RABIES: A DREADFUL DISEASE Pashu Sandesh

RABIES: A DREADFUL DISEASE

Pashu Sandesh, 03 April 2019

Dr. Brajesh Kumar¹, Dr. Deepikesh Joshi², Dr. Vipin Chandra³ and Dr. K Puhle Japheth⁴

Definition

Rabies is a viral disease of animal mainly affecting carnivores like dogs, wolves, foxes caused by Lyssavirus and characterized by encephalitis and presence of intra cytoplasmic inclusions in nerve cells.

Etiology

Lyssa virus (Bullet shaped RNA virus) of Rhabdoviridae family

Incidence

Rabies is a major zoonotic disease, which remains a serious public health problem in the world. Rabies has been recorded in various parts of the world. In Asia, Africa, Latin America and the middle east, rabies is endemic while Australia, New Zealand, Hong Kong, Singapore, Britain, and Hawaii are free from Rabies.

Susceptible Host

Extremely susceptible: Dog, fox, wolf, jackal, cat, mongoose, bat.

Moderately susceptible: Cattle, goat, sheep, horses,

Cattle and equine are dead end host. Vampire bats act as vectors for the virus.

Incubation period

Depends on the site of bite. “Nearer the bite to the head, shorter the incubation period”. It may vary from 2 weeks to one year.

Mode of Transmission

Through bite of an infected animal
Since the virus is present in the saliva, infection by flies is facilitated
Licking of the wound by the rabid dog may also result in infection
Haematogenous spread
Infection may spread to the foetus in-utero from an affected bitch

Pathogenesis

After the bite, virus is deposited in the wound through a break in the skin. Local replication of virus in epithelial cells and myocytes takes place.
Virus enters into nervous system at motor end plate and binds to receptors for acetylcholine.
Then, the virus spreads within nerve cells. Virus multiplication occurs in the spinal cord and brain stem, cerebral cortex and hippocampus
Virus has got great affinity for the salivary glands due to which virus spreads along the nerves that innervate the salivary glands i.e. the facial and glossopharyngeal nerves, and from there, it is excreted through saliva.
Centrifugal spread takes place through nerves to salivary glands, cornea and tonsils. Virus replicates rapidly in salivary gland
Irritation induced by virus in the nerves cells causes furious form
In CNS: Virus damages the nerve cells and vascular endothelium

Clinical forms

Furious form /Excited: Animal goes into rage ( violent anger), indiscriminate biting, barking at imaginary objects, chews inanimate objects, red eye – Vacant look is seen, champing of jaws, dribbling of saliva, change of voice is observed. In Goats, signs of Rabies include barking like a dog.

Dumb form (Paralytic form): Sick, sluggish, progressive weakness, vacant look, does not obey orders, does not recognise family members, try to hide in corners. Death takes place in 3 to 4 days after the onset of symptoms at least within 10 days.

In Horses, Rabies virus causes Colic while in Cattle, excessive Bellowing is observed. In Cats , no dumb form is found while in Rabbit, only dumb form is found. Bulls and rams may show increased sexual libido as a symptom of Rabies.

Gross lesions

Limited only to CNS
Hyperaemia, oedema with petechiae on meninges
In other animals, lesions of bite on skin must be present

Microscopic lesions

Perivascular cuffing by lymphocytes in brain particularly hippocampous.
Microglial cell, plasma cells and lymphocytes proliferation and form small nodules – "BABES NODULES ". Satellitosis around ganglion cells is seen.
Degeneration of ganglion cells – Neuronophagia seen in hippocampus and brain stem. Similar changes in cerebrospinal and sympathetic ganglia.
Negri bodies: These are intracytoplasmic inclusion bodies found in neurones. They can be seen in the impression smear of Hippocampus.
In Cattle, Purkinje cells of cerebellum are found in the impression smear. Aggregate of viruses are also seen as round/oval/acidophilic (magenta red) with basophilic granules.

Diagnosis

Diagnosis is done using the following methods:

History of bite is investigated.
Diagnosis is generally based on symptoms and lesions
Immunodiagnostic test: Fluorescent Antibody Test (FAT) and Enzyme Linked Immuno Sorbent Assay (ELISA)
Observation of the animal culprit of the bite for 10 days (if the animal is dead within 10 days, then the bitten animal has a major chance to be affected by Rabies virus)
Impression smear of Hippocampus stained by seller stain should be observed for Negri bodies.
Mouse inoculation Test: On the 5th, 6th and 7th days one mouse is sacrificed and the brain is examined for Negri bodies. Negri bodies is usually seen on the 5^th and 6th days.
A biological test, injecting the brain tissue into rabbits intra-cranially can also done for conformation
Corneal or saliva test
Immuno-peroxidase Test (IPT)
Complement Fixation test (CFT)

Treatment

Proper treatment can prevent the disease within 10 days of exposure, if the treatment is given properly. Bite-wound should be thoroughly washed for five minutes using an antiseptic soap to reduce virus particles. Then, povidone-iodine must be applied on the wound which further reduces the number of virus particles.

The first dose of rabies vaccine is administered on the day of exposure along with additional doses on 3^rd, 7^th, 14^th, 28^th and 90^th days post bite. Animals who have received pre-bite vaccinations don’t receive the complete course of post-bite vaccination but only on the day of exposure and the 3^rd day.

A three to seven day course of Amoxicillin/ clavulanate (Augmentin) is generally considered as the first-line prophylactic antibiotic treatment for the bites. Tetanus vaccination is recommended after an animal bite.

Prevention and control:

The following steps can be followed as the measures of prevention:

Vaccinating the animals with pre-bite Rabies vaccination.
Keeping the pets under supervision
Contacting an animal control officer or animal behaviour expert especially when animal is acting strangely
Spreading awareness regarding the disease through various camps and awareness programmes
Maintaining the population of stray dogs through animal birth control programmes

Hence, it is evident that Rabies causes a major threat to all the livestock and other pet animals around the world due to its high incidence. Animal/ livestock owners must attempt to their full force to learn the preventive measures to protect their animals from the disease. Proper treatment of the animals exposed to the virus must be done to prevent any loss of life. The aforementioned points of control and treatment must be kept in mind so that the effects of this dangerous disease are minimised or eliminated.

Dr. Brajesh Kumar¹, Dr. Deepikesh Joshi², Dr. Vipin Chandra³ and Dr. K Puhle Japheth⁴

¹Assistant Professor, Department of Veterinary Pathology, Apollo College of Veterinary Medicine, Jaipur (Rajasthan)

²Assistant Professor, Department of Livestock Production Management, International Institute of Veterinary Education and Research, Rohtak (Haryana)

³Research Scholar, Department of Livestock Production Management, Post Graduate Institute of Veterinary Education and Research, Jaipur (Rajasthan)

⁴Assistant Professor, Department of Livestock Production Management, International Institute of Veterinary Education and Research, Rohtak (Haryana)