies virus target organ

brain

Rabies is what % vaccine preventable?

100%

what system does rabies virus affect in mammals?

CNS

How is rabies transmitted?

saliva or aerosol of infected animals a few days before death when the animal sheds the virus

What is a pathogonmic finding indicating the presence of rabies encephalitis?

Negri bodies - intracytaplasmic inclusion bodies found in the neurons

Rabies virus becomes non-infectious when

dried out or exposed to sunlight

Rabies virus only affects what groups of animals?

mammals

Rabies susceptible hosts

• bats

• raccoons

• skunks

• foxes

• coyotes

• wolves

• dogs

• cats

• horses

• cattle

• goats

• ferrets

Rabies pathogenesis

• entry

• enter peripheral nerves

• brain and spinal cord

• spreads to other body parts

• saliva

Rabies virus clinical signs

• variable

• several months

Prodromal period of rabies

• confused

• lose natural fear of humans

Furious (excitation) stage of rabies

• aggressive

• hyperexcitability

• bite inanimate objects and other animals, roaming long distances

Dump (paralytic) stage of rabies

• muscle weakness

• difficulty swallowing

• profuse salivation

• hydrophobia

Rabies treatment

• no cure/treatment

• no premortem testing

• if suspected:

  • isolate animal

  • prevent escape

  • animal dies within 5 days of clinical sign development

Is rabies zoonotic?

YES

Human risk factors for rabies

• activities: exploring caves where bats live, camping

• working as veterinarian/veterinary tech

• working in a lab where rabies virus is present

Rabies bite management

• extensive wound washing: soap and water/povidone iodine → kills virus

• multiple rabies shots

Rabies prevention

• vaccinating pets

• keeping pets away from wild animals

• protecting small animals from predators

• report stray animals to locat authorities

• keep bats out of your homes

• don’t approach wild animals

Arbovirus properties

• arthropod borne virus

• transmitted by blood feeding arthropods

• Host: humans and other vertebrates

• more prevalent during warm weather

Types of arbovirus and relevant veterinary disease

• Bunyavirus: Rift Valley Fever, Cache Valley Fever, Hantavirus pulmonary syndrome

• Flavivirus: West Nile Virus

Arbovirus vectors and reservoirs

• Vectors: flies, mosquitoes, ticks, midges

• Reservoirs: birds, arthropods and vertebrates (rodents, monkeys, humans)

Arbovirus transmission

• non-human reservoirs → humans

• human → human via blood transfusion, organ transplant, sexual contact, transplacentally

Bunyavirus properties

• enveloped

• single stranded

• replication: cytoplasm

• vectors: arthropods/rodents

Bunyavirus infection characteristics

• cytocidal infection in mammalian cells

• non-cytocidal ane persistant infection in invertebrate cells

• genetic reassortment occurs between closely related bunyaviruses

Bunyviruses of veterinary importance

• Rift valley fever virus

• Cache valley fever virus

• Humans: Hantavirus

Bunyavirus pathogenesis

• entry

• local replication

• invasion of liver and other major organs

• wide spread necrosis

Rift valley fever

viral zoonosis that primarily infects animals but can infect humans

Rift valley fever pathogenesis

• disease outbreaks

• heavy rain

• increase in breeding of vectors

• disease outbreak

Rift Valley Fever transmission

• mosquitoes

• transovarial between vectors

Animal hosts of Rift Valley Fever

• sheep, goat, cattle

• sheep most susceptible

• death and abortion storms in livestock

Diagnosis of Rift Valley Fever

• histopathological lesion of liver

• immunohistochemistry

• detection of viral antigen in serum by ELISA

• Viral RNA detection in serum and tissues and mosquitoes by RT-PCR

• antibody detection in serum by ELISA

Diagnostic samples for Rift Valley Fever

• blood from viremic animals

• fetal organs

• tissues: liver, spleen, and brain

Rift valley fever prevention

• vaccinate animals

• human: appropriate PPE, insect repellants

Cache valley fever

zoonotic, transmitted to humans only by mosquito bites and not direct contact with infected animals

Cache valley fever host and vectors

• host: small ruminants

• vector: mosquito

Cache valley fever clinical signs

• abortion

• congenital malformations of fetus

Cache valley fever pathogenesis

• enters host body

• crosses placental barrier

• infect kids and lambs in utero

Cache valley fever prevention

• no vaccine/treatment

• insect control

Diagnosis of cache Valley fever

• clinical signs: increased number of open ewes

• post mortem lesion: congenital malformation of fetus

• antibody testing:

  • serological testing of dams

  • fetal fluid antibody testing: heart blood, pericardial, pleural effusion

Hantavirus

• host: humans

• vector: rodents

• pets and livestock do not get ill from hantavirus

• keep pet rodents away from wild rodents

Flavivirus properties

• enveloped

• spherical

• vectors: ticks and mosquitoes

• replication: cytoplasm

Flaviviruses of veterinary importance

• West Nile Virus

What are the most suceptible host for flaviviruses?

Corvids (blue jays, crows, ravens)

WNV in horses clinical signs

• asymptomatic or flu-like

• neurological signs or encephalomyelitis

WNV diagnosis

• clinical signs: neurological disease

• ELISA test: antibody detection

• blood samples

WNV treatment

supportive care

WNV prevention

• core vaccine

• mosquito control

WNV in birds

• clinical signs: loss of coordination, head tilt, tremors, weakness

• diagnosis: heart, brain, kidney tissues, oral swabs

• prevention: vaccines

Coronovirus properties

• enveloped

• replication: cytoplasm

• helical nucleocapsid

Coronaviruses of veterinary importance

• Feline: Feline Infectious Peritonitis

• Dogs: Canine corona virus infection

FIP overview

• cats between 3 months and 6 years most susceptible

• strains found in GI tract (FeCV) do not cause major clinical disease

• FECV mutates to form FIP, severe inflammation in abdomen, kidneys, brain

FIP transmission

• fecal oral

• fomites

• feces

• asymptomatic or carrier animals

2 Forms of FIP

• wet form: fluid accumulation in abdomen, difficulty breathing

• dry form: neurological signs; severe inflammation of eyes, brain, liver, intestine

FIP diagnosis

• no definitive test to diagnose FIP

• FA test: lung, liver, brain, kidney, soleen

• PCR

• antibody test

FIP prevention

• vaccination: healthy cats >16 weeks of age

• keeping small groups of cats (4 or less)

• avoid stress

• good hygiene

Canine coronavirus

• canine enteric coronavirus: mild and self-limiting diarrhea

• canine respiratory corona virus: part of kennel cough complex

Canine enteric coronavirus

• highly contagious and infectious intestinal infection in dogs

• treansmission:

  • direct contact with infected dogs

  • fecal oral

  • contaminated food bowl

• disinfection

• diagnosis: IFA titration, serum samples, virus isolation, PCR, FA test intestine

Canine respiratory coronavirus

• highly contagious illness affecting respiratory tract in dogs

• transmission:

  • dog to dog contact

  • aerosols of respiratory secretions

  • contaminated environments

• susceptible: boarding kennels

• management: isolation, biosecurity, sanitation

• Diganosis: IFA titration of serum samples, virus isolation, PCR

What are prions?

• proteinaceous infectious material

PRPC

• endogenous prion

• properly folded

• present in normal brain and diseased brain

• does not cause disease

PRPSC

• not present in normal brain

• improperly folded

• present in diseased brain

• causes disease

Prion diseases/transmissible spongiform encephalitis:

• cattle: mad cow disease

• sheep: scrapies

• mule, deer, elk: chronic wasting disease

• Cat: feline spongiform encephalopathy

• human: vCJD

Transmissible spongiform encephalitis

• progressive neurological disease

• damages brain and spinal cord

• transmission: ingestion of feed material containing abnormal prion

• not contagious

• month to years incubation period

• no treatment, no vaccine

Mad cow disease

• fatal neurodegenerative brain disorder affecting cattle

• prevention:

  • cull infected animals

  • do not use feed products containing CNS material as livestock feed

Scrapie

• fatal disease in sheep

• reportable

• when purchasing new animal, ensure it is part of scrapie certification prevention program

Chronic wasting disease

• hunters should consider testing carcass for CWD

• do not eat or feed positive meats

• wear gloves when field dressing a carcass