Togaviridae, Flaviviridae, Coronaviridae, Paramyxoviridae, Orthomyxoviridae, Filoviridae, Bunyaviridae, Arenaviridae, Rhabdoviridae

Question 1

What are the charateristics of Togaviridae?

Answer 1

Enveloped, icosahedral nucleocapsid

Single strand, + sense, non-segmented RNA

Arboviruses and Rubivirus cause disease in man

Question 2

Describe the characteristics of Arboviruses?

Answer 2

Arboviruses multiply in mosquitoes and vertebrates

Most infections in natural reservoirs are subclinical

Virus causes zoonotic disease

Humans are usually incidental, dead-end host

Symptoms of the diseases caused by arboviruses are fevers and encephalitis

The primary arbovirus-caused diseases seen in the U.S. are Eastern, Western, and Venezuelan Equine Encephalitis.

Question 3

Describe the characteristics of Rubiviruses (rubella or German measels).

Answer 3

Rubiviruses spread via respiratory route and congenitally

They can result in congenital cataracts, deafness, congenital heart disease, cerebral damage and developmental delays in congenitally infected children.

There is a good, live attenuated virus vaccine (The R in MMR) to give to children and susceptible women of child bearing age

Question 4

What is the rubella rash?

Answer 4

These are thought to be immune complxes under the skin

They cause the rash and the arthralgia that is associated with rubella infection

Question 5

What are the characteristics of Flaviviridae?

Answer 5

Enveloped, icosahederal

Single stranded, non-segmented, + sense RNA

They cause fever, hemorrhagic fevers, or encephalitis

Some in this family are mosquito-borne (Yellow Fever, Dengue, St. Louis Encephalitis, Japanese B. Encephalitis, West Nile Encephalitis)

Antibody to Dengue may enhance disease and could lead to the hemorrhagic version of the disease

Some of these viruses are tick-borne.

These viruses cause several encephalitides in America including Powassan Encephalitis.

Hepatitis C is also a member of this family

Question 6

Describe the disease pathology of West Nile Virus.

Answer 6

About 20% of those infected will get a mild illness

Characterized by fever

Only 1 in 150 will get a severe infection with severe neurological manifistations

Advanced age is a risk factor for severe disease

Disease has spread to every state in America

Question 7

What are the pathological characteristics of Hepatitis C?

Answer 7

Causes acute (15%) and chronic (70%) hepatitis

Chronic cases may be asymptomatic for 10 to 30 years but cirrhosis is the result

Exposure to infected blood is the most common route of transmission

HCV can be passed sexually as well

Disease has a broad, global prevalence

Question 8

What are the characteristics of Coronaviridae?

Answer 8

Coronaviridae are helical, enveloped viruses

There RNA is single stranded, non-segmented and + sense

They cause some mild upper repiratory tract infections

15% of common colds are due to this virus

Some cause enteric disease

Numerous serotypes in this family

Question 9

What are the characteristics of SARS (Severe AcuteRespiratory Syndrome)?

Answer 9

It is a coronavirus

Causes severe respiratory illness

Fevers >100.4^o C

One or more clinical findings: Cough, SOB, difficulty breathing or hypoxia

Question 10

What are the characteristics of Middle East Respiratory Syndrome (MERS)?

Answer 10

MERS is a viral disease caused by a coronavirus called MERS-CoV

First reported in Saudi Arabia in 2012

Most infected develop severe acute respiratory illness.

Have fever, cough, and SOB

About 1/2 of infected die

Question 11

What are the characteristics of Orthomyxoviridae?

Answer 11

Orthomyxoviridae are enveloped, helical

Have single stranded RNA that is segmented (8 segmets) and is - sense

Three viruses cause disease: Influenza A, B, and C (Influenzaviridae)

Question 12

What are the characteristics of influenzaviridae?

Answer 12

The influenzaviridae have segmented, - sense RNA broken up into 8 segments

Have a helical nucleocapsid that is enveloped

Nucleocapsid protein (NP) puts capsid together

Two types of glycoproteins stud the outter envelope: Hemagglutinin Activity (HA) and Neuraminidase Activity (NA)

M-proteins anchor the base of each of these glycoproteins inside of the viral envelope

Question 13

What is Hemagglutinin Activity (HA) used for?

Answer 13

HA attaches to host cell sialic acid receptors

Present on the surface of erythrocytes and upper respiratory tract cells so HA causes blood cells to agglutinate

Binding of HA to sialic acid receptors causes the fusion of the host cell membrane with the virion membrane

HA is needed for viral adsorption

Question 14

What is Neurominidase Activity (NA) used for?

Answer 14

NA cleaves neuraminic acid and disrupts the mucin barrier covering respiratory epithelial cells

This allows the influenza virus to fuse with and enter these cells

NA is also needed for the release of new virions

NA cleaves the salic acid receptor that HA is bound to and allows the newly budded virus to escape the cell

Question 15

How many types of influenzae are there?

Answer 15

Three: Influenza A, B, and C

Influenzea A is the primary cause of human disease but also infects other mammals and birds

Influenza B and C have only been isolated from humans

Question 16

How do influenza viruses gain virulence?

Answer 16

Antigenic Drift

Antigenic Shift

Question 17

What does antigenic drift mean in the context of influenza virus?

Answer 17

During viral replication, mutations can occur in the HA or NA leading to changes in the antigenic nature of these glycoproteins.

These changes are small and resulting strains will be partially attacked by the immune system

Due to point mutations or changes in RNA at a single base

Question 18

What is antigenic shift?

Answer 18

Atigenic shift refers to a complete change in the HA, NA or both.

Occurs in Influenza A because of the swapping of RNA segments (gene reassortment) between animal and human strains of the virus.

This results in a novel virus and is a major genetic change.

This is the cause of pandemics

Question 19

What is the route of infection of influenza?

Answer 19

Infected aerosol droplets (90% attack rate in close quarters)

Question 20

How are influenza viruses named?

Answer 20

1) A, B, or C determined by nucleoprotein antigen
2) Second part of name is animal host of origen if other than man
3) Geographical origin
4) Strain number
5) Year of isolation
6) Within each type, strains or subtypes are defined by antigenic specificities contained in the HA and NA antigens (B is not typed this way)

Example: A/Singapore/1/57/(H2N2) & A/Hong Kong/1/68/(H3N2)

Question 21

What are the characteristics of Paramyxoviridae?

Answer 21

Paramyxoviridae are helical, enveloped, and have single stranded, nonsegmented - sense RNA

Cause cells to form syncytium due to the F or fusion protein on the surface of members of this family

Parainfluenza (Paramyxovirus) viruses cause respiratory infections in humans, croup, common cold. Infect the upper respiratory tract but rarely cause viremia.

Virus is cytopathic

Mumps (Paramyxovirus) is another member of this family that causes disease in humans. Causes parotitis, orchitits, menigoencephalitis, and pancreatitis

Route of spread of mumps is upper respiratory tract to mucous membranes, then viremia, then to salivary glands

Measles (Morbillivirus) is another member of this family

Respiratory syncytial virus (Pneumovirus) is also a disease causing member of this family

Question 22

What is the route of infection of measles (Rubeola)?

Answer 22

Upper respiratory tract, then viremia, then skin

This is one of the most highly communicable of all diseases

Maternal antibody protects the infant until the age of 6 months

The measels rash is caused by T cell response to virus infected epithelial cells lining the capillaries

Question 23

What does respiratory syncytial virs (RSV) cause?

Answer 23

Pneumonia and bronchitis in infants and young children

Common cold

Major cytopathic effect is syncytia formation

Most important respiratory tract pathogen in children with 20-30% of respiratory illness in children resulting from RSV

Question 24

What are the characteristics of Rhabdoviridae?

Answer 24

Bullet-shaped, enveloped helical capsid

• sense, single stranded, non segmented RNA

Rabies virus is most important human pathogen - Fatal except in 2 or 3 cases

Spread via broken skin and sometimes aerosols from bats in caves

Reservoirs are raccoons, skunks, foxes, and bats

Bat bites most common route of spread in US; dog bites in other countries

Question 25

What is the pathogenesis of rabies?

Answer 25

Bite implants infected saliva in muscle near nerves

Virus multiplies in muscle tissue near bite; incubation period is 10 to 240 days

Virus travels thru axons to the CNS where it replicates in neurons of gray matter and often forms cytoplasmic inclusions in the hippocampus and cerebellum

Migrates to invade a variety of organs and tissues, including salivary glands

Question 26

What are the clinical manifestations of rabies?

Answer 26

Prodromal - Nonspecific, may have abnormal sensations at bite site

Excitation phase - Increasing anxiety, eye problems, hydrophobia

Paralytic phase - Progressive general flaccid paralysis. Apathy to stupor to coma. Peripheral vascular collapse and death.

Question 27

True or False: Rabies virus can be transmitted via the respiratory route.

Answer 27

True; This is a rare mode of transmission.

Bats may have persistent infections and the virus is shed in the urine. If this urine is inhaled, one can be infected.

Lab workers have contracted rabies from aerosols of the virus and have required corneal transplants

Question 28

How is rabies diagnosed and treated?

Answer 28

History of bite by known rabid animal or exposure to a bat

Symptoms

Classical clinical lab findings are of no value

ID of virus by fluorescent antibody test on body tissue or isolation of virus from secretions

Prognosis - Almost universally fatal but there is an inactvated rabies virus vaccine for those especially at risk

Wash wound with quaternary ammonium salts after a soap and water wash

Use human rabies immunoglobulin in addition to vaccine

Question 29

How can rabies be controled?

Answer 29

Vaccinate cats and dogs

Eliminate stray animals

Oral vaccine used in some areas of Europe and US for wild animals

Question 30

What are the characteristics of Filoviridae?

Answer 30

Thread-like filaments

Have a helical capsid

Single stranded, nonsegmented - sense RNA

Cause acute hemorrhagic fevers in humans and mokeys

Natural reservoir is unknown

Marburg - 1967 in Germany. Infected workers in a factory producing poliovirus from monkeys

Ebola - 1976 Zaire and Sudan. Sporadic outbreaks since then in Zaire, Gabon, and Uganda

Question 31

What are the characteristics of Bunyaviridae?

Answer 31

These have a helical, enveloped capsid

Single stranded, segmented - sense RNA but can be - and + sense

Viruses are pleomorphic with n o matrix proteins. Reassortment between strains is common.

Two major groups:

Arboviruses - Arthropod borne (Cause LaCrosse encephalitis / California encephalitis)

Hantaviruses - Rodent borne. No arthropod vector. Transmitted via aerosolized rodent urine and feces droppings.

Question 32

What are the characteristics of Arenaviridae?

Answer 32

Helical, enveloped capsid

Single stranded, segmented, - sense

Lassa Virus (Africa & S. America) - Hemorrhagic fevers, often fatal

Lymphocytic choriomeningitis (LCM) - Flu-like symptoms or uncommonly, meningoencephalitis in humans. This virus has been important in the concept of immunological tolerance

Rodents are the usual reservoirs of these viruses but they don’t get sick. Pass virus in droppings and urine.

Question 33

What are the characterisctics of Hepatitis D virus?

Answer 33

HDV is enveloped and RNA is circular, single stranded - sense

It is not infectious by itself; must co-infect with Hepatitis B

Discovered in the late 70s in the nuclei of hepatocytes of Hep B patients

Its envelope protein is serologically indistinguishable from HBsAG

Question 34

What are the types of RNA virus genomes?

Answer 34

+ and - sense

Single stranded and double stranded

Question 35

What does + sense mean in relation to the RNA genome of an RNA virus?

Answer 35

This means that the RNA is essentially a mRNA that can be immediately translated by host cell ribosomes.

Question 36

What does - sense mean in relation to the RNA genome of an RNA virus?

Answer 36

• stranded RNA cannot begin translation immediately. They must first be transcribed into a + sense strand of RNA.

These viruses carry an RNA-dependent RNA polymerase that transcribes the - strand into a + strand

Question 37

True or False: Most DNA viruses are both + and - sense.

Answer 37

True: The positive strand is the strand that is used as the template strand to be transcribed into mRNA

Once the mRNA has been transcribed, it can be translated by host cell ribosomes

The - sense strand is just “there”