Microbiology Flashcards
1
Q
What are the 3 classifications of herpesviruses?
A
- Based on genome arrangement and latency tropism
- Alphaherpesvirinae: neurotropic latency, aggressive lytic growth -> Herpes simplex virus (HSV)-1, HSV-2. Varicella-zoster virus (VZV)
- Betaherpesvirinae: lymphotropic for latency, more insidious -> Cytomegalovirus (CMV), Human herpes-virus-6 (HHV-6), HHV-7
- Gammaherpesvirinae: lymphotropic for latency, more insidious -> Epstein-Barr virus (EBV),** HHV-8 (Kaposi’s sarcoma-associated herpesvirus)**
2
Q
What are the structure, genome, and replication cycle of Herpesviruses?
A
- Structure: icosahedral capsid surrounded by lipid envelope with about 12 virus-encoded glycoproteins
- Genome: large, linear, dsDNA ca. 150-250 kb pairs
- Replication: genome replicated, viruses assembled in the nucleus
- Self-limiting infections in which primary infection is often asymptomatic -> BUT, life-threatening infections or cancers can occur, especially in immune compromised hosts
2
Q
What is Crimean-Congo Hemorrhagic Fever Virus?
A
- Transmitted by ticks in Middle East, Africa & Europe
- Clinical disease rare, but severe in infected humans, with a 30% mortality rate
- Targets liver and vascular endothelium
- Symptoms include: headache, pain in limbs, and often bleeding from many orifices
3
Q
What is the epidemiology of EBV?
A
- Poor: infection at early age; Rich: adolescence or early adulthood -> both can lead to infectious mononucleosis
- 90 to 95% adult population contains antibody to EBV
- Can cause oral hairy leukoplakia in immuno-compromised hosts
- Posttransplant lymphoproliferative disease (PTLD) in some transplant patients
- Associated w/Burkitt’s lymphoma, nasopharyngeal carcinoma
3
Q
What other two diseases might EBV be linked to?
A
Hodgkin’s lymphoma
Multiple sclerosis
4
Q
What is the epidemiology of CMV?
A
- CMV is not highly contagious
- Infection by socioeconomic class:
1. Low: infection 1-2 y/o, up to 80% adults CMV+
2. High: infection 16+ y/o, about 50% adults CMV+ - CMV in: saliva, urine, breast milk, semen, cervical secretions, blood, (transplanted organs)
- At risk populations: neonates, day care workers, gay men, pregnant workers, immunocompromised patients
5
Q
What are the epidemiology and expressions of classical and US KS?
A
- Classical: Mediterranean pop and sub-Saharan Africa; NOT sexually transmitted in these cases
- US: most KS pts are AIDS pts; sexually-transmitted, but virus absent from semen and vaginal secretions
- Virus in saliva; how sexually transmitted not known -> typically, 10 year incubation period before KS
- May be relatively mild, but if pt severely compromised, can be life-threatening -> AIDS and non-AIDS forms, 95% of infections are asymptomatic
- Must have immune system loss for disease symptoms (old age in classical forms, and AIDS in gay populations)
- When symptomatic, tx in AIDS pts is tumor-specific (resection, chemotherapy) or targets HIV, but not HHV-8
5
Q
What are the symptoms and diagnosis of yellow fever? Prevention?
A
- SYMPTOMS: “flu-like” malaise progressing to severe hemorrhagic fever, hemorrhage of stomach lining often results in “Black Vomit”
- Progressive liver involvement results in marked jaundice with increasing levels of serum transaminases owing to direct viral-mediated liver damage.
- Once hepatorenal disease progresses, mortality rate can be 20%-50% w/death 7-10 dd after symptom onset
- DIAGNOSIS** **via any 1 of the following: virus isolation (i.e. incubating blood sample with cell lines to observe CPE), serologic identification -> ELISA for IgG or IgM, detection of viral genomic sequences by RT-PCR
- Fortunately there is an effective and safe attenuated, live vaccine
7
Q
How does CMV affect immunocompromised hosts?
A
- Especially at risk
- Most organ transplant pts get CMV, with pneumonitis representing the most life-threatening aspect
- Can result from infection by CMV+ donor or by reactivation of CMV+ recipient
- Prophylactic tx w/CMV Ig and ganciclovir looks promising in limiting complications
- When you think transplant patient, think CMV!
- AIDS pts prone to CMV retinitis, colitis, pneumonitis
7
Q
Why do we think HHV-8 linked to Kaposi’s sarcoma? What is KS?
A
- Evidence indicates HHV-8 is necessary, but not sufficient to cause Kaposi’s sarcoma (KS)
1. DNA sequences can be recovered from >95% of AIDS and non-AIDS KS tumors
2. >80% seropositivity among KS patients, - B-cell and endothelial latency tropism: KS tumors occur in lining of lymphatic system -> channels fill with blood cells, hence bluish, bruised lesions
7
Q
What is Hemorrhagic Fever with Renal Syndrome?
A
- Caused by Hantavirus, and found primarily in Europe and Asia
- Human infection from exposure to aerosolized urine, droppings, or saliva of infected rodents, or after exposure to dust from their nests
- Symptoms usually devo 1 to 2 weeks after exposure:
1. Liver and vascular endothelium targeted
2. Symptoms include: fever, hemorrhage, acute renal failure - Over **15% mortality rate **
8
Q
Describe the replication cycle of Faviviridae.
A
- Entry via rec-mediated endocytosis; nucleocapsid into cytoplasm after pH-dependent fusion event
- Genomic RNA 5’-cap (like host mRNAs) and translated by host ribosomes to generate single polyprotein, that is cleaved by combo of viral (cis-cleavage) and host (trans-cleavage) proteases
- Cleavage of polyprotein generates viral RNA- depend RNA polymerase which replicates the genomic RNA
- Structural proteins (capsid, envelope gps), also derived from polyprotein, assemble genomic RNA into virions that “bud” into ER or Golgi; enveloped viruses released from cells following transport to the cell surface
8
Q
What is classical Dengue Fever?
A
- Self-limited infection begins abruptly after 2-7 day incubation period w/high fever, headache, retrobulbar pain, lumbosacral aching, conjuctival congestion, and facial flushing
- Mottled rash may appear on day 1 or 2 and often pts complain of a metallic taste in their mouths
- Fever may be sustained for up to 6-7 days, but usually abates with cessation of viremia
- Initial symptoms followed by generalized myalgia with increasing severity of muscle and joint pain -> called “bonebreak fever” due to severity of the bone pain
- Characteristic finding: thrombocytopenia (< 100x109/L)
- Recovery complete but slow, w/fatigue, exhaustion often persisting for 2 weeks
8
Q
What are the 4 minimum WHO criteria for diagnosis of DHF?
A
- Fever
- Hemorrhagic manifestations (e.g., hemoconcentration, thrombocytopenia, positive tourniquet test)
- Circulatory failure (e.g. hypoproteinemia, effusions)
- Hepatomegaly
9
Q
What are the target organs and disease course of Flaviviridae?
A
- Initially replicate at site of inoculation (endo/epi cells around bite site) and establish transient primary viremia
-
3-7 days post-exposure, replicates in macros, spleen, or lymph nodes:
1. Results in a mild systemic disease
2. Most infections dont progress beyond this point - If infection not controlled by immune response, then secondary viremia ensues
- Secondary viremia results in severe systemic disease (e.g. hemorrhagic fever/shock syndrome).
10
Q
What are Bunyaviridae?
A
- Enveloped, spherical particles w/segmented, single-strand, negative-sense RNA genomes
- 300 different species grouped into five genera:
1. Rift Valley fever virus: mosquitoes (Africa)
2. Crimean-Congo virus: ticks (Africa, Middle East)
3. Hemorrhagic fever with renal syndrome (HFRS) virus (Hantavirus): rodents (Asia & Europe)
12
Q
What are Foscarnet and Cidofovir?
A
-
Foscarnet: approved for CMV retinitis tx in AIDS pts
1. Pyrophosphate analog inhibits DNA polymerase, but does not require phosphorylation for activity - Cidofovir: deoxycytidine analog
- Competitive inhibitor of CMV (and HSV) DNA polymerase, but does not require viral kinase action for activity
- Approved for CMV retinitis treatment in AIDS patients
13
Q
What is Dengue?
A
- Dengue fever, severe form called dengue hemorrhagic fever (DHF) have emerged as the most important arthropod viral diseases of humans
1. Up to 100 million cases of dengue and 250,000 cases of DHF occur annually world-wide
2. Primarily South America, Southeast Asia, Africa
3. Most cases in the U.S. acquired abroad - Four serotypes of Dengue virus (DEN 1, 2, 3 & 4).
14
Q
Describe the Herpesvirus replication cycle.
A
- Undergo lytic replication in variety of cell types to propagate virus
- After attachment, penetration via virus gp-mediated fusion of envelope and PM -> released nucleocapsid migrates to nuclear envelope via microtubules, uncoats, and DNA enters nucleus, and virion components shut off host macromolecular syn
- Programmed expression of viral genes- cascade regulation
- Immediate early (IE) genes: virus-specific TF’s; use host RNA polymerase II, stimulate transcription at virus early promoters
- Early genes: encode nonstructural proteins, enzymes, DNA replication machinery, incl viral DNA polymerase, thymidine kinase (tk) which phosphorylates a variety of nucleotides besides thymidine
- Late genes: also dependent on IE TF’s plus genome replication for expression; encode structural proteins (capsids, glycoproteins); viral gps incorporated into virus envelopes and transported to cell surface where they can cause syncytia formation
- Virus assembly in nucleus, where nucleocapsids bud into perinuclear space -> migrate to cell surface and are released
15
Q
What cancer might CMV be associated with?
A
Glioblastoma multiforme
16
Q
How is EBV linked to Burkitt’s lymphoma?
A
- Burkitt’s is a neoplasm of B-cells that affects bones of the jaw, and is endemic in central Africa, New Guinea
- Associated with three factors:
- Early EBV infection leading to latency
- Activation of c-myc
- Malaria
- Early detection allows cure rate of 80%
- Outside of Africa, only 20% of BL patients have EBV genomes in tumor
17
Q
What is the treatment for EBV?
A
- Supportive for mono; withhold athletes due to possible inflammation of spleen
- Treatment of oral leukoplakia is with acyclovir
18
Q
What are the symptoms of Rift Valley Fever Virus in humans?
A
- Acute, self-limiting febrile illness w/flu-like symptoms
- Rarely (2%), symptoms progress to a severe form of disease that culminates in hemorrhagic hepatitis
1. As symptoms progress, often mistaken for early stage meningitis (e.g. stiff neck, photophobia, vomiting) - Symptoms often include: fever, encephalitis, and etinal vasculitis (which may lead to blindness)
- No established course of tx for pts infected with RVFV
20
Q
How do you diagnose CMV infection?
A
- ELISA or PCR detection
- Shell vial assay: indirect immunofluorescence used to detect immediate early protein after 24 h of cell culture infection
22
What is Ganciclovir?
- **Ganciclovir** guanosine analog similar to acyclovir, the prototype used in HSV, VZV, and EBV infections
1. Needs phosphorylation by viral kinase for activity
2. Triphosphate form _preferentially inhibits CMV polymerase_, but is more toxic to host than ACV
3. _Side effects_: neutropenia, GI tract bleeding
4. Approved for tx of **transplant patient infections**
5. Approved for CMV **retinitis** treatment in AIDS patients
23
What is the alternative to the Herpesvirus lytic replication cycle?
- All herpesviruses also undergo latency in which entire _genomes maintained extrachromosomally_ in the host indefinitely, but no viruses are produced
- _Three stages of latency_: establishment, maintenance, reactivation
- _Reactivation_ generally occurs in lapse in immunity -\> production of virus particles and recurrent infection
- Due to latency, anyone infected with a herpesvirus is **infected for life** and runs the risk of having recurrent infections or other sequelae (such as cancer)
23
What is the epidemiology of Rift Valley Fever Virus?
- Important veterinary pathogen in Africa -\> causes **abortion in livestock** (cattle, sheep & goats)
- **NOT in US**; considered potential bioterrorism agent
- Majority of human infections (in endemic areas) have resulted from direct or indirect contact with the blood or organs of infected animals (primary infection route of livestock via mosquitoes)
- **Vaccines available**, and immunization of livestock is most effective way to control and prevent the disease
25
How are Flaviviridae transmitted?
- All members of flavivirus genus transmitted by **insect vectors**:
1. Most important group of **arboviruses** (arthropod-borne viruses) in terms of disease causation
2. **Dengue fever** second only to malaria in terms of importance as a tropical disease
3. Many flaviviruses are considered _"emerging" viruses_
27
What are the pathogenesis and symptoms of EBV?
- _Pathogenesis_: spread via saliva by kissing with incubation period of 4-7 weeks
1. Initial replication in _oropharyngeal epithelium_
2. Spread to lymphocytes, then liver and spleen
3. Remains **latent in throat epithelium and B-cells**
4. Oral shedding of virus occurs for many weeks
- _Symptoms_: most infections asymptomatic or _infectious mononucleosis_ (sore throat, fever for one to two weeks, malaise, lymphadenopathy, with uneventful recovery)
29
How would you diagnose EBV infection?
- Based on symptoms and presence of _\>50% atypical, large lymphocytes with lobulated nuclei_ -\> T-cells responding to infection, not infected B-cells
- _Important antigenic markers_:
1. **EBNA** – _EBV nuclear Ags early in primary infection_
A. EBNA 1 maintains genome replication in dividing B-cells
B. Conversion to anti-EBNA IgG indicates resolution of primary infection
2. **VCA** – viral capsid antigen
A. Anti-VCA IgM indicates primary infection
B. Anti-VCA IgG w/o anti-EBNA = primary infection
C. Anti-VCA IgG + anti-EBNA IgG = past infection
3. **EA** – early Ag in cells that do not produce virus
- Dx can also incl looking for _heterophile antibodies_ (**Monospot test**) that agglutinate sheep red blood cells
1. Not in all pts, & origin not understood, but if present, distinguish EBV mono from CMV mono
30
What is DHF?
- Characterized by diffuse capillary leakage of plasma, and hemorrhagic diathesis
- Abdominal pain with restlessness, change in mental status, hypothermia, and **drop in platelet count** signals devo of DHF -\> if untreated, DHF most likely progresses to **dengue shock syndrome**
- INC vascular permeability = hemoconcentration, DEC effective blood volume, tissue hypoxia, lactic acidosis, and **shock**
- Common symptoms in impending shock: _abdominal_ _pain, vomiting, and restlessness_; may have symptoms related to circulatory failure
- _\>90% of cases of fatal DHF, evidence that person had been infected previously_ w/at least one heterologous dengue serotype -\> indicates that **immune-mediated pathology** initiates events causeing hemorrhagic syn
31
What is yellow fever? What are its transmission cycles?
- South, Central America, Africa -\> first virus shown to be transmitted via insect vector
- **3 transmission cycles**: jungle (sylvatic), intermediate (savannah), and urban
1. _Jungle (sylvatic)_: transmission b/t nonhuman primates (e.g., monkeys) and mosquito species in forest canopy -\> mosquitoes from monkeys to humans when humans visiting, working in jungle
2. _Intermediate (savannah)_: virus from mosquitoes to humans living, working in jungle border areas. Can be transmitted from monkey to human or from human to human via mosquitoes
3. _Urban_: virus b/t humans and urban mosquitoes, primarily Aedes aegypti. Virus usually brought to urban setting by viremic human who was infected in the jungle or savannah
32
How is dengue diagnosis confirmed?
- _Signs and symptoms non-specific_, and can be easily confused with those of malaria, leptospirosis, typhoid fever, etc., so **lab confirmation important**
- Serodiagnosis made on the basis of a _\>4-fold rise in antibody titer_ in paired IgG or IgM specimens.
- _Other diagnostic methods_: **culture of virus** from serum (or autopsy tissue), detection of viral genome seqs by **RT-PCR**
- Dengue a **reportable disease** in the US; known or suspected cases reported to public health authorities
33
What are the pathogenesis and symptoms of CMV?
- **Pathogenesis**: infection via _direct contact with secretions_, not by aerosol, and primary replication in epithelial cells, then spread to lymphoid tissue
1. Latently infects B-cells, T-cells, monocytes, and lymphocytes where it causes _large, puffed up cells_
- **Symptoms**: neonatal infections can occur in utero (most _asymptomatic_, but can cause retardation and deafness); most adult infections also asymptomatic, but _mononucleosis_ accompanied by fever can occur
34
How is EBV related to PTLD? What is the treatment?
- Uncontrolled proliferation of B cells b/c transformation by EBV and the absence of CTLs to control them
- _Highest risk in seronegative transplant recipients in the first year_
- Treatment: _stop immunosuppression!_
1. Must monitor for rejection
2. ACV not useful because infection is latent, virus is not replicating
36
What are Flaviviridae?
- Small, enveloped, nonsegmented, **+ strand RNA virus**
- Three genera:
1. Flaviviruses --\> Over 70 members, many of which cause disease in humans
A. **Dengue virus & Yellow fever virus**
B. Encephalitis viruses
2. Pestiviruses --\> Cow, pig, and sheep pathogens
3. Hepatitis C virus
37
How do the replication and disease of the Bunyaviridae work?
- Replication strategy similar to that of other (-) strand RNA viruses, but genes on 2-3 separate RNA segments
- Virus binds and is **endocytosed**
- Low pH in endosome triggers conformational changes in envelope gps protruding from viral mem, inducing fusion of viral mem w/mem of endosome -\> release of viral nucleocapsids into cell cytoplasm (**virus uncoating**)
- Viral RNA-dependent RNA polymerase (**RdRP**), assoc w/nucleocapsids, transcribes (+) sense mRNAs with 5’-caps and 3’ poly A, resembling host mRNAs
- _Host ribosomes translate viral proteins from these virus-specific mRNAs_
- Viral RdRP also replicates viral (-) sense genome by making a (+) sense cRNA intermediate used as template to make new (-) sense genomes (or vRNAs) -\> (-) sense genomes assembled, virus particles released **budding**
38
How is EBV linked to nasopharyngeal carcinoma?
- Nasopharyngeal carcinoma is a neoplasm of epithelial cells associated with EBV worldwide
- High frequency in **southern China: high salt diet** likely cofactor
- _Initial presentation_: painless **lump in the neck**
- At best, only 60% of patients survive ten years
39
What other 2 B-cell abnormalities are caused by EBV (not KS)?
- _Primary effusion lymphoma_
1. Non-Hodgkin’s B-cell lymphoma
2. Commonly found in _body cavities_
3. Mean survival time 2-6 months
4. KSHV in virtually all tumors of HIV+ patients
- _Multicentric Castleman’s disease_
1. _Lymph node tumors_, not strictly a cancer
2. KSHV in virtually all tumors of HIV+ patients
40
How do you prevent dengue infection?
- Only way to prevent dengue virus acquisition to avoid being bitten by a vector mosquito
- **No vaccine** for dengue virus available, but _tetravalent (for all four serotypes) vaccine is being produced_ by Sanofi-Pasteur which has undergone initial safety and efficacy testing
