Background

Rabies is a zoonotic viral disease of mammals belonging to the genus Lyssavirus of the family Rhabdoviridae, causing fatal encephalitis in mammals. Rabies virus is transmitted by the bite of a rabid animal. In African and Asian countries, domestic dogs are the reservoir of the rabies virus. The bite of a rabid dog causes more than 99% of the cases. The incubation period of the rabies virus is highly variable, ranging from days to years and on an average of 2-3 months depending on the location and depth of the wound, the concentration of virus particles, and virus strain. Louis Pasteur, in 1885 developed the first vaccine against rabies. Rabies generally remains ignored in humans and animal, in the poor and marginalized population where it is often endemic. There is no organized surveillance system as rabies is not a notifiable disease either for human or animal cases. Rabies causes a significant impact on the health and economy of the human and animal populations. Canine rabies causes approximately 3.7 million disability-adjusted life years globally. Most of the human and animal bite cases in India are due to stray dogs, which are reservoir hosts of rabies and responsible for >97% human deaths due to rabies. The poor management of dog population and low standards of dog care are the main factors responsible for the high endemicity of canine rabies in India. The eradication of canine rabies in stray dogs is the main target for the control of rabies in India. Public veterinary services, in collaboration with local municipalities, provide the veterinary immunization; some private veterinary services on a limited scale also provide vaccination. For the removal of stray dogs, municipalities are responsible for different cities. At specialized prevention facilities known as prophylaxis centers, post-exposure vaccination and rabies immunoglobulin are given to infected humans or animals, which are present throughout the country. The prophylactic inactivated rabies vaccines are produced in cell cultures according to the WHO protocol. All the victims of animal bites are referred to these centers, where they are given five doses of the vaccine and rabies immunoglobulin. Actions on the animals are according to the national and international procedures. The owners are asked to quarantine the biting animals for ten days. If an animal develops any symptoms of rabies, then they are asked to visit the prophylaxis centers. All the procedures must be strictly followed to control and eradicate rabies.

Cause

A virus disease caused by Lyssavirus of family Rhabdoviridae

Host Species

All warm-blooded animals.

The disease occurs in cattle, buffalo, goat, sheep, pigs, horses, dogs, cats and wild animals.

• The rabies infected animals are the main source of infection.
• The bite of an infected animal is one of the possible route of spread of rabies.
• The contamination of skin wounds by fresh saliva carrying rabies virus may result in infection.
• The virus may appear in the milk of affected animals, however transmission by this means is unlikely as infection.
• When infected insectivorous bats reside in high population in a cave, inhalation acts as a route of infection.
• The native fauna, including foxes, skunks, wolves, coyotes, vampire, insectivorous and fruit-eating bats, raccoons, mongoose, and squirrels provide the major source of infection in some countries where domestic carnivora are well controlled.
• Domestic livestock like cattle are generally considered as dead end host but occasional transmission to humans may occur if the mouth of a rabid animal is manipulated during treatment or examination.
• Rabies also occurs in swine herds where the skunk population is high.

Cattle

Time requirement from infection to manifestation of clinical signs varies from 2 weeks to several months in most species. But this depends upon the site of bite by rabid animals.

Unvaccinated cattle may experience shorter incubation and clinical duration of disease than vaccinated cattle.

The clinical signs are observed in two-forms:

Furious form

• This form is seen in more than 70 % cases.
• Major clinical findings are excessive salivation, behavioral changes including muzzle tremors, vocalization, loud roaring (bellowing), aggression, hyperesthesia and/or hyperexcitability and pharyngeal paralysis.
• The sound is characteristically hoarse and is exaggerated.
• Sexual excitement of bulls is common, bulls often attemp to mount inanimate objects. Multiple collections of semen for artificial insemination can be possible during very short periods from rabies infected bulls.
• Paralytic forms
• Knuckling of the hind fetlocks, sagging and swaying of the hindquarters while walking.
• Flaccidity of the tail to one side is considered as one of the early signs.
• Low degree of sensation as well as weakness of hindquarters is common.
• Tenesmus, with paralysis of lower jow, resulting in the sucking in and blowing out of air, usually occurs late in the incoordination stages just before the animal becomes recumbent.
• Drooling of saliva is one of the most constant findings.
• The yawning movements are more accurately described as voiceless attempts to bellow.
• The animal becomes recumbent and unable to rise after development of paralysis.
• Some animals do not eat or drink, although they may take food into the mouth.
• There is apparent inability to swallow. Others eat normally until the terminal stages.
• The course may vary from 1 to 6 days.
• Bulls in this stage often have paralysis of the penis.
• Death usually occurs 48 hours after recumbency and after a total course of 6-7 days.
• However, the clinical signs vary widely and all the classical clinical signs may not be observed in each rabies infected animals.

Sheep and Goat

• In sheep & goat, rabies is generally seen in large numbers because rabid dog / fox attacks / bites group of these animals.
• Clinical signs are more or less similar to that of cattle.
• Some animals show sexual excitement, attack humans or each other, and vigorous wool pulling, sudden falling after violent exertion, muscle tremor, and salivation are characteristic.
• Most sheep remain quiet and anorectic.
• Goats are commonly aggressive, and continuous bleating/crying is common.

Pigs

• Pigs show dullness, incoordination, excitement and a tendency to attack
• Affected sows show twitching of the nose, rapid chewing movements, excessive salivation, and clonic convulsions.
• Infected pigs walk backward.
• Later, paralysis & eventually, death occurs 12-48 hours after the onset of signs.
• The clinical findings in pigs are extremely variable; only one or two of the classical findings are seen in individual cases.

Horses

• Mostly, there is lack of nervous signs but symptoms are similar to paralytic form of the disease.
• Muzzle tremors are the most frequently observed and most common initial signs.
• Initially, there will be abnormal postures, frequent whinnying, unexplained aggressiveness and kicking, biting and colic.
• Sudden onset of lameness is observed in one limb followed by recumbence on the next day.
• High-stepping gait, ataxia, apparent blindness, and violent head- tossing are also seen.
• Lameness or weakness in one leg may be the first sign observed, but the usual pattern of development of signs starts with lassitude, then passes to sternal and lateral recumbency, followed by paddling convulsions and terminal paralysis.

Management

• Bite area should immediately be washed with alkaline solution preferably 20% soap solution.
• Antibiotic therapy coverage may be required preventing infection in bite wound. Post-bite vaccination should be started immediately.
• The person handling the rabies infected animal should wash hands with soap solution properly.

Control

• Anti-rabies vaccination of dogs and cats is the only effective way to control the disease.
• The spread of virus can be prevented by controlling access of wildlife species which are likely to come into contact with the farm livestock.

Type of vaccines

Inactivated cell culture vaccine (Aluminium hydroxide gel adjuvanted)

Vaccination schedule

Two types of vaccination schedule are followed

Pre-bite vaccination (1 dose S/C route)

First vaccination is done at 3-4 months of age and followed by booster dose after 21 days of first vaccination, thereafter annual vaccination is required.

Post-bite vaccination (1 dose S/C route)

Post bite vaccination is recommended at 0, 3rd, 7th, 14th, 28th and 90th day of bite of animals

Source/manufacturer of vaccine in India

Virbac Animal Health India Pvt. Ltd., Mumbai, Maharashtra

MSD Animal Health, Intervet India Pvt. Ltd., Pune, Maharashtra

Intas Animal Health, Ahmedabad, Gujarat

Indian Immunologicals, Hyderabad

Zoetis India Ltd., Mumbai, Maharashtra