Virus 4 (RNA): Rabies Flashcards
What are the characteristics of the virus causing rabies?
- kills up to 50k people/yr, mostly in Asia
Which animals act as a reservoir for rabies?
- Dog, bat, fox, skunk, raccoon, mongoose, etc.
- most warm blooded animals
- Kills dog within 2/52 – so dogs can be impounded to see if they die. If infected, dog rushes around, high pitched bark, salivating lots
- But human transmission is nearly all domestic dog, few bats in USA/Europe
- There is bat virus in UK: Must get PEP.
- Can result in livestock death too -> large economic losses in South America
- dogs can be given high degree of proteiction through live attenuated vaccine.
How does rabies virus infect humans?
Transmission
- Latent period usually 1 - 3 months but can be up to a year – This varies depending on distance from head/brain + size of inoculation bite
- Uptake into peripheral nerves and retrograde neuronal spread
- Spread to CNS and salivary glands is then very rapid and clinical signs appear
- Death within 7 days of clinical signs appearing Infectivity
- Not infective during latent period (asymptomatic)
- But up to the last 10 days of the latent period can be infective
- Clinical signs/behavioural change – death within days
• If bitten by rabid animal chances of contraction are around 15%
- usually transmitted through bite, salivary contamination of cuts, occasionally by inhalation
What are the clinical manifestations of rabies?
Two forms of rabies: furious and paralytic
Furious:
- Behaviour change. Delirium/Encephalitis – aggression/biting
- Excess salivation
- Muscle tremor, incoordination, seizure
- Hydrophobia, Aerophobia [neither present in animals]
- Paralysis, coma, death
Paralytic:
• About 20% have paralytic rabies with ascending weakness
How can we diagnose rabies?
Presumed infection until proven otherwise / clinical diagnosis
• Skin biopsy [nape of neck]: PCR, virus antigen detection [immunofluorescence] •
Saliva: PCR, virus isolation
• CSF & brain biopsy: virus isolation, eosinophilic Negri body inclusions
How do we protect ourselves from rabies patients?
- patients saliva is infectious
- barrier nursing, inlsive of visors
- staff sould receive rabies immunisation (four injection of human diploid cell vaccine, one in each limb all in same day)
What do we use for pre-exposure vaccination?
- travellers to endemic areas and those at special risk (e.g. vets)
Available for humans and animals
- It is a 3-dose regimen intradermal/IM for humans
- For animals it can be oral and contained in a bait – if you prevent it in your main reservoir host you remove it i.e. fox in Europe
- It is cheaper to have a dog vaccine policy and cover rural communities too
How do we treat rabies patients, e.g. those with symptoms?
- invariably fatal
- heavy sedation, ITU care
How do we treat those who have been bitten?
Wash the wound or the scratch with soap and water and inject as much RIG as you can into the area as soon as possible.
A viricidal solution, e.g. povidone-iodine solution or cetrimide (0.15%), should also be used locally. Animal studies confirm that this reduces the likelihood of transmission and, it is widely held, that in man the earlier the area is cleaned and RIG given, the less chance the patient has of contracting the disease.
Heavy sedation, tetanus prophylaxis, antibiotics and general supportive measures can make things easier for the patient and for the family in established cases. Barrier nursing in an isolation suite should be provided if at all possible.
A full protocol for post-rabies prophylaxis in immunized and non-immunized patients is available on the WHO and CDC websites and in the UK, Dept. of Health ‘green book’.
RIG (rabies immune globulin) is only used if the person involved is either not immunized or incompletely immunized. Human RIG (HRIG) should be used, not the very allergenic equine derived product. HRIG is not widely available and is expensive.
Should the offending animal be caught and survive for 15 days in quarantine then one is certain that the animal is rabies free. However in practice the majority of people who are bitten are far too frightened and panicky to trap their attacker. Consult Table 36.2 in Tropical Medicine Lecture Notes.
How can we eliminate rabies?
Domestic dogs are the perpetuating host
- Rabies R0 value is low: R0 = 1-2
- Culling dogs is proven to be ineffective
- Dog Vaccination = Elimination of Human Rabies
Public Health Essay Question Rabies
There have been a number of deaths in a small community in the Philippines and the description of cases is suggestive of a cluster of rabies cases.
a) What methods could you use to confirm the diagnosis of rabies (2)
b) Describe a programme that aims to eliminate rabies in this area (14)
d) What obstacles might you face (4)
Clinical
• Public education –
o Reservoir: wild animals + dogs – signs to look for o Avoid contact/biting
o Advice to seek care immediately if bitten
- Train HCW in diagnosis/treatment – wound cleaning, vaccine, immunoglobulin
- Drug supplies at local healthcare facilities: vaccine, immunoglobulin, antibiotics, tetanus, wound-care packs including antimicrobial wash
- Consider mass vaccination of local population
- Surveillance and reporting system for cases
Veterinary
- Train veterinary workers in dog vaccination/baited vaccination
- Public education – to bring all dogs for vaccination
- Mobile dog vaccination units for domestic and stray dogs
- Baited vaccines for wild animal population • Secure veterinary vaccines
- Surveillance, reporting system and facilities for humane animal euthanasia
How do you define a zoonotic disease?
A zoonosis is any disease that is normally endemic in animals but which can be transmitted from animals to humans. The offending organism in a zoonotic disease can develop fully in non-human hosts (wild or domestic animals).
In some cases the disease can be transmitted from man to animals (reverse zoonosis). In a strictly zoonotic disease there is no human-to-human transmission.
In multihost disease, the offending organism can develop fully in both human and non-human hosts and, crucially, human-to-human transmission as well as species jump may occur.
