The Health Significance Of Prophylaxis Of Rabies Infection

Local treatment of bites, scratches and licks: Through cleaning of the wound by washing with soap and water repeatedly and then by 40 to 70% alcohol or 0.1% quarternary ammonium compounds (Cetavlon), eliminates the virus present superficially. Bite wounds should not be sutured straight away. In severe bites, local injection of antirabies serum of hyperimmune globulin helps in reducing the risk further.

Assessment of the risk: Animals incubating the disease may be apparently normal for five days before becoming symptomatic. Once they develop the disease, majority of them die within 5 days. Therefore the animal should be observed for 10 days, to decide on the need for vaccination. If the animal is obviously rabid or it is not traceable, vaccination is started straight away without any delay. If the risk is only class I or II, vaccination can be undertaken after observing the animal. In class III risk, vaccination is started, but if the animal is normal, it can be stopped. A rapid dog shows features like recent change in behaviour, aggressiveness, characteristic howl, tendency to bite objects indiscriminately, ataxia, paralysis and excessive salivation. Paralysis of bulbar muscles may be mistaken for impaction of foreign bodies in the throat.

The risk of developing infection can be estimated from the nature of initial injury.

Active immunization: This is achieved by antirabies vaccination (ARV). Vaccination affords considerable degree of protection, though, this is not absolute. Immunity is established after 10 to 14 days of starting the course and it lasts for 6 months. Antirabies vaccine was originally introduced by Louis Pasteur in 1885. At present, there types of vaccines are used.

Fixed virus vaccines: The fixed virus is grown in the spinal cord of sheep and it is inactivated by phenol (Semple) or beta propiolactone (BPL). The vaccine is usually injected subcutaneously on the anterior abdominal wall.

The major complications include local reaction at the site of injection and neuroparalytic accidents. Neurological complications occur with a frequency of 1/1000 vaccination. Due to this danger, ARV should be given only to persons in whome definite risk is proven or it is highly probable. Neurological complications of ARV are probably caused by allergic reactions to nervous tissue present in the vaccine. It is more common with those regimens when the total dose and duration are higher and when ARV is given repeatedly. Symptoms occur 1 to 2 weeks after starting ARV. The clinical picture may be that of encephalitis, encephalomyelitis, transverse myelitis, ascending paralysis or polyneuropathy resembling Guillain-Barre syndrome. In the spinal form, early involvement of the bladder is characteristic. The motor dysfunction may range from isolated cranial nerve palsy to severe and fatal ascending paralysis.

Complete rest at home and avoidance of alcohol during the course of vaccination may help in lowering the incidence of neurological complications. Neurological complications of ARV are managed as in the case of acute paralytic episodes. Corticosteroids and immunological process. Post-ARV encephalomyelitis is fatal in 5 to 10%. In those cases, who recover, prolonged morbidity occurs in 10 to 20%.

Attenuated Viral Vaccines: These are produced in chick (Flury) or duck embryos. Though, allergic reactions may occur, neuroparalytic accidents are much less common with this vaccine. The vaccines are used for active immunization of dogs and humans at risk of exposure.

Human diploid cell vaccine (HDCV): This is prepared by growing the fixed virus in human diploid cell strains (HDCS) W1-38 and inactivating it by beta-propiolactone or tri-n-butyl phosphate. This is more antigenic and the course of injection is shorter. There is no risk of neuroparalysis. At present, vaccines manufactured in France, Germany and USA are commercially available. Attempts are being made to manufacture this vaccine in developing regions like India for instance.

Passive immunization: Immediate protection is achieved by the administration of hyperimmune globulin or antirabic serum (ARS) produced from horses. ARS is a useful adjunct to vaccination if given within 5 days of the bite. The passive immunity persists for two weeks. The usual dose is 10 to 40 IU/Kg body weight. The possibility of serum reactions should be kept in mind when horse serum is used. ARS prepared in humans is also available. This is devoid of the hypersensitivity reactions caused by horse serum. The dose is 20IU/Kg body weight. Concurrent administration of ARS reduces the immunogenicity of the vaccine. Therefore booster doses of ARV are required at 10, 20 and 90^th day after the full course of ARV.

Personnel who have occupation risk of rabies, eg, veterinary surgeons, kennel trainers, etc can be actively immunized. Adequate protection is given by three injections of a potent vaccine at 5 to 7 days intervals followed by a booster, one month later. Protection lasts for up to three years. When an immunized person is exposed to the risk of rabies, he should receive booster doses of the vaccine- one dose for mild exposure and five daily doses for severe exposure, followed by a booster after 20 days (WHO 1966).