Case 65: Rabies Virus

Question 1

what are the characteristics of the rabies virus genome?

Answer 1

enveloped, helical, (-) sense ssRNA virus

Question 2

what is the clinical presentation of rabies?

Answer 2

• fever
• visual hallucinations
• malaise
• backpain
• muscle pains
• vomiting
• abdominal cramps

works as a roadside clean-up crew

Question 3

what would a PE of a rabies patient show?

Answer 3

• hyperesthesia = excessive physical sensitivity, especially of the skin
• increased agitation
• loss of orientation
• hydrophobia
• hypersalivation
• wide fluctuation in body temperature and BP

**agitation and hydrophobia are specific for rabies encephalitis

Question 4

what would a CBC of a rabies patient show?

Answer 4

everything is normal

Question 5

what is the shape of the rabies virus?

Answer 5

bulley-shaped nucleocapsid

Question 6

what are the two epidemiologic forms of rabies?

Answer 6

1. urban rabies = transmitted by dogs

2. sylvatic rabies = a disease of wild carnivores and bats

Question 7

what are the most common animal species that transmit rabies?

Answer 7

coyotes, foxes,
raccoons, and bats

cats and dogs are important as well, given the frequent contact with
people—especially in areas, such as developing countries, where vaccination is not
routine

Question 8

how is rabies transmitted?

Answer 8

1. it’s transmitted to humans by a bite or scratch from an infected animal with
   virus-laden saliva.
2. person-to-person transmission is also possible, via saliva or
   aerosolized froth from an infected person
3. on rare occasions, transplantation of infected
   tissues may cause disease

Question 9

what is the incubation period of rabies?

Answer 9

3-8 weeks on average

but it can be as short as 9 days or as long as 7 years depending on the severity of wound, site of wound,
and its distance from the brain

Question 10

what is the pathogenesis of rabies?

Answer 10

virus enters cells of the mucous membranes at the
bite site and within minutes multiplies locally

the virus buds from the cells but does not
lyse them

chronic infection is established when the progeny virus infects the sensory
neurons in the peripheral nervous system

viral glycoproteins bind to acetylcholine
receptors, contributing to neurovirulence of the rabies virus

the virus moves up
by axonal transport to the CNS and then multiplies in the CNS = there is no viremic
stage

once in the brain, the virus replicates exclusively within the gray matter

it then travels down the peripheral nerves to the salivary glands and other body
tissues, including lungs, kidney, and skin

secondary viral replication in mucinogenic
acinar cells of salivary glands facilitates secondary transmission via saliva

Question 11

what is the most characteristic pathologic finding of rabies in the CNS?

Answer 11

the formation of Negri bodies!

these are cytoplasmic inclusions found in neurons

Question 12

why does rabies cause encehalitis?

Answer 12

because rabies infects neurons in the brain

then virus-specific cytotoxic T cells, induced by
the viral glycoprotein, kill the virus-infected neurons, causing brain damage, and
encephalitis develops

the disease progresses to paralysis, and painful spasms of
swallowing muscles lead to avoidance (fear) of water (hydrophobia)

convulsions follow and the final stage is coma

Question 13

what causes death in rabies patients?

Answer 13

respiratory failure

Question 14

how do you prevent rabies?

Answer 14

1. individuals at high risk (e.g., veterinarians, park rangers, Peace Corps members) should
   receive pre-exposure immunization
2. human diploid cell rabies vaccine (HDCV), an
   inactivated vaccine prepared from virus grown in human diploid cell culture, is an
   approved vaccine
3. three-step postexposure prophylaxis is available for the exposed
   individuals and their contacts