Rabies

Rabies

Richa Chourasia

Lyssa virus induced fatal encephalomyelitis in most of the mammals is known as Rabies. Lyssavirus of the Rhabdovirus family is a bullet shaped RNA virus which is very fragile in nature. It is zoonotic in nature which can be prevented via vaccination. Rabies is present on all continents, except Antarctica. Rabies is one of the Neglected Tropical Diseases (NTD) that predominantly affects poor and vulnerable populations who live in remote rural locations. It occurs worldwide in mammals, with dogs, bats, and wild carnivores as the principle reservoirs.

In India, rabies is endemic in nature which causes approximate 25000-30000 deaths annually. The most common reservoir of rabies in domesticated areas is dogs and cats. While in wildlife wolves, foxes, coyotes, jackals, bobcats, lions, mongooses, skunks, badgers, bats and monkeys are the reservoir of the disease.

It can be transmitted through direct or indirect contact. Direct contact involves bite or scratches and contact of disrupted skin or mucous membrane with the infected saliva. Indirect contact includes inhalation of aerosolized rabies virus which is commonly found in infected bat caves that are infected with the virus.

Incubation period of rabies varies from 1 month to 1 year. Once clinical sign is developed, death is inevitable. All the animals shows signs of CNS disturbance, acute behavioural changes like sudden anorexia, signs of apprehension or nervousness, irritability, hyper excitability, ataxia, altered phonation, uncharacteristic aggressiveness and unexplained progressive paralysis. It has two forms:

Furious form– This is the classic “mad-dog syndrome.” There is rarely evidence of paralysis during this stage. The animal becomes irritable and, with the slightest provocation, may viciously and aggressively uses its teeth, claws, horns, or hooves. The posture and expression is one of alertness and anxiety, with pupils dilated. Noise may invite attack. Such animals lose caution and fear of people and other animals. Carnivores with the furious form of rabies frequently roam extensively, attacking other animals, including people, and any moving object. They commonly swallow foreign objects, eg, feces, straw, sticks, and stones. It is characterized by hyperactivity, excitable behaviour, hydrophobia, aerophobia and hyperaesthesia. Infected one dies usually in few days due to cardio-repiratory arrest.

Paralytic/ Dumb form– The paralytic form of rabies is manifest by ataxia and paralysis of the throat and masseter muscles, often with profuse salivation and the inability to swallow. Dropping of the lower jaw is common in dogs. The paralysis progresses rapidly to all parts of the body, and coma and death follow in a few hours.

Rabies in cattle and buffalo: Cattle with furious rabies can be dangerous, attacking and pursuing people and other animals. Lactation ceases abruptly in dairy cattle. The usual placid expression is replaced by one of alertness. The eyes and ears follow sounds and movement. A common clinical sign is a characteristic abnormal bellowing, which may continue intermittently until shortly before death. Whereas, in buffaloes dumb form of rabies is more common.

Rabies in Horses and mules frequently show evidence of distress and extreme agitation. These signs, especially when accompanied by rolling, may be interpreted as evidence of colic. As in other species, horses may bite or strike viciously and, because of their size and strength, become unmanageable in a few hours. People have been killed outright by such animals. These animals frequently have self-inflicted wounds.

Rabies is usually diagnosed with the help of clinical signs and symptoms. On post mortem examination brain tissue is preferred for the detection of virus in both animals and humans. In animals sample collection from live is avoided because of possible contamination whereas in human patients’ saliva, skin biopsy or hair follicle is collected for the detection. Gold standard test for diagnosis is Fluorescent antibody test (FAT) which works by the detection of viral antigen.

Diagnosis can be done either by direct microscopy or by demonstration of viral antigen. Under direct microscopy, intracytoplasmic Negri bodies (Inclusion body) can be seen in smears from brain. For staining such smears histological test like Seller’s Technique can be used. For the demonstration of viral antigen various tests like FAT, rapid rabies enzyme immunodiagnosis (RREID), direct rapid immunohistochemical test (dRIT), indirect rapid immunohistochistry test (IRIT), immunochromatographic techniques, ELISA etc. Other method of identification is animal inoculation (mouse) or cell culture inoculation from suspected samples but it requires highly specialized facility; and detection of viral RNA through RT-PCR.

Now what to do after exposure or bite from animals. Immediate treatment of a bite victim or animal is recommended after the exposure. Post exposure prophylaxis is warranted to prevent the entry of virus in the CNS through peripheral nerves. It includes:

Immediate washing of wound for 15 minutes with soap and water, detergent, povidine iodine or other substances that can kill the virus. According to WHO guidelines wound is divided into three categories and the prophylaxis varies according to them.

Do’s:

1. Observe the biting dog/ cat
2. Confirm the vaccine status of the animal
3. Bite by wild animals should be treated as category III wound
4. Bite from domestic rodent, squirrel, hare and rabbits, does not require treatment.
5. Everyone pregnant, lactating, infant old age and person with any concurrent illness must receive post bite vaccination.
6. Avoid suturing bite wound.
7. Do not put chili powder on the wound

Administration of post exposure vaccine and immunoglobulin:

Vaccination in humans: Pre exposure prophylaxis can be done by giving one full dose of vaccine intramuscular or 0.1 mL Intradermal on day 0, 7 and either on day 21 or 28. Post exposure vaccination done on day 0, 3, 7 and 28 after the bite either Intradermal or Intramuscular is recommended. (However switching between routes is not recommended) In case of category II and III wound immunoglobulins are injected around the wound. If Equine rabies immunoglobulins are used then it is given @ 40 IU per kg body weight of patient (commercial available in 300 IU/ mL concentration) and if human rabies immunoglobulins is to be used then it is given @20 IU per kg body weight (commercially available in the concentration of 150 IU per mL)

Vaccination in animals: For pre-exposure prophylaxis, vaccine is administered at the age of 3 months followed by booster dose after 1 or 3 years depending upon the type of vaccine used earlier. In healthy pre-vaccinated animal two dose of Intramuscular vaccine on day 0 and 3 is sufficient whereas in unvaccinated animal, vaccination given on day 0, 3, 7, 14 and 28 after the bite. If the animal is bitten by the rabid animal then the rabies immunoglobulins (Equine rabies immunoglobulins cab be give @ 40 IU/kg body weight with the maximum dose of 3000IU) are injected around the wound.

Equine Rabies immunoglobulins manufactured in India: (Pharmaceutical)

1. Central Research Institute, Kasauli, Himachal Pradesh
2. Bharat Serums and Vaccines, Limited, Mumbai
3. VINS Biopharma, Hyderabad.
4. Human Biologicals Institute, Hyderabad
5. Virchow Biotech Pvt Ltd, Qutubullapur, Telengana
6. Haffkine Biopharmaceutical Corp Ltd, Pimpri
7. Premium Serums & Vaccines Pvt Ltd, Pune
8. Serum Institute of India, Pune

Available Human rabies immunoglobulin in India:

https://www.who.int/news-room/fact-sheets/detail/rabies

https://www.pashudhanpraharee.com/control-and-elimination-of-rabies/

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