DNA: Papovaviridate, Parvoviridae, Hepadnaviridae Flashcards
Papovaviridae
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
Human Papilloma Virus (HPV)
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
Progression of HPV infection
1) Papillomavirus
2) Inoculation of epithelium in hand, foot, throat, or cervix
3) Local multiplication
4) Wart formation
5) Resolution (Latency) or Cell transformation
What is Gardasil?
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.
Polyomaviridae
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
Parvoviridae
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
Hepadnaviridae
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
What are several antigens of the HBV virus?
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
DNA viruses and cancer
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
What are the best DNA virus candidates for causing human cancers?
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
What is unique about Baltimore Virus Groups III, IV and V?
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
Double stranded RNA viruses (Baltimore Class III)
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
Colorado Tick Fever virus?
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
Positive Strand ssRNA viruses (Baltimore Class IV)
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
Poliovirus (enterovirus)
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
Poliomyelitis
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)
How is poliomyelityis controled?
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.
What is post polio syndrome?
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
What do ECHO viruses lead to?
ECHO (Enteric, cytopathogenic, human orphan) viruses lead to:
Paralysis
Diarrhea
Aseptic meningitis
Common cold
What disease / condition is Enterovirus 70 linked to?
Hemorragic conjunctivitis
What disease / condition is Enterovirus 70 linked to?
Encephalitis
What are the symptoms of Coxsackie viruses A & B?
Aseptic meningitis
Common cold
Myocarditis
Herpangina
Pleurodynia
NOTE: Coxsackie virus A is associated with diseases involving vesicular lesions.
What is the Hepatitis A virus known for?
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.
What is the Rhinovirus known for?
This virus is acid labile and not shed in the stool like other picornaviruses.
It is transmitted by the respiratory route.
Grows at 33o C
Causes common cold, bronchitis, croup, bronchopneumonia
There are more than 200 serotypes
Most serotypes cause the common cold
Caliciviridae (Calix cup)
These are naked, icosahedral nucleocapsids
Slightly larger than picornaviruses and differ in macromolecule synthesis
What are the characteristics of norovirus?
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
What are the characteristics of Hepatitis E?
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
