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Symptoms, Mode of Transmission, Prophylaxis and Control Rabies

RABIES VIRUS

Morphology

1: Bullet-shaped when seen by electron microscope, size — 76 x 175 nm .2. Nucleocapsid shows helical symmetry and contains a single-stranded unsegmented RNA genome and a viral transcriptase. 3. Outer lipoprotein envelope contains protruding haemagglutinating peplomer spikes, 10 nm long.

Rabies is a natural infection of dogs, foxes, wolves, skunks, cats and bats. Fox, vampire bats and dogs are important maintenance hosts. In fected bats are constantly viraemic but are usually asymptomatic. Man is most frequently infected by bites of dogs, but cats and other animals may be responsible. Saliva containing viruses is deposited in the wound. If the area is not cleaned and cauterized, rabies develops in about half of such cases. Infection may also be acquired from aerosols of virus or contaminated dust of an area housing infected bats. Incubation period varies from 1-3 months, sometimes may be short (10 days) particularly in children and with wounds on face and neck. The

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virus probably multiplies in nerves and muscles locally and spreads along peripheral nerves and ascends to CNS (spinal cord and brain). It multiplies in brain and causes encephalitis. The virus spreads widely from brain along the nerve trunks to salivary glands and other tissues.

Symptoms

Prodromal Phase:The non specific prodromal phase symptoms include fever,

malaise ,headache,photophobia,nausea and vomiting, sore throat and fever lasting 2-10 days.

Acute Neurologic Phase: Encephalitic (furious ) phase 80% and Paralytic phase -20%

Encephalitic rabies

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After a prodromal period of headache malaise and low grade fever and anxiety of 1-10 days, infected person develops characteristic fear of water (hydrophobia, alternative name for rabies). Though patient is thirsty, attempts at drinking provoke violent contraction of diaphragm and respiratory muscles. Thereafter, mere site or sound of water precipitates distressing muscular spasm. Death usually occurs within week of onset of symptoms. Prognosis is almost always fatal.

Paralytic rabies:

The characteristic features of paralytic rabies are early and prominent muscle weakness,often starting in the bitten extremity that spreads to produce quadriparesis and facial weakness. The course of disease is slower, infected patients rarely recover and survive. Death usually results from respiratory arrest or other complications.

Transmission

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Rabies is a natural infection of dogs, foxes, wolves, skunks, cats and bats. Fox, vampire bats and dogs are important maintenance hosts. In fected bats are constantly viraemic but are usually asymptomatic. Man is most frequently infected by bites of dogs, but cats and other animals may be responsible. Saliva containing viruses is deposited in the wound. If the area is not cleaned and cauterized, rabies develops in about half of such cases. Infection may also be acquired from aerosols of virus or contaminated dust of an area housing infected bats. Incubation period varies from 1-3 months, sometimes may be short (10 days) particularly in children and with wounds on face and neck. The virus probably multiplies in nerves and muscles locally and spreads along peripheral nerves and ascends to CNS (spinal cord and brain). It multiplies in brain and causes encephalitis. The virus spreads widely from brain along the nerve trunks to salivary glands and other tissues.

Prophylaxis and Control A. Pre-exposure prophylaxis: It is necessary for persons who handle potentially infected animals. Two intradermally injections of 0.1 ml. of human diploid cell strain vaccine are given at 4 weeks interval. This is followed by yearly boosters. B. Post exposure prophylaxis: The wound is thoroughly cleansed first with water and soap and then with quaternary ammonium detergent (Cetavlon) or tincture iodine or alcohol. Damaged tissue excised and wound is left unsutured. Rabies can be prevented if treatment is initiated in a day or two of biting. The biting animal should be kept in strict isolation, if possible, for 10 days. If it remains healthy after 10 days, rabies may be excluded. When the risk of rabies is great, individuals should be given post-exposure prophylaxis by hyperimmune serum and vaccine.Vaccine Paesteur first (1885) developed attenuated rabies vaccine by drying spinal cords of infected animals. Vaccines are of two categories — neural and non- neural . Because of some risks with neural vaccine, nonneural vaccines are being used increasingly.

Neural Vaccine-made from nervous tissue of sheep,goat or mouse ,infected with the fixed rabies virus.

Eg:The Semple Vaccine and Beta propiolactone (BPL) vaccine.

Non Neural Vaccines:

i) Human Diploid Cell Vaccine ( HDCV)ii) Ii)Rabies Vaccine,Adsorbed ( RVA)iii) Purified chick embryo cell vaccine ( PCEC) iv) Duck Embryo Vaccinev) Live Attenuated Virusesvi) Live recombinant vaacinia virus vaccine.

Prevention and Control

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Pre –exposure prophylaxis: Vaccination before exposure to infection.

Post exposure prophylaxis : All bite wounds and scratches should be washed thoroughly first with water and soap and then with quaternary ammonium detergent or tincture of iodine or alcohol. Damaged tissue is excised and wound is infiltrated by rabies antiserum or antirabic ointment. Tetanus prophylaxis is given and antibiotic administered. The wound is left unsutured.

An unvaccinated peson shold be immunized with rabies immunoglobulin( RIG).

All biting animals should be kept in isolation , if possible, for 10 days.

Vaccines for animals- animals should be vaccinated to prevent accidental transmission of rabies

Control measures include vaccination of household dogs by a Flury (Live) canine vaccine, destruction of spray dogs and control measures on wild life.

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