RabiesRabiesLecture 6Lecture 6

Dr. Paul Bartlett, MPH., DVM., Ph.D.Dr. Paul Bartlett, MPH., DVM., Ph.D.

Transmission Transmission

The virus is typically transmitted by being The virus is typically transmitted by being deposited under the skin, usually through a bite deposited under the skin, usually through a bite wound.wound.

Contamination of a pre-existing wound is possible Contamination of a pre-existing wound is possible but unlikely because the local inflammatory but unlikely because the local inflammatory reaction which follows a wound, quickly seals the reaction which follows a wound, quickly seals the comprised skin and prevents entry of the virus.comprised skin and prevents entry of the virus.

Transmission across mucous membranes is also Transmission across mucous membranes is also possible, but less likely than a bite wound. possible, but less likely than a bite wound.

Aberrant Routes of TransmissionAberrant Routes of Transmission

A small number of human rabies cases have been A small number of human rabies cases have been reported following corneal transplants.reported following corneal transplants.– This suggests that human rabies cases may be This suggests that human rabies cases may be

underreported.underreported. Aerosol (airborne) transmission of the virus has Aerosol (airborne) transmission of the virus has

also been reported. However, this is possible only also been reported. However, this is possible only under unusual circumstances.under unusual circumstances.– Persons have contracted rabies presumably by airborne Persons have contracted rabies presumably by airborne

transmission after visiting bat caves (Frio Cave, Texas.)transmission after visiting bat caves (Frio Cave, Texas.)

Survivability of the Rabies VirusSurvivability of the Rabies Virus

The rabies virus is extremely short lived The rabies virus is extremely short lived under most environmental conditions.under most environmental conditions.– It is easily inactivated by heat and drying.It is easily inactivated by heat and drying.– Capable of surviving for a few days in cold Capable of surviving for a few days in cold

temperatures.temperatures. Thorough and immediate washing of bite Thorough and immediate washing of bite

wounds with plenty of soap and water is wounds with plenty of soap and water is the best preventative treatment for rabiesthe best preventative treatment for rabies

Course of a Rabies InfectionCourse of a Rabies Infection

Once introduced, the rabies virus travels Once introduced, the rabies virus travels retrograde up the nerves to the spinal cord - retrograde up the nerves to the spinal cord - eventually reaching the brain.eventually reaching the brain.

From the brain, the virus spreads to the From the brain, the virus spreads to the salivary glands.salivary glands.

The incubation period is usually 6 to 8 The incubation period is usually 6 to 8 weeks in humans but it may be longer.weeks in humans but it may be longer.

Viral Spreading in AnimalsViral Spreading in Animals In cats and dogs, the clinical symptoms usually In cats and dogs, the clinical symptoms usually

begin before the virus is found in the saliva.begin before the virus is found in the saliva.– Sometimes virus can be found one to three days before Sometimes virus can be found one to three days before

clinical symptoms in cats and three to five days in dogs. clinical symptoms in cats and three to five days in dogs. Ferrets is something < 10 days. Ferrets is something < 10 days.

No reliable information regarding the appearance of No reliable information regarding the appearance of virus in the saliva is available for other animal virus in the saliva is available for other animal species .species .– There is some evidence that certain wildlife species, like There is some evidence that certain wildlife species, like

skunks and bats, may excrete virus in their saliva for long skunks and bats, may excrete virus in their saliva for long periods before becoming ill.periods before becoming ill.

Terrestrial Reservoirs of Rabies Terrestrial Reservoirs of Rabies Different terrestrial (non-bat) mammalian species Different terrestrial (non-bat) mammalian species

are the rabies reservoirs in different parts of the are the rabies reservoirs in different parts of the country.country.– Strains in the USA include - skunk, raccoon, fox, and Strains in the USA include - skunk, raccoon, fox, and

coyote.coyote.– For a given strain, only transmission within the host For a given strain, only transmission within the host

species is sufficiently successful to maintain the disease species is sufficiently successful to maintain the disease from year to year.from year to year.

This was observed before monoclonal antibody This was observed before monoclonal antibody testing revealed that distinctly different strains of testing revealed that distinctly different strains of the virus were involved.the virus were involved.

Have virus: CNS fluid, saliva, nervous tissue

Don’t have virus: milk, urine, feces, muscle

Dumb Rabies?

Furious Rabies?

Cases of Animal 1955-2000Rabies,Total Dom estic Wild

Rabies in W ild Animals, 1955-2000

Rabies in W ild Anim als by M onth, 2000

SkunkRaccoon

Coyote

Skunk

Distribution of M ajor Terrestrial Reservoirsof Rabies in the United States

Fox

Skunk

Fox

Fox

Skunks, 2000

N=2223

1 Case 15 Cases 30 Cases

Changes from 1999 to 2000Increase Decrease

1 CASE

15 CASES

30 CASES