Lecture 56 & 57 Viral Infections of CNS

Question 1

Origin of name Arbovirus

Answer 1

Arbovirus means arthropod borne virus

This is because the common vector for these viruses are mosquitos and ticks

Question 2

Common host of arboviruses

Answer 2

Birds and small mammals are common hosts

Humans are dead end hosts

Question 3

Outcome of arbovirus infection depends on what?

Answer 3

Specific infective agent
Age of patient
Degree of encephalitis

Question 4

Clinical manifestations of arboviruses

Answer 4

Most cases are subclinical and undiagnosed, most never know they had a CNS infection

Severe cases involve: fever, headache, vertigo, photophobia, nausea, vomiting, confusion, personality changes, seizures

Recovery can be complete, or there can be permanent sequelae. Kids are especially at risk–deafness, psychomotor and learning difficulties

Question 5

Arbovirus diagnosis and ID

Answer 5

• Very difficult to diagnose, season may help, outbreaks will also help
• ID: is done by IgM antibody capture ELISA (MAC-ELISA) on CSF or serum, CSF is better indication of what is happening in CNS
• Viral culture is not common with arboviruses
• Indirect Fluorescent Antibody Test works for Colorado Tick Fever and some arboviruses
• Nucleic acid-based tests like RT-PCR can be useful and meaningful if a pos result is obtained, but is usually unreliable for acute diagnosis

Question 6

Describe host, vector, vector amplification, and epidemic relationship

Answer 6

Hosts like birds become reservoirs when they have high levels of viremia without showing symptoms. As reservoirs, they pass the virus on to arthropods that bite them and cause an increase in vectors in the environment. The more vectors, the more likely humans are to be infected=> epidemics. So, when mosquitos are active, the diseases are present and active.

Question 7

How to control arbovirus infections

Answer 7

Arboviruses have a natural cycle in nature among birds and mammals. This makes complete eradication of the viruses impossible. The best way to control is through:

1) Vector control
2) Avoiding exposure
3) Immunize non-human hosts that amplify virus

Question 8

Three virus families of Arboviruses

Answer 8

1) Togaviridae: enveloped, EEE, WEE, VEE
2) Flaviviridae: St. Louis Encephalitis, West Nile Virus, Yellow Fever, Japanese Encephalitis
3) Bunyaviridae: California Encephalitis Virus (LaCrosse)

Question 9

Eastern Equine Encephalitis location and season

Answer 9

Eastern US
Summer-Fall in northern states, year-round in Florida
Common around Swamps

Question 10

Eastern Equine Encephalitis reservoirs and transfer to humans

Answer 10

Birds and Horses are reservoirs

Usual zoonotic cycle involves ornithophilic mosquitoes, so bridge vectors are required for human inoculation

Question 11

Eastern Equine Encephalitis most common ages for infection and expected outcomes

Answer 11

Most commonly: Children under 15 or adults over 55

Children more likely to survive than adults, but kids under 5 have severe sequelae–mental retardation, paralysis

Question 12

Western Equine Encephalitis location, reservoirs, season, and most common infected people

Answer 12

West of Mississippi
Summer-Fall preference
Bird, Horse, Small mammal
Most cases in kids under 10

Question 13

Western Equine Encephalitis sequelae

Answer 13

Sequelae uncommon in adults, but more common in kids

Recurrent convulsions, motor/behavioral changes in 50% of kids infected in first month of life

Question 14

Western Equine Encephalitis reservoirs that transfer to humans, vector, and common locations

Answer 14

Bird reservoirs, especially sparrows and house finches

Mosquito vector adapted to flooded grounds and irrigated pastures

Question 15

St. Louis Encephalitis location and season

Answer 15

Throughout US, but concentrated in Midwestern states in Ohio-Mississippi river valley down to the Gulf Coast
Summer-Fall preference
Sporadic outbreaks

Question 16

St. Louis Encephalitis most common host and vector and commonly infected humans

Answer 16

Bird Reservoir with mosquito vector
Sparrow most prevalent amplifying host
Infants and adults over 40

Question 17

West Nile Virus greatest risk factor for serious disease and death

Answer 17

Age > 50 years

Question 18

Common effects of West Nile Virus

Answer 18

Meningitis, Encephalitis

Paralytic syndrome similar to Polio with neuronophagia of anterior horn cells

Question 19

Diagnosing West Nile Virus

Answer 19

MAC-ELISA

Be careful of cross-reaction with other flaviviridae such as StLE and Yellow fever

Question 20

West Nile Virus hosts and vectors

Answer 20

Sparrows, mosquitoes

Question 21

Japanese Encephalitis location

Answer 21

Asia and western pacific

Question 22

Japanese Encephalitis reservoirs and vectors and season

Answer 22

Water bird, pig reservoirs
Mosquitos vector
Summer/Fall
In tropical regions, year-round

Question 23

Japanese Encephalitis symptoms

Answer 23

Most are asymptomatic
1:200 produce serious disease
Mostly in young children

Question 24

Japanese Encephalitis control and detection

Answer 24

Vaccines are available and are helpful for travelers

MAC-ELISA on serum or CSF

Question 25

California Encephalitis location, season, and infected persons

Answer 25

Widespread distribution through US and Canada, endemic in Midwest (LaCrosse serogroup)
Summer-Fall
School-aged kids 6 months – 16 years
Boys mostly

Question 26

California Encephalitis reservoir and vector

Answer 26

Small mammal reservoir, mosquito vector

Mosquito is a daytime feeder, breeds in tree holes, old tires, containers with water

Question 27

Colorado Tick Fever is what type of virus

Answer 27

Reovirus in the genus Coltivirus

Question 28

Colorado Tick Fever vector, reservoirs, areas, season, and common presenting symptom

Answer 28

Wood Tick vector
Squirrels and chipmunks reservoir
Mountainous regions
March–October
Frequently males 15-40, most have history of tick exposure
Saddle back fever pattern
Most patients recover without issue