In this essay we will discuss about Rabies. After reading this essay you will learn about:- 1. Introduction to Rabies 2. Morphology of Rabies 3. Antigenic Structures of Rabies 4. Laboratory Diagnosis of Rabies 5. Prophylaxis of Rabies 6. Dose Schedule of Vaccine for Rabies 7. Prevention and Control of Rabies 8. Vaccine for Rabies.
Contents:
- Essay on the Introduction to Rabies
- Essay on the Morphology of Rabies
- Essay on the Antigenic Structures of Rabies
- Essay on the Laboratory Diagnosis of Rabies
- Essay on the Prophylaxis of Rabies
- Essay on the Dose Schedule of Vaccine for Rabies
- Essay on the Prevention and Control of Rabies
- Essay on the Vaccine for Rabies
Contents
- Essay # 1. Introduction to Rabies:
- Essay # 2. Morphology of Rabies:
- Essay # 3. Antigenic Structures of Rabies:
- Essay # 4. Laboratory Diagnosis of Rabies:
- Essay # 5. Prophylaxis of Rabies:
- Essay # 6. Dose Schedule of Vaccine for Rabies:
- Essay # 7. Prevention and Control of Rabies:
- Essay # 8. Vaccine for Rabies:
Essay # 1. Introduction to Rabies:
Rabies is primarily a disease of animals caused by neurotrophic virus. It is a dreaded viral zoonotic disease known to mankind since antiquity before 2,300 BC. It has been reported that over 3 million persons are bitten annually by dogs in India. Over 30,000 Indians die of Rabies every year. It is incurable but preventable by immuno-prophylaxis.
Essay # 2. Morphology of Rabies:
(1) Under electron microscope, Rabies (Latin rabidus to rave) viruses (Fig. 49.1) are large rod or bullet-shaped (rhabdos, meaning rods) measuring 76 x 175 nm.
(2) Nucleo capsid shows helical symmetry and contains a single stranded un-segmented RNA genome and viral transcriptase.
(3) Outer lipoprotein envelope contains producing haem-agglutinating peplomer spikes, 10 nm long.
Rabies virus is bullet shaped. It forms eosinophilic intracytoplasmic inclusion bodies in the nerve cells of the hippocampus—known as “Negri bodies” which are specific in rabies infection and enable a diagnosis of rabies.
Rabies virus is more resistant to disinfectants: 0.5 per cent formaldehyde fails to kill in two months at 4°C; but 1 per cent formaldehyde, 3 per cent cresol and 0.1 per cent mercuric chloride inactivate in 15 minutes; also it is inactivated at 60°C in 10-15 minutes. It is destroyed by a 5 per cent phenol solution and other disinfectants.
Essay # 3. Antigenic Structures of Rabies:
Rabies viruses of man and animals all over the world appear to be of a single antigenic type:
(a) G. protein: The envelope glycoprotein is strongly antigenic and antibody against G. protein is protective. It induces and reacts with virus neutralizing antibody.
G. protein also stimulates T-lymphocytes expressing helper, suppressor or cytotoxic activity. Antibody to G protein lyses infected cells in presence of complement.
(b) M. protein (internal membrane protein) and N. protein (nucleoprotein) have no virus neutralizing activity.
(c) Haemagglutin (NA) has haem-agglutinating activity with goose erythrocytes.
Pathogenesis and Disease in Man:
The portal of entry is the bite and the rabies virus in the infected saliva is introduced into the wound or scratch or abrasion contaminated by saliva. The virus multiplies locally in the tissues, invades the damaged nerve fibres and spreads centrally to reach the brain and spinal cord.
The incubation period is ten days to two years after the bite of rabid animals, its duration depends on the distance between the point of entry and the brain: bite on the legs, 60 days; on the arm, 40 days; on the head, 30 days. It is short in children than in adults.
The first symptoms of the disease are headache, fever, a profound sense of apprehension and a feeling of irritation at the site of the bite. The patients complain of dry throat, but they will not drink. High fever, difficulty in swallowing and a fear of water (hydrophobia) become dominant symptoms and the patient passes into delirium with generalized convulsion. The outcome is invariably death.
Essay # 4. Laboratory Diagnosis of Rabies:
First diagnosis should be made in rabid animals.
(I) Then diagnosis in man should be carried out on the basis of clinical findings. Rapid immunofluorescence test can detect viral antigen in skin biopsy or in corneal impression smear. Virus can be isolated from saliva and CSF. Antibodies to virus appear very slowly.
Postmortem Diagnosis can be done by:
(a) Demonstration of Negri bodies in hippocampus major of brain (80% positive) of animals or men died of rabies.
(b) Isolation of virus by mouse inoculation with infected brain, CSF, saliva and urine.
(c) Immunofluorescence test can detect viral antigen in impression smear.
(II) Diagnosis in Animal:
First one must wear hand glove and remove very carefully the brain of rabid animal. One part of the brain should be preserved in 50% glycerol saline for isolation of virus and another part in Zenker’s fixative for Negri bodies demonstration.
Steller’s staining technique (basic fuchsin and methylene blue in alcohol) can reveal Negri bodies in brain which are round or oval, purplish pink (acidophilic) structures within the cytoplasm of nerve cells.
Essay # 5. Prophylaxis of Rabies:
It may be (A) Pre-Exposure Prophylaxis;
(B) Post-exposure prophylaxis.
(A) Pre-Exposure Prophylaxis:
This is carried out in persons who handle severely infected animals and is given intradermally at monthly intervals and followed by yearly boosters.
(B) Post-Exposure Prophylaxis:
Rabid dog/animal bite wound should be immediately washed with plenty of water and soap or water with potassium permanganate, then with quaternary ammonium detergent (cetavlon) or tincture of iodine or alcohol.
Damaged tissue debris should be removed and wound should not be sutured. The suspected animal should be under strict isolation/observation for 10 days under veterinarian through public health office. If the animal remains alive without any symptom for more than 10 days, rabies can be excluded. If rabies is suspected, post-exposure prophylaxis should be adopted by
(i) Hyper-immune serum, and
(ii) Vaccine.
Essay # 6. Dose Schedule of Vaccine for Rabies:
(a) In Europe HDCV vaccine 1 ml is given intramuscularly on days 0, 3, 7, 14, 30 and 90. HDCV is only licensed vaccine in U.K. and USA.
(b) In India HDCV is recommended rabies vaccine available in market and is costly. So people prefer less costly Sample or BPL vaccine.
Vaccine for Animal:
Cell culture vaccine containing BPL is adsorbed on aluminium hydroxide before vaccination. A simple dose of 0.1 µl is given intramuscularly, followed by booster at 1-3 years’ interval.
Essay # 7. Prevention and Control of Rabies:
Vaccination of domestic dogs by a Flury (Live) canine vaccine, and destruction of stray dogs are most effective control measures. In bats, the virus may remain as latent infection for long time. Man may get the infection by inhaling, contaminated dust in caves housing infected bats. Man should wear mask while frequenting old abandoned house or cave.
Essay # 8. Vaccine for Rabies:
Passive immunization:
In case of severe bites, anti-rabies serum or hyper-immune horse serum is injected for passive protection around the bite wounds.
Active immunization:
Various vaccines are used to confer active immunity.
(i) Sample vaccine:
Which contains a 4 per cent suspension of the brain of sheep infected with the “fixed virus” inactivated by 0.5 per cent phenol. This vaccine has a drawback that it may contain nervous tissue which may sensitize a small proportion (1 : 4,000 to 1 : 10,000) of person who may develop an allergic type of encephalitis.
(ii) Avianised vaccine:
Contains no nerve tissue, it avoids the neuroparalytic accidents. The inactivated duck embryo vaccine was first introduced in United States of America and is mainly used in Britain; it is less effective than brain tissue or tissue culture vaccine.
A similar vaccine prepared from Rabies virus grown in primary chick embryo cell culture and purified to remove cell proteins and nucleic acids has been made available in India through Hoechst India Ltd., Mumbai. It is given intramuscularly one dose (1 ml) in the deltoid muscle of alternate arms on days of 0, 3, 7, 14, 30 and 90 days. O indicates the day of the first dose.
(iii) Human diploid cell vaccine (HDCV):
Is recently used for immuno-prophylaxis without side-effects. This vaccine is prepared from rabies virus grown in human diploid cells.