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77 Cards in this Set

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What does arbovirus stand for?
Anthropod-borne virus
Give three examples of arbovirus groups.
Togaviruses (equine encephalitis)
Flavivirus (St. Louis encephalitis and west nile virus)
Bunyaviruses (do not need to know any detail)
Togaviruses and flaviviruses share which of the following characteristics: (one or more answers)
a. large
b. unenveloped
c. icosahedral nucleocapsid
d. single molecule of (-)stranded RNA
e. most toga-and flavi-viruses are arboviruses
a. No- small
b. No
c. Yes
d. No- single (+)stranded RNA
e. Yes
Define intrinsic and extrinsic incubation periods.
Transmission of arboviruses requires multiplication in the arthropod host. Thus, there are two incubation periods:
a. Intrinsic incubation period in humans: ~1wk or longer
b. Extrinsic incubation period in mosquito or other anthropod: ~14 days during whicn the arbovirus is multiplying in the anthropod.
Name 6 arboviruses that cause encephalitis.
Eastern equine encephalitis virus (EEE)
Western euqine encephalitis virus (WEE)
St. Louis encephalitis virus
West Nile virus
California group of encephalitis viruses
Venezuelan equine encephalitis virus (VEE)
How long is the intrinsic incubation period in arboviral encephalitis?
~ 1wk, relatively short for verimic infection
True or false:
Following the incubation period, the initial viremia results from multiplication in vascular endothelium.
Which virus causes the most deadly arboviral encephalitis?
Eastern equine encephalitis
How is EEE transmitted to the dead-end hosts, i.e. humans and horses?
When a mosquito bites a viremic wild bird, the EEE multiply in the mosquito. When the mosquito bite a human the virus is trasmitted.
True or false:

The best warning of impending EEE epidemics comes from finding a high prevalence of antiviral antibody in wild birds.
What are the standard controls during the EEE epidemic?
a. reduction of mosquito population
b. avoidance of mosquitoes during epidemic (e.g. insect repellent)
To which group(s) of viruses do West Nile virus and St. Louis virus belong?
Flaviviruses (single (+)stranded RNA)
Are humans dead-end hosts for St. Louis encephalitis and West Nile viruses?
True or false:
St. Louise encephalitis and West Nile viruses are found only in the mosquito of rural areas.
True or false:
St. Louis and West Nile viruses are fatal in most cases.
False. ~10% of the clinical cases are fatal. Many are subclinical.
True or false:
Western equine encephalitis virus infection is often fatal.
False. ~10% of the clinical cases are fatal. Many are subclinical.
True or false:
Eastern equine encephalitis virus infection is often fatal.
True. ~75% of clinical cases are fatal. Some are subclinical infections.
True or false:
Adults over 50yo is the dangerous age group for St. Louis encephalitis.
True or false:
Adults over 50yo and infants are the dangerous age group for West Nile virus infection.
False. The adults over 50 is the age group with highest incidence.
True or false:
Infants and adults over 50 yo have a high incidence of Western equine encephalitis.
True or false:
Eastern equine encephalitis occurs mostly in school-age children.
False- mostly children under 10.
LaCrosse virus has a high incidence in which of the following age group?
a. children
b. children under 3 yo
c. adults over 50 yo
d. all populations
a. children
What are the major vertebrate hosts for LaCrosse virus?
Hares and rodents
Where is the habitat of major mosquito vector for LaCrosse virus?
Rural forest
To which virus group does LaCrosse virus belong?
Bunyavirus- enveloped RNA virus (no further detail discussed in this course)
Also, it is a member of the California encephalitis virus group.
True or false:
In the temperate zones, arbovirus disease is seen as focal epidemics of short duration.
True. The conditions have to be just right to allow transmission.
True or false:
Outside the USA, arboviruses cause yellow fever or dengue fever, in addition to encephalitis.
True- both are flavivirus
Is classical dengue fever a life-threatening disease?
No, although it is a severe disease (a.k.a. "bone-break fever") it is NOT life-threatening.
Where does dengue fever occur most commonly?
in south east asia and the Caribbean islands
Are humans dead-end hosts for yellow fever or dengue flaviviruses?
Recently in SE Asia and the Caribbean, there has emerged a hemorrhagic dengue fever. Is this a fatal form? What are the characteristics that distinguish a hemorrhagic dengue fever from a classical form?
The hemorrhagic dengue fever is fatal and is characterized by hemorrhage, vomitting blood and shock.
A patient who travelled to the Carribean for spring break has been diagnosed with a dengue fever. Would you expect this patient to have a classic or a hemorrhagic dengue fever?
Most visitors get the classical mild disease. Although there has been no hard evidence it is likely that sequential infections with two different serologically cross-reacting dengue viruses would cause the hemorrhagic dengue fever.
How many corss-reacting antigenic types of dengue virus are there? What are they?
4 cross-reacting antigenic types (type 1,2,3,4)
How long is the incubation period for dengue fever virus?
one week
What are the common symptoms of a classical form?
Muscle pain
and rash
How long is the incubation period of yellow fever?
~7 days
What are the symptoms of yellow fever?
Characterized by fever, nausea and jaundice (from viral damage to liver cells).
Where is the initial multiplication site of the flavivirus causing yellow fever?
In vascular endothelial cells and the resultant viremia serves to infect the liver and other organs such as spleen and kidney.
How is the mortality rate of yellow fever?
Where are yellow fever found?
Rural tropical Africa and South America
Describe the pattern of transmission for yellow fever or dengue
-> Aedes aegypti (mosquito) -> humans -> Aedes aegypti -> humans
Jungle yellow fever has another cycle perpetuating the virus in tropical forests. What are the agents participating in this cycle?
-> monkey -> tree mosquito-> monkey -> tree mosquito -> humans -> Aedes aegypti -> humans
Is there a vaccine available for yellow fever?
Yes, an excellent live-attenuated vaccine (17-D vaccine) gives long-term protection.
What alert(s) the danger of yellow fever epidemics?
Aedes aegypti and unvaccinated person
a. vertical infection
b. horizontal infection
a. neonatal infections acquired from the mother
b. all other infections than vertical infections
What are two pathways that lead to vertical infection?
(a) perinatal pathway: neonate infected during birth by contact with maternal blood or other fluids. Similar to horizontal pediatric infections (b) transplancental pathway: the virus crosses the placenta to invade the developing fetus. Often distorts normal development resulting in congenital anomalies.
Which viruses can neonates contract in the perinatal pathway?
HBV, HIV and herpes simplex type 2
Which viruses can fetus contract in the transplacental pathway?
Parvovirus B-19
Rubella virus
Lymphocytic choriomeningitis virus
Is fetal infection common? Why or why not?
Fetal infections are uncommon because the placenta is a barrier to most viruses. Even the smallest viruses are impermeable across the placenta. But some viruses replicate in placental tissue.
Are most maternal viral disease threat to fetus?
No, as a substantial defense mechanisms, the developing fetus is well-protected against viral infections.
What are the substantial defense mechanisms a fetus use against viruses?
a. maternal IgG
b. Fetal antibody after fourth month (mostly IgM)
c. Interferon (probably adequate after 4 mo.)
d. Cell-mediated immunity
Parvovirus B-19

Enveloped or uneveloped
Nucleocapsid symmetry
Icosahedral virions
Linear single-stranded DNA
But little nucleotides to replicate its genome
What is the route of Parvovirus B-19 infection?
Inhalation of a respiratory aerosol from an infected person
What is the major damage done by the parvovirus-19?
The infection inhibits red blood cell production for about a week, by viral growth in the red blood cell precursors.
Which groups of patients are susceptible to fatal crisis during the parvovirus B-19 infection?
a. Patients with pre-existing deficits and abnormalities in red cell production.
b. Fetus
True or false:
Primary B-19 virus infection during pregnancy can lead to fetal death only in the 1st trimester.
False. Primary B-19 virus infection during pregnancy can lead to fetal death no matter when in gestation the infection takes place.
Fill in the blank:( ) is associated with fetal death caused by B-19 infection in the 1st and 2nd trimester.
Hydrops fetalis (severe edema). Infection in the third trimester can result in intra-uterine fetal death but hydrops is not seen.
Fill in the blank:
Rubella virus is a ( )-virus.
What is the main route of rubella virus transmission?
Rubella is transmitted by respiratory aerosols from an infected person. Unlike other togaviruses (e.g. EEE, VEE and WEE), there is no anthropod transmission.
Is viremia involved in the infection of rubella virus?
Yes, local multiplication in the respiratory epithelium is followed by viremia.
Which is less contagious: measles or rubella?
Rubella. There are persistence of seronegative adults.
How long is the incubation period for rubella?
18 days
What are the typical symptoms of rubella?
Rash that lasts about 3 days with a fever and lymphadenopathy
When are rubella-infected individual infectious?
One week before and after the rash. Sometimes rubella is subclinical.
True or false:
Rubella is sometimes more severe in adults, with transient arthritis.
Does subclinical infections of rubella virus produce lifelong immunity?
Is there a vaccine for rubella?
Yes, there is a live vaccine. It has been successful, and now rubella is very rare.
What is the cause of congenital rubella?
Rubella virus from the viremia of primary infection during pregnancy croses the placenta.
In addition to spontaneous abortion, spectrum of possible congenital anomalies are:
a. cataracts
b. heart defects, especially patent ductus arteriosus
c. deafness
d. retardation
The time of fetal infection of rubella virus is critical. Explain the statement.
Infection during the first month of gestation, 50% malfomration. 2nd month 25%. third month 9% and fourth month 4%.
True or false:
Rubella is not fatal in most people but its vaccination is important in creating a herd immunity because congenital rubella can have a severe consequence to a developing fetus.
True or false:
Virus production throughout gestation and gradually decreasing through first two years of life (mostly in urine)
In order to create herd immunity, two conditions are pursued in the United States. What is the plan?
a. nearly all children must be immunized
b. Individual immunity must be maintained through the child-bearing years to reduce the number of susceptible pregnant women.
What would you recommend about pregnancy for seronegative women of child-bearing age getting the vaccine?
To avoid pregnancy for two months.
Has there been reported cases of transplacental infection or congenital anomalies in vaccinated pregnant women?
Which group of individuals are susceptible to congenital rubella nowadays?
a. children whose parents do not allow immunization
b. rubella cases in immigrant children
c. sero-negative women of child-bearing age
True or false:
The use of MMR vaccine eradicated rubella, and rubella is no longer a major public health concern.
False: Rubella remains a major public health problem in many developing country.