Structure

Transmission

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment

Family: lyassavirus of rhabdovirus

Genome: single-strand RNA, -ve polarity

Size: 130-240nm

Helical nucleocapsid

Bullet-shaped, enveloped particle with spike projections.

Rabies infects dogs, cats, bats and foxes.

Dogs are the main danger to humans:

- virus is present in saliva of infected dogs for up to 7 days.

Aerosol infection:

- laboratory accident

- bat-infested caves

Corneal transplants

Virus multiplies locally at bit site and then infects sensory neurons.

Moves by axonal transport to CNS.

Multiplies in CNS and then travels down peripheral nerves to salivary glands and other organs.

From salivary glands, it enters the saliva to be transmitted by bite.

No viraemic stage.

Almost fatal encephalitis in brain with death of neurons and demyelination.

Infected neurons has eosinophilic cytoplasmic inclusion called a Negri body.

Incubation period: varies according to location of bite, from 2 to 16 weeks; shorter when bite is on head than on leg.

Prodromal phase:

- fever, anorexia.

- pain & paraesthesias in area of bit.

- irritability, apprehension.

- hydrophobia due to spasms of respiratory muscles.

Excitation phase:

- hyperventilation, hyperactivity

- disorientation, seizure.

Paralytic phase:

- lethargy

- paralysis of somatic muscles, bladder and bowels.

- gradual involvement of cardiac muscles and paralysis of respiratory muscles lead to death.

Prognosis: disease is virtually always fatal.

Isolation:

- saliva

- skin

- eyes, brain

Antigen detection:

- corneal impressions or neck skin biopsy.

- Direct Fluorescent Antibody test.

Histologic staining of Negri bodies in the cytoplasm of hippocampal neurons.

Preexposure prevention:

- preexposure immunization with rabies vaccine given to people in high-risk groups, vets, zookeepers.

Postexposure prevention:

- given after exposure to virus.

- long incubation period of disease allows virus in vaccine sufficient time to induce protective immunity.

- involves use of both vaccine and human rabies immune globulin – passive-active immunization.

- wound cleaning with soap and water.

Human diploid cell vaccine:

- contains inactivated virus

- prepared in human diploid embryo lung cells.

- administer intramuscularly or subcutaneously into deltoid in 5 doses spread at 0, 3, 7, 14 and 30 days.

Live attenuated virus grown in chick embryos used for immunization of dogs & cats