Key Microbial agents causing neurological disease 1 Flashcards
Why would someone need to go through post exposure prophylaxis after being bitten by a rabid animal?
- Immediately wash/flush/disinfect the wound post bite
- Even if you have titres, you still recieve another vaccine
- You would then receieve an anti-rabies immunoglobulin which provides immediate source of antibodies against rabies
What is meant by pre-exposure prophylaxis for rabies?
- Vaccination – vaccines are safe and effective
- Maternal antibody interference - 1st vac at 3 mths
- Titre testing used to determine vaccine effectiveness
- Oral recombinant vaccine (Raboral V-RG ®) used successfully in wildlife
Explain the pathogenesis of rabies.
- Infection is by direct inoculation of infectious saliva from rabid animal into bit would OR abrasion - massive amounts of virus in saliva
- Initial inoculation via bite or open wound +/- replication in peripheral tissues (eg myocytes and subcutaneous tissue)
- Moves along nerves (centripetally) to the CNS
- Dissemination within CNS (Neurotropic virus) with replication in brain resulting in clinical signs
- Centrifugal spread to various organs, especially salivary glands
- Centrifugal spread from CNS to various organs especially salivary glands
What is the incubation period of rabies?
Anywhere from 2 weeks (typical time) to 3 months but can be longer.
Is there a phase that happens prior to clinical signs in rabies?
Yes, this is called the prodromal phase that may occur a few days prior to overt clinical signs
- Change in temperament
- pruritus and licking at site of bite
What are the two forms of rabies?
Furious (psychotic) and dumb (paralytic)
What are the signs associated with the furious form of rabies?
Restless and irritable
Hyperaesthetic
Aggression
Excessive salivation – unable to swallow
Pica
Progressive neurological dysfunction
Seizures
May die or progress to dumb form
What are the signs associated with the dumb form of rabies?
LMN (lower motor neuron) paralysis – beginning at site of inoculation
Excessive salivation / dropped jaw
Change in vocalisation
Dull
Coma
Death – respiratory failure
Is there any treatment for rabies?
No, there is no known effective treatment for clinical rabies
What are some ways that rabies can be controlled?
All dogs and cats should be vaccinated against rabies according to local rules and regulations of the country and state
What would happen if a pet had been bitten by a rabid animal and the pet was NOT vaccinated?
- Depending on the legislation, the pet would likely be euthanised and submitted for rabies testing OR if owner doesnt want that then the pet should be strictly quarantined for 6 months with vaccination one month prior to release
What would happen if a pet had been bitten by a rabid animal and the pet WAS vaccinated?
Re-vaccinate and quarantine for 90 days
What are the characteristics of the rabies virus?
- Enveloped, single stranded negative sense RNA virus with characteristic bullet shaped virion
- Sensitive to drying and UV light but stable in cold dark places (e.g. caves)
- It has a broad host range - infects ALL mammals (though susceptibility varies)
- MOST lethal of all viral infections
What are the resovoir species for rabies?
A variety of mammalian reservoir species maintain and transmit rabies virus variants
o Canidae – dogs, foxes, wolves etc.
o Mustelidae – skunks, weasels
o Viverridae – mongooses
o Procyonidae – raccoons
o Chiroptera - bats
Distinct genotypes/strains based on host species – e.g. dog rabies, racoon rabies
o Transmitted best between host species, but can still infect any mammal
How would you diagnose rabies?
- Based on compatible history and clinical signs
- ante-mortem tests in humans are unreliable
- GOLD STANDARD: Viral antigen in brain tissue (direct immunofluorescence and immunohitochemistry)
- Histology: negri bodies - not always presnet
- RT-PCR: brain tissue, and saliva and urine are less sensitive
- Measuring antibodies is unreliable
How would you diagnose rabies?
- Based on compatible history and clinical signs
- ante-mortem tests in humans are unreliable
- GOLD STANDARD: Viral antigen in brain tissue (direct immunofluorescence and immunohitochemistry)
- Histology: negri bodies - not always presnet
- RT-PCR: brain tissue, and saliva and urine are less sensitive
- Measuring antibodies is unreliable
What rabies virus is present in Australia?
- Australian bat lyssavirus - pathogenesis is identical to the other forms
- There have been 4 reported deaths from 1996 in humans in Australia
What are the features of the family Paramyoviridae?
- Single stranded negative sense RNA
- Enveloped virus - Very fragile in environment
- Major glycoproteins on envelope (H, HN, or G, and F) important for viral attachment and fusion between cells, and for host immune response - less antigenic variability of glycoproteins compared with Orthomyxoviridae
- Cell mediated immunity essential for control of infection
Describe the pathogenesis of canine distemper virus.
- Transmission via contact with droplets
- Dogs with acute distemper excrete virus in conjunctival and nasal exudates as well as faeces, saliva and urine.
- Initially replicates in oropharynx (usually tonsils) then spread throughout body via a cell mediated viraemia
- Proliferation in lymphoid tissue (first fever peak)
- Subsequent viral invasion of epithelial tissues (e.g. respiratory, gastrointestinal, urogenital) and/or the central nervous system
- is dependent on the dogs humoral and cell mediated immunity and the virulence of the virus.
- Shedding of the virus begins when the virus replicates within the epithelial tissue and this occurs even in subclinical infections
What forms of canine distemper virus are seen? What are the clinical signs associated with these forms?
- Asymptomatic
-
Acute
* Biphasic fever with second peak T=41°C
* severe leucopaenia
* Respiratory disease
o catarrhal inflammation of larynx, bronchi, tonsils, nasal passages
* Conjunctivitis (purulent)
* Gastrointestinal disease
o vomiting, watery diarrhoea
* CNS disease
o behavioural changes, spasms, ataxia, paresis
* Combination of respiratory tract and GIT disease in young unvaccinated dog think distemper -
Subacute
* Encephalitis
* Seizures
* +/- other signs -
Chronic
* Can occur even if initial infection subclinical
* Old dog encephalitis
o Slow progressive loss of motor function
* Hard pad disease
o hyperkeratosis of nasal planum and pads
How is canine distemper diagnosed?
- Based on clinical signs
- Real time RT-PCT (acute phases - buddy coat or conjunctival swab, chronic cases - urine, whole blood, serum or CSF)
- IFA on ocular or nasal discharges - early stages only
- Biopsy on footpads, conjunctiva, bladder and skin of dorsal neck to reveal inclusion bodies (things the virus leaves behind)
- immunohistochemistry is sometimes required
How is canine distemper controlled?
- Despite being an RNA virus, surface glycoproteins are relatively stable
- Vaccination have been very effective (live attenuated)
- because of disease in wildlife (lions, hyenas) zoo animals need to be vaccinated
What animals can be infected with canine distemper?
- Canidae – fox, wolf, coyote, dingo
- Ursidae – bear, giant panda
- Procyonidae – racoon
- Felidae – cheetah, lion, jaguar (NOTE: Feline distemper ≠ canine distemper. Domestic cats can be experimentally infected with CDV but infection is asymptomatic. The term feline ‘distemper’ is an older term given to disease caused by feline panleukopaenia virus (i.e. feline parvovirus))
- Mustelidae – ferret, weasel, mink, skunk
How is canine distemper treated in ferrets?
Its not, the disease is fatal
How can canine distemper virus be controlled in ferrets?
Vaccination - 1/6 dose to 1/2 dose of the dog
