Rabies 1234

Presented By: Dr. Md. Salequr Rahman

Dep. Of Community Medicine

Acute highly fatal viral disease of central nervous system, caused by Lyssavirus type 1.

Primarily a zoonotic disease of warm blooded animals (Dogs, cats, jackals and wolves).

Transmitted to man by bites or licks of rabid animals

Rabies (Hydrophobia)

Classical hydrophobia is clinically characterized by a long and variable incubation period, a short period of illness due to encephalomyelitis ending in death, despite intensive care.

Only communicable disease that is always fatal. 35,000-40,000 human deaths occur in SEAR

countries. Bangladesh and India belong to the high incidence countries.

Agent: Lyssavirus type 1- it is a bullet shaped neurotropic RNA containing virus. It is a large virus. The virus is excreted in the saliva of rabid animals. The virus available from naturally occurring cases are called

Street Virus”. Incubation period is 20-60 days in dogs. Introduction of street virus into rabbit modifies the virus as its incubation period is reduced to 4-6 days. Virus isolated at this stage is called a “Fixed Virus”. This is used for preparation of vaccine. The intracytoplasmic inclusion bodies named as “Negri bodies” represnt a colony of virus particles within the nerve cell. Negri bodies contain infectious agent. Fixed virus does not produce Negri bodies.

Urban rabies: Infection from wild life to domestic dogs, responsible for 99% of human cases. A single rabid dog is capable of biting large number of human, animals and may involve an area of 40 km. Cats may be a source.

Wild life rabies: Sylvatic form. In jackal, fox, hyena and other life carriers.

Bat rabies: Vampire bat is an important host and vector of rabies (in Latin American countries)

3 Epidemiological forms of Rabies:

Source of infection: Saliva of rabid animals.

Host factors: Laboratory staff, veterinarians, dog handlers, hunters, field naturalists.

Animal bites Licks on abraded skin and mucosa Aerosols Person to person: rare.

Mode of transmission:

What kind of animals get Rabies?

The rabies virus can infect all mammals.

Mammals are warm-blooded animals that have hair and mammary glands to produce milk for their babies.

Animals like frogs, birds, and snakes do not get rabies.

3-8 weeks; vary from 4 days to many years. IP tends to be shorter in severe exposures and bites on face, head and upper extremities and bites by wild animals.

Incubation period:

Virus replicates in muscles and connective tissues at or near the site of introduction before it attaches to nerve endings and enters peripheral nerves. Spreads from site of infection centripetally via the peripheral nerves towards the CNS; then centrifugally in peripheral nerves to many tissues including skeletal and myocardial muscles, adrenal glands and skin.

Pathogenesis:

Rabies – A fatal Zoonotic Disease

Dr.T.V.Rao MD 14

Man’s best friendbut can spread Rabies if not vaccinated

Prodromal symptoms: Headache, malaise, sore throat and slight fever lasting for 3-4 days. Complains of pain and tingling at the site of bite.

This stage is followed by widespread excitation and stimulation of all parts of nervous system- sensory, motor, sympathetic and mental.

The patient is intolerant to light, noise or cold draught of air. Aerophobia may be present and pathognomic.

Clinical features:

Dr.T.V.Rao MD 18

On examination: increased reflexes and muscle spasm along with dilatation of pupils and increased perspiration, salivation and lacrimation (sympathetic).

Mental changes include-fear of death, anger, irritability and depression.

Clinical features:

The symptoms are progressively aggravated and all attempts of swallowing liquid become unsuccessful. At later stage the mere sight/sound of water may provoke spasm of muscles of deglutition. The characteristic symptom of hydrophobia is pathognomic of rabies.

Duration of illness 2-3 days. Only three people are on record who survived.

Clinical features:

H/O bite Characteristic S/S Virus isolation in saliva

Diagnosis:

Isolation Sedation Hydration, diuresis Respiratory, cardiac support Muscle relaxants

Rx:

Fixed virus grown in neural tissues of rabbits, ships, goats, mice, rats, in embryonated duck eggs, cell cultures.

NTV (SHEEP) DEV Cell culture vaccine1. HDC vaccine2. 2nd generation tissue culture

Vaccines:

Nervous tissue vaccine: 14 injections (5 ml each) are given deep s/c

around the umbilicus for 14 days. S/E: Ascending type of paralysis and post

vaccinal encephalopathy.

Vaccines:

Propagating the rabies fixed virus in human diploid fibroblast cells. Generally safe and highly potent. I/M injection of 5 doses of 1 ml in deltoid region; first as soon as the bite; other doses on 3, 7, 14, 28 days and booster dose on 90th days.

HDCV:

Intradermal vaccine schedule (WHO): (0.1 ml)

Vaccine schedule followed in Infectious disease hospital-

Dose day1st o 2 in 2

arms2nd 3rd 2 in 2

arms3rd 7th 2 in 2

arms4th 28th 2 in 2

arms

Intramuscular Vaccination schedule:( 0.5-1 ml)

1st 0 2 in 2 arms

2nd 7th one in one arm

3rd 21st one in one arm

Post exposure prophylaxis Pre exposure prophylaxis Post exposure Rx of persons who have been

vaccinated previously.

Prevention of human rabies:

1. General consideration: The aim is to neutralize the inoculated virus before it can enter the nervous system. Every exposure should be treated as medical emergency. It is established that irrespective of the class of wound, the combined administration of a single dose of anti rabies serum with a course of vaccine, together with local treatment of wound is the best specific prophylactic treatment after exposure of man to rabies.

Post exposure prophylaxis:

Cleansing-immediate flushing and washing the wounds, scratches and the adjoining areas with soap and detergent and water, preferably under a running tap, for at least 5 minutes. Then cleansing with alcohol or povidone iodine. Local wound treatment can reduce the chances of developing rabies up to 80%.

Anti rabies serum locally Antibiotics and anti tetanus measures3. Immunzation

2.Local treatment of wound:

POSTEXPOSURE PROPHYLAXIS

1 – Wound cleaning & treatment

If the animal has signs of rabies and dies within 10 days of observation

If the biting animal cannot be traced. Unprovoked bite. Lab. test (florescent rabies antibody or test for

negri bodies) of the biting animal are positive for rabies.

Wild animals.

Indications for anti rabies treatment:

Category 1: touching /feeding animals, lick on intact skin( no exposure) [No prophylaxis is required]

Category 2: Nibbling of uncovered skin, minor scratches/ abrasions without bleeding [immediate vaccination]

Classification of wounds/exposures:

Category 3: Single/multiple trans dermal bites/ scratches, contamination of mucus membrane with saliva from licks, licks on broken skin, exposure to bats[immediate vaccination+ administration of rabies immunoglobulin]

Presented By: Dr.

Dep. Of Community Medicine