DNA: Papovaviridate, Parvoviridae, Hepadnaviridae

Question 1

Papovaviridae

Answer 1

Structure: Naked icosahedral nucleocapsid (smaller than adenoviridae)

DNA may integrate into host DNA and may contribute to oncogenesis

Produce latent & chronic infections

Cells are often transformed if virus can’t matre

Family consists of papillomavirus and polyomaviruses

Question 2

Human Papilloma Virus (HPV)

Answer 2

Usually cause benign skin warts and genital warts (condyloma acumata)

Some HPVs are sexually transmitted and can cause cervical cancers. The ones that cause cervical cancers rarely cause genital warts.

Human cells may not be 100% permissive to these HPVs

HPV can cause epidermosdysplasia verruciformis - These are multiple skin warts which can progress to squamous carcinoma

Question 3

Progression of HPV infection

Answer 3

1) Papillomavirus
2) Inoculation of epithelium in hand, foot, throat, or cervix
3) Local multiplication
4) Wart formation
5) Resolution (Latency) or Cell transformation

Question 4

What is Gardasil?

Answer 4

Gardasil is a vaccine that is available to prevent infection by HPV 6, 11, 16, and 18.

These cause ano-genital warts and cervical cancer.

Question 5

Polyomaviridae

Answer 5

The viruses JC and BK cause inapparent human infections

Probably via respiratory tract.

They infect lymphocytes and kidney with minimal cytopathic effects.

BK establishes a latent infection in kidney while JC establishes latent infection in kidney, B cells, and monocytes

In immunocompromised people, viruses can reactivate

Question 6

Parvoviridae

Answer 6

Structure: Naked icosahedral nucleocapsids

Parvovirus B19 causes erythema infectiosum (5th disease, slapped cheek disease) in children

Viremia occurs and the virus replicates in rapidly dividing erythroid precursers and there is a temporary halt in erythrocyte production

Permanent immunity exists after infection

In adults, infection is often subclinical and in pregnant women, infection can result in the death of the fetus

Question 7

Hepadnaviridae

Answer 7

Icosahedral enveloped virus

Has a unique, nicked, circular DNA

Uses reverse transcriptase to replicate an RNA intermediate

Difficult to study- Canbe grown in vitro using transfection

Hepatitis B is the human member of this group; causes serum hepatitis or long-incubation hepatitis

Transmission may be veneral or congenital. Blood is also an important mode of transmission.

There is a vaccine avaliable

Virus replicates in hepatocytes w/ minimal cytopathic effects. Viral DNA may integrate into hepatocyte chromosome and remain latent.

Cell mediated immunity and inflammation are responsible for HBV symptoms

Question 8

What are several antigens of the HBV virus?

Answer 8

HBcAg - Core antigen (capsid)

HBe-Ag - May be a breakdown product of core antigen

HBsAg - Surface antigen (Serves as a decoy particle and interferes with teh host immune system)

5 to 10% of infected as adults will get chronic infection and shed surface antigen and virus

70-90% will get chronic infection if they contract the virus perinataly

Chronic HBV results from a week cell mediated immune system and predisposes the person to more serious outcomes

Carriers are at a high risk for chronic liver disease and primary hepatocellular carcinoma. Can be caused by virus inserting into chromosome.

Coinfection with Hepatitis D may worsen the course of disease

Question 9

DNA viruses and cancer

Answer 9

DNA viruses cause tumors in conjunction with other risk factors

Depending on the type of virus, DNA of tumor causing viruses may be integrated or free in the nucleus as an episome

Some viruses carry genes that immortalize cells and cause them to divide continuously

Question 10

What are the best DNA virus candidates for causing human cancers?

Answer 10

Hepatitis B

HPV 5, 8, 9, 12, 14, 15 - epidermodysplasia verruciformis

HPV 16 and 18 - cervical cancer

Human Herpesvirus 8 - Kaposi sarcoma

Epstein Barr virus - Undifferentiated nasopharyngeal carcinoma and African Burkitts lymphoma

Question 11

What is unique about Baltimore Virus Groups III, IV and V?

Answer 11

Generally replicate in cytoplasm of infected cells and do not integrate with host genetic material

Genetic material replicates by synthesis of complementary RNA. DNA is NOT involved

Code for RNA-dependent RNA polymerases which codes for mRNA

These viruses show high mutation rates because of a lack of proofreading enzymes

Question 12

Double stranded RNA viruses (Baltimore Class III)

Answer 12

Reoviridae (Respiratory Enteric Orphan)

Naked nucleocapsids with two icosahedral capsid shells

Rotavirus causes disease in infants via fecal-oral route. Major cause of gastroenteritis.

Two vaccines available: Rotarix and RotaTeq

NOTE: Orthoreovirus and Orbivirus / coltvirus also cause disease

Question 13

Colorado Tick Fever virus?

Answer 13

Orbivirus

Found throughout the western U.S.

Vector is Dermacentor andersoni whick is also the vector for Rickettsia

Illness occurs 3-6 days after tick bite

Headache, muscle pains, fever, and sometimes encephalitis

Question 14

Positive Strand ssRNA viruses (Baltimore Class IV)

Answer 14

RNA alone is infectious; it acts as mRNA

1) Picornaviridae (Small RNA viruses) - Naked icosahederal nucleocapsid. Usually cytolytic infections.

Enteroviruses- acid stable, resistant to harsh environments and transmitted fecally-oral

Question 15

Poliovirus (enterovirus)

Answer 15

Three serotypes

In 95% of people, causes inapparent infection

4-8% mild disease

1-2% nonparylytic aseptic meningitis

In less than 1% of people, it causes flaccid paralysis

Question 16

Poliomyelitis

Answer 16

Acute illness involving meningesi and replicates in the motor neurons of the anterior horn of the spinal cord and brain stem. may produce permanent paralysis.

Naturally occuring wild-type cases have been eliminated in Western nations

Cases caused by live oral vaccine can still occur (VAPP-vaccine associated paralytic polio)

Question 17

How is poliomyelityis controled?

Answer 17

Enhanced inactivated vaccine (Salk eIPV)

Live attenuated vaccine (Sabin OPV) - This can revert and cause paralytic polio

IPV is recommended to prevent VAPP but does not provide good mucosal immunity in GI tract. Vaccinated individuals can contract virus and excret it but not get disease.

Question 18

What is post polio syndrome?

Answer 18

25-35 years after recovery, there s a gradual progression of muscle weakness

Cause not fully understood

Theory is that there may be a small, surviving pool of polio in motor neurons

Question 19

What do ECHO viruses lead to?

Answer 19

ECHO (Enteric, cytopathogenic, human orphan) viruses lead to:

Paralysis

Diarrhea

Aseptic meningitis

Common cold

Question 20

What disease / condition is Enterovirus 70 linked to?

Answer 20

Hemorragic conjunctivitis

Question 21

What disease / condition is Enterovirus 70 linked to?

Answer 21

Encephalitis

Question 22

What are the symptoms of Coxsackie viruses A & B?

Answer 22

Aseptic meningitis

Common cold

Myocarditis

Herpangina

Pleurodynia

NOTE: Coxsackie virus A is associated with diseases involving vesicular lesions.

Question 23

What is the Hepatitis A virus known for?

Answer 23

Hepatitis A or infectious hepatitis, is a GI virus that is spread via fecal to oral route.

It is a picornavirus but is not cytolytic. It is released by budding.

Causes an acute infection.

Question 24

What is the Rhinovirus known for?

Answer 24

This virus is acid labile and not shed in the stool like other picornaviruses.

It is transmitted by the respiratory route.

Grows at 33^o C

Causes common cold, bronchitis, croup, bronchopneumonia

There are more than 200 serotypes

Most serotypes cause the common cold

Question 25

Caliciviridae (Calix cup)

Answer 25

These are naked, icosahedral nucleocapsids

Slightly larger than picornaviruses and differ in macromolecule synthesis

Question 26

What are the characteristics of norovirus?

Answer 26

Norovirus is a member of the caliciviridae family.

Spread via the fecal to oral route

60% of non-bacterial gastroenteritis can be attributed to the Norwalk virus

Very resistant to disinfection and can persist in environment for weeks

Some infected individuals can shed virus for weeks

Question 27

What are the characteristics of Hepatitis E?

Answer 27

Hepatits E is a member of the Calcivirus-like family and is unenveloped

Causes epidemic outbreaks of acute hepatitis in parts of the world with poor sanitation

Spread fecally-orally

Infection is frequently subclinical but when it is symptomatic, it causes acute disease

Can be fatal to pregnant women