RABIES

BY

M.N.O. UWAMOSE

SEPTEMBER, 2014

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ABSTRACT

Rabies is an acute viral infection of the nervous system caused by a virus.

The virus is commonly transmitted to man through the bite of a rabid animal.

More than 3.3 billon people are at risk of rabies worldwide, with

approximately 55,000 deaths estimated per year. The incidence of Rabies

infection per year in the world is estimated at 3.3 billion to 3.6 billion with

approximately 1.74 million deaths. Rabies epidermis occurs in Asia, North and

South America, and Africa. Rabies virus is a member of the Rhabdoviridae

family (Genus: Lyssavirus). The virus travels to the brain through the

peripheral nerves causing acute encephalitis (inflammation of the brain) in

warm-blooded animals (man). Early symptoms associated with rabies

includes Malaise, headache and fever, progressing to acute pain, restlessness,

hyperactivity, uncontrolled excitement, depression, hydrophobia, etc. Rabies

can be diagnosed by isolating the virus from the patient’s saliva, throat,

corneal impression or skin. Treatment is often by injection of rabies vaccines,

antiserum, and immunoglobin. Generally, Rabies is a neglected disease of the

poor and vulnerable populations. It occurs mainly in rural communities where

measures to prevent dog to human transmission have not been implemented

and deaths are rarely reported. Educating people about the severity of the

disease and also focus on the animal reservoir will help to control the disease.

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1.0 INTRODUCTION

Rabies is an acute viral infection of the nervous system that

primarily affects dogs and can also be transmitted to

humans. It is a zoonotic infectious disease caused by a virus.

The word Rabies originated about 3000BC from the word

Rabha, which means, “violence” (Adedeji et al., 2010). It

was once known as HYDROPHOBIA. Rabies virus is a

member of the Rhabdoviridae family (Genus: Lyssavirus).

The virus is found in the salivary glands and central nervous

systems of infected warm-blooded animals (including man)

from where it travels to the brain through peripheral nerves.

This deadly viral infection causes acute encephalitis

(inflammation of the brain) in warm-blooded animals. Once

symptoms develop, rabies is usually very fatal.

The incidence of Rabies occurs worldwide with an estimated

of 3.3 billion to 3.6 billion individuals at risk of the infection

and approximately 1.74 million deaths. An estimated number

of 55,000 people die each year from Rabies, 99% of which

are from rabid dog bites. 99% of human deaths due to rabies

occurred in Asia and Africa with an estimated 31,000 and

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24,000 deaths respectively. Rabies epidermis occurs in Asia,

North and South America, and Africa. In 2005, more than 12

million individuals received a Post Exposure Prophylaxis

(PEP) treatment against rabies, this treatment consist of the

administration of rabies immunoglobulin. This prevented an

estimated death of about 280,000 people (WHO 2005).

NIGERIA STATISTICS

Rabies was first reported in Nigeria in 1912 in two persons

but the first laboratory confirmation was in 1925 by

demonstration of Negri bodies in the brain smear of a mad

dog (Ekele, et al., 1984). The disease has been declared

endemic in Nigeria and it remains one of the most important

zoonoses in the country (Nawathe, 1980; Kujul, et al.,

2010).

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2.0 PROPERTIES OF THE RABIES VIRUS

Rabies is caused by a neurotropic virus of the genus

Lyssavirus, family Rhabdoviridae. The virus is a single

stranded, neurotropic, negative sense RNA virus whose

genome encodes five proteins: a Glycoprotein, a

Nucleoprotein and three other proteins – Matrix Protein,

Phosphoprotein and Polymerase.

The virus is bullet shaped and has a protein coat with a lipid

envelope. The outer surface of the virus is covered with

thumb-like glycoprotein projections that are 5-10 nm long

and 3 nm in diameter. The virus length averages

approximately 780 nm. (Albertini et al., 2006).

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3.0 TRANSMISSION

Rabies virus is zoonotic, meaning it can be transmitted from

one species to another such as from dogs to humans. Dogs

are the main host and transmitter of rabies (Suzuki K, et al.,

2008). They are the source of the infection in all of the

estimated 55,000 human rabies deaths annually in Asia and

Africa. Other sources of the infection include bats, deer,

e.t.c.

Rabies is transmitted through the bite or scratch of infected

animal (Rabid animal) which introduces the virus through the

skin. Bites cause approximately 99% of Rabies cases

worldwide (Awoyomi et al., 2007).

Transmission can also occur when infectious materials

(saliva) come in direct contact with human fresh skin

wounds, and also by kissing.

Human – human transmission of rabies is possible through

tissue (such as corneas) transplants from infected humans.

Rarely, rabies may be contracted by inhalation of virus

containing aerosol (Takayama 2005).

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4.0 PARTHENOGENESIS

Rabies infects the brain and spinal cord in the body. Rabies

infection is initiated in the victim on acquisition of the virus

through the bite or direct saliva contact with infected animal.

The virus then incubates at the site of inoculation replicating

within muscle cells. After long incubation period, the virus

enters the peripheral nerves and travels by retrograde

axonal flow toward the Central Nervous System, first to the

spinal cord then to the brain. Once in the brain, the virus

travels by axonal flow down the trigemmal nerve to the

salivary glands. The virus is found in the saliva and the

animal becomes infective 3 – 5 days depending on the onset

of clinical signs. The length of time of development of clinical

signs is related to the distance the virus must travel (Drew

2004; Beard 2001; Takayama 2005).

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5.0 SYMPTOMS

The period between infection and the first flu-like symptoms

is 2 – 12 weeks. This is called the incubation period.

Early symptoms of the disease include malaise, headache

and fever, progressing to acute pain, restlessness,

depression, and hydrophobia. Finally, the patients may

develop convulsions, muscles paralysis starting at the site of

the bite or scratch, and experiences periods of mania and

lethargy. Eventually, a coma slowly develops. Death occurs

due to respiratory insufficiency 10–14 days after the onset of

symptoms (Awoyomi et al., 2007).

As the virus spreads through the central nervous system,

progressive fatal inflammation of the brain and spinal cord

develops. Two forms of the disease can follow (Takayama

2005):

1. The furious or mad form

2. The dumb or paralytic form.

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People with furious rabies show uncontrolled behavior,

hyperactivity, hydrophobia, and sometimes aerophobia. After

a few days, death occurs by cardio-respiratory arrest.

The dumb form is a more advanced stage of the furious type.

People with this form of rabies usually have their muscles

gradually become paralyzed, starting at the site of the bite or

scratch, a coma slowly develops and eventually death

occurs.

Furious rabies symptoms result from changes to the limbic

system, and the dumb form results from changes to

neocortex. Other signs such as excitement, salivation and

increased sexual activity result from the effects on the

autonomic nervous system (Drew 2004).

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6.0 EFFECTS OF RABIES

Rabies disease is known to affect the spinal cord and the

brain. This infection travels to the spinal cord and then to the

brain through the peripheral nerves. Undiagnosed, delayed

or untreated rabies causes acute encephalitis (inflammation

of the brain), damage to the nervous system, muscles

paralysis, and death (Drew 2004).

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7.0 DIAGNOSIS OF RABIES

Rabies can be diagnosed in several ways such as laboratory

test that isolate the virus from the patient’s saliva or throat

or corneal impression, skin biopsies and post-mortem tissue

samples by Fluorescent Antibody Test (FAT) or by the Avidin-

Biotin technique.

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8.0 TREATMENT OF RABIES

Treatment is by means of Intradermal injections of rabies

vaccines, Antiserum and Immunoglobulin which may prevent

the virus from infecting if given within two (2) days. The

required vaccines for the treatment of rabies according to

World Health Organization (WHO) include;

Human Diploid Cell Vaccine (HDCV): Rabivac™;

Purified Vero Cell Vaccine (PVRV): Verorab, Imovax,

Rabies vero, TRC Verorab™;

Purified Chicken Embryo Cell Vaccine (PCECV):

Rabipur™.

The incubation period for rabies enables effective treatment

to be given, but if symptoms appear, they are treated with

sedative drugs and analgesic drugs (Jackson 2008; Suzuki et

al., 2008).

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9.0 PREVENTION AND CONTROL

Preventive and control measures include:

Immunization of all dogs and cats owned by an

individual or by the community,

Immunization of persons with proven or probable

exposure to rabies and administer rabies

immunoglobulin in case of severe exposure (WHO

2005),

Vaccination and elimination of stray dogs should be

enforced.

Wild animals should not be kept as pets,

Killing of wildlife around during an epidemic,

Humans at high risk (e.g. laboratory personnel,

professions at high risk) must receive pre-exposure

immunization,

People living or travelling to countries where rabies is

endemic should be vaccinated with three doses of

human diploid cell rabies vaccine (Adedeji et al.,

2010),

Strict quarantine regulations,

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Lastly, oral vaccines should be given to wild animals

through bait. (WHO, 1997)

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10.0 CONCLUSION

Rabies is a neglected disease of the poor and vulnerable

populations whose deaths are rarely reported. It occurs

mainly in rural communities where measure to prevent dog

to human transmission have not been implemented.

Eradication of rabies should be geared towards prevention,

control and treatment. This could be achieved through health

education, improvement of quarantine regulation and human

and animal vaccination. It can be wiped out across the world

if sufficient vaccinations are carried out on domestic dogs. If

prompt medical care is available, rabies is uncommon in

human beings but remains one of the most feared diseases.

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