Rabies

Epidemiology and control of Rabies

Epidemiology & control of communicable disease

Learning Objectives

At the end of this lecture you should :
Know the causative agent , reservoir of infection , mode of transmission, Incubation period, clinical presentation and outcome of infection.
Know the control measures of rabies
Have detailed knowledge regarding post-exposure prophylaxis for patients who may have been exposed to the disease through animal contact.

Rabies:

Rabies is acute viral infection of the central nervous system. It is primarily a disease of animals, affecting both wild and domestic animals but it can be transmitted to humans.

Causative Agent:

Rabies virus
Member of rhabdo-virus family
Enveloped, single-stranded RNA genome
Bullet shaped


Reservoir of infection:

Domestic & wild animals mainly dogs, foxes, wolves, cats, bats, jackals , raccoons, Skunks , Cattle ...etc

Epidemiology

World wide distribution
It is estimated that approximately
55 000 persons die of rabies each year.
The regions most affected are tropical developing countries within Asia, Africa and Latin America, where over 99% of all human rabies deaths occur.

In Animals

Rabies is a zoonosis which is prevalent in wildlife(natural world_). The main animals involved differs from continent to continent.
Europe foxes , bats
Middle East Wolves, dogs
Asia dogs
Africa dogs, mongoose
N America foxes, skunks, raccoons,
insectivorous bats
S America dogs, vampire bats



In many industrialized countries, animal rabies has been brought under control.
WHO considers some countries as Rabies free countries like: UK, Iceland , Japan , Spain, Portugal, Greece, Sweden, Finland and Norway.

Transmission:

Rabies virus which is present in the saliva of infected animals can be transmitted to humans by:
A bite or scratch that punctures the victim's skin.
Airborne transmission in bats’ caves was also reported .
Human rabies transmitted by corneal transplant was also reported

Incubation Period: may vary from few days to several years (the average is 20 -90 days).

IP is influenced by:
Severity of the wound (size and depth of the wound)
Infective dose & strain of the virus.
Site of wound (degree of innervations and its distance from the brain - the farther from the brain, the longer the incubation period)

Clinical features:

At the beginning the patient complains of malaise, loss of appetite, fatigue, headache, and fever.
More than 50% of patients have pain or itching and sometimes numbness at the site of the wound.

Two to 10 days later, signs of nervous system damage appear, anxiety, confusion, agitation, hydrophobia (fear of water), disorientation, hallucinations, seizures, paralysis and coma.


Death may be sudden, due to cardiac or respiratory arrest, or follow a period of coma that can last for months.
Outcome of the disease
Rabies is a fatal disease; it cannot be treated once symptoms appear
World wide up to date only six known survivors of the disease

Diagnosis

Histopathology- Negri bodies are pathgnomonic of rabies. However, Negri bodies are only present in 71% of cases.
Rapid virus antigen detection- virus antigen detection by Direct Fluorescent Antibody test (DFA) is commonly used.
Virus cultivation – The most definitive means of diagnosis is by virus cultivation from saliva and infected tissue. Cell cultures may be used or more commonly , the specimen is inoculated intracerebrally into infant mice.

Control of Rabies

The Control of Rabies involves two separate measures:
The control of the Disease in animals (control of reservoirs)
The control or Prevention of the disease in man

Control of rabies in animals

Immunization of domestic animals
Control of stray dogs
In addition in rabies free countries, quarantine of imported animals for 6 months

Prevention of Rabies in Man

This can be done by:
General Precautions to Avoid exposures to the risk of Rabies
Providing pre-exposure immunization to people at high risk for being exposed to rabies; and
Giving post-exposure preventive measures to people who may have been exposed to the virus.

General Precautions to Avoid Rabies Exposures

People should be advised to:
1. Consider mammals larger than a rodent especially wild animals, as potentially infected with rabies.
2. Handle the following animals with extreme care : dogs, cats (especially feral dogs and cats), skunks, raccoons, foxes, and bats.
3. Wear appropriate protective clothing, gloves, and eye protection when working with any of the above animals.


Report Immediately any bites or scratches from animals . So, bites or other exposures can be evaluated as soon as possible by a physician to ensure proper post-exposure treatment is administered promptly.

Pre-exposure Prophylactic measures

All people at high risk of exposure to rabies should receive pre-exposure vaccination which include:
3 doses of rabies vaccine
on days 0, 7, and 21 or 28.
Each dose is 1 ml given IM in the deltoid area -


Three types of vaccines are available:

Human Diploid Cell Vaccine (HDCV)

Rabies Vaccine Adsorbed (RVA)
Purified Chick EmbryoCell Culture Vaccine (PCECV)

The high risk groups are:

Veterinarians and their staffs
Animal control personnel
Laboratory workers doing rabies diagnostic tests
Persons who have frequent and close contact with wild animals

Post-exposure Prophylaxis

This is for people who may have been exposed to the virus (after animal bite)This includes :
Prompt local treatment of the wound Local wound care ( thorough cleansing of the site with soap and water). Bite wounds are not sutured unless very severe due to the high risk of bacterial infection.

Passive immunization with rabies immunoglobulin

Provision of passive immunity by Human Rabies immunoglobulin (HRIG) ,20 IU /kg body wt , half the dose in and around the wound and the other half IM

Active immunization with vaccine Vaccination: five 1 ml doses of rabies vaccine given IM in the deltoid area, on days 0,3,7,14 and 28
Booster dose of Tetanus toxoid vaccine should be given if indicated
Antibiotics to prevent secondary infection


If Previously vaccinated
Local wound care, Tetanus toxoid, and antibiotics
No need for HRIG
Vaccination: two doses ,on days 0,3

Post-exposure Prophylaxis Regimens

NotPreviouslyVaccinated:

Day0

Day3
Day7
Day14
Day28

wound care

x

HRIG

x


Vaccine
x
x
x
x
x
PreviouslyVaccinated:

wound care

x

HRIG

Vaccine
x
x

Post exposure prophylaxis for rabies

Animal
Condition of animal
Post exposure prophylaxis(PEP)
Dog &cat
Healthy & available for observation for 10 days
PEP at first sign of rabies in dog or cat


Rabid or suspected Rabid
PEP immediately

Escaped and cannot be found

PEP immediately
Wild animals
Regarded as rabid
PEP immediately

Thank you