Unit 3 - Poxviruses Flashcards

Question

What is the broad host range of poxviruese?

Answer 1

* Infect _many_ species * Most poxviruses named after the animal from which they were origninally isolated (e.g. cowpox, camelpox)

Answer 2

* Rabbits were an invasive species of Australia. * The rabbits bred rapidly and caused massive agricultural and environmental damage. * Myxoma virus was introduced to control the population.

Answer 3

With the exception of variola and MCV ... All poxvirus infections of humans today are zoonoses

Answer 4

* Vaccinia is the **prototype** of poxviruses. * Grows in a wide host range of cells in culture (e.g., monkey, rabbit, human, hamster, mouse, etc.) * Within 12–24 hours, it can be grown in high titers. 200 bp genome, linear, dsDNA 200 genes Ends contain ITRs * Ends of the genome contain unessential genes * More than 40 different poxvirus genomes have been sequenced.

Answer 5

* 90 essential genes are highly conserved among poxviruses * Viral Replication and morphogenesis.

Answer 6

* Two forms of virus particles in cell culture: * Extracellular enveloped virion (**EEV)** contains two membranes (Golgi and plasma membrane) * Intracellular mature virion (**IMV)** contains one membrane (derived from Golgi) * IMVs are released upon cell lysis. * Each infectious form is thought to enter cells by different mechanisms.

Answer 7

No specific host-cell receptors have been identified. * Some studies have shown that the A27L virion protein of vaccinia interacts with cell surface glycosaminoglycans (GAGs). * GAGs are ubiquitously expressed on many different cell surfaces. During uncoating, the outer membrane of EEV is removed and the particle enters the cell, where it loses the second membrane and the viral core passes into the cytoplasm.

Answer 8

Unique hallmark of vaccinia/poxviruses: * Acquired all functions necessary for genome replication in the cytoplasm * All other dsDNA viruses replicate genomes in the nucleus Gene expression **(transcription**) is sequential. Three classes of mRNAs * Early (30 min post-infection) * Intermediate(100 min post-infection) * Late (140 min to 48 hrs posr-infection)

Answer 9

Vaccinia virus particle contains transcriptional machinery capable of synthesizing viral mRNAs that are recognized by the cell’s translational machinery. * DNA dependent RNA polymerase * Transcription factor (VETF) * Capping enzymes * Methylating enzymes * Poly(A) polymerase * D10 decapping enzyme involved in mRNA turnover

Answer 10

* Early mRNAs encode enzymes and factors need for transcription of the intermediate class of mRNAs. * Intermediate mRNAs encode enzymes and factors required for late gene expression. * Late mRNAs expression occurs after DNA replication. Encodes factors and enzymes packaged into the virion Structural proteins

Answer 11

* After the late gene products are synthesized, infectious particles are assembled. * Assembly involves interactions with the cytoskeleton (e.g., actin-binding proteins and microtubules). * The particles are wrapped with a Golgi-derived membrane and transported to the periphery of the cell. * EEV picks up an additional plasma membrane as it is released outside of the cell. * EEVs can initiate infection (cell-to-cell spread)

Answer 12

Poxviruses produce viroceptors and virokines. Viroceptors are altered cellular receptors that have lost their transmembrane anchor sequences. * Secreted from infected cells * Sequester ligands onto the receptor portion of the protein (“cytokine sponges”) Virokines resemble host cytokines. * Secreted like cytokines

Answer 13

* Secreted complement regulatory proteins * Secreted proteins that bind to interferons * Secreted interleukin-18 binding proteins * Secreted tumor necrosis factor homologs (apoptosis inhibitors) * Serine protease inhibitors (apoptosis inhibition) * Intracellular inhibitors of PKR (interferon pathway) * No one specific poxvirus uses all of these collective immune evasion strategies; all seek to target the innate immune response.

Answer 14

1965–1966 study by Vogel and Chakravartii * Compared 415 unvaccinated Indian smallpox survivors and victims * Persons with Blood Type A were **7×** more likely to contract smallpox. * Persons with Blood Type A were **3×** more likely to develop a severe case. * Persons with Blood Type A were **2×** more likely to die of it. 2003 study by Galvani and Slatkin Selective pressure by smallpox resulted in CCR5-32 resistance allele. Fortuitously, this resistance allele also protects individuals from HIV-1 infection.

Answer 15

Smallpox vaccine history * Late 17th century in China Inhale or plug nose with powdered smallpox scabs Put underwear of an infected child on a healthy child for several days * Variolation practiced by Hindus in India during 16th century. Intentional inoculation of dried smallpox scabs into the skin of uninfected individuals, causing a mild form of the disease and immunity upon exposure to variola.

Answer 16

Practice spread from central Asia, to east China, west to Africa and the Ottoman Empire * 2%–3% of variolated people died from ordinary smallpox infections (compared to 30% mortality) Lady Mary Wortley Montague, wife of British Ambassador, observed variolation during travels to Istanbul in 1717. * Asked Embassy surgeon Charles Maitland to engraft her 4-year- old daughter in 1721 * Maitland did a study; variolated six prisoners * Prisoners survived after exposure to children infected with smallpox. * They had a milder form of the disease and developed immunity. * Royal Society of London found the practice acceptable and people were variolated in England.

Answer 17

* Physician in England, credited with cowpox vaccination * Experimented with the folklore that milkmaids who contracted cowpox “did not take the smallpox.” * In 1796, Jenner variolated the 8-year-old son of a local farmer with fluid from the cowpox pustules from the hand of a local dairymaid. * A few months later, the boy was injected with smallpox and failed to develop the disease.

Answer 18

* Jenner published his work. * Immediate reaction to work was ridicule. * Clergy claimed it repulsive and ungodly to inoculate someone with material from a diseased animal. * Jenner’s work later accepted and the word vaccination was coined. * Vaccinia virus eventually replaced the smallpox virus for vaccination

Answer 19

* Fluid or lymph removed from a vesicle or pustule of a previously vaccinated person was passaged arm-to-arm between humans. * Strain was lost occasionally and further strains obtained from cows or horses. * Not a safe practice! * Vaccine became contaminated with variola major or minor. * Way to spread other infectious diseases (e.g., hepatitis B) * Arm-to-arm passage banned in 1898

Answer 20

* These early vaccines were crude and contaminated with cell and bacterial debris. * Over time, protocols became standardized. * Vaccines were tested for specific pathogens. * 1967 WHO recommended seed lot containing Liser or New York City Board of Health strain (NYBOH) grown by Wyeth Laboratories for vaccine production.

Answer 21

* Variola has a narrow host range. * There are no carriers. * There are no animal reservoirs. * A highly effective and inexpensive freeze-dried vaccine was available. * Surveillance of the disease was easy (centrifugal rash). * The WHO created a program to eradicate it.

Answer 22

**1950:** hemisphere-effort by Pan American Health Organization to eliminate smallpox **1967:** WHO launches plan to eradicate smallpox through mass vaccination. * 50 million cases of smallpox worldwide in the early 1950s * Each outbreak had to be stopped from spreading via isolation of cases and vaccination of surrounding individuals (“ring vaccination”) * Initial problem with inadequate reporting Over time, goal changed to containment vaccination or surveillance vaccination around newly discovered cases or outbreaks. * This strategy evolved after countries like Nigeria and India experienced outbreaks in regions where religious groups refused vaccination. Use of smallpox recognition cards, containment books, rewards, rumor registers to increase success of surveillance and containment efforts * 100 rupees ($12) in 1974 * 1,000 rupees ($125) in 1975 * $1,000 in Bangladesh and Somalia in 1978

Answer 23

* Mass smallpox vaccination was stopped in 1972. * U.S. current stockpile consists of * New cell culture-derived ACAM2000 vaccine * ACAM2000 replacing Dryvax stockpile * European Union and WHO vaccines produced from calf lymph * These vaccines have not been tested by modern methods for the presence of pathogens.

Answer 24

Who is vaccinated today? * Laboratory workers who work with poxviruses * Healthcare workers (volunteer compliance) * Members of the military Dryvax vaccine * Cultured in the skin of calves, freeze-dried * Mixed population of vaccinia strains Bifurcated needle, deltoid of arm * Primary inoculation—3 pricks * Secondary inoculation—15 pricks

Answer 25

* Based on 1960s statistics, 1,000 of every 1 million vaccinees have a serious reaction to the vaccine (**0.1%).** * Serious side effects occur in individuals * with skin conditions such as eczema and atopic dermatitis * with weakened immune systems * with other his risk factors such as high blood pressure, diabetes, and high cholesterol * Safer vaccines are needed in case of bioterrorism event that would require mass-vaccination.

Answer 26

* Smallpox vaccine has been discontinued: no herd immunity to smallpox and monkeypox. * No licensed FDA drug to treat smallpox infections. * Cidofovir has been used to treat AIDS patients with MCV infections. * Target viral genes involved in DNA replication, mRNA synthesis, protein modification, and assembly

Answer 27

* All smallpox research must be performed in BSL-4 laboratories. * 2005 Intelligence Reform and Terrorism Prevention Act bans synthesis of variola virus from scratch. * Does not prohibit researchers from engineering similar poxviruses to contain variola genes. * May 2011: Smallpox gets stay of execution * 27–7 vote WHO delayed destroying smallpox stockpiles located in the U.S. and Russia * 3-5 more years for researchers to study the virus before voting again to keep or destroy stockpiles

Answer 28

* Use of variola as a biological weapon has a long history. * Variola as germ warfare against Native American Indians in French and Indian Wars (1754–1763). * Following the Civil War, professional grave robber William Cunningham delivered a corpse of a recently buried smallpox victim to the anatomy dissecting room at the Medical College of Ohio, Cincinnati. Several students were infected.

Answer 29

* Useful vaccine vector due to their broad host range and ability to generate recombinant viruses that express a variety of foreign antigens * Large genome also for insertion of large foreign DNA fragments * Recombinant poxviruses to induce mucosal immune responses * E.g., rabies, * Potential use of attenuated Ankara VV strain, canarypox virus, and fowlpox virus for human vaccination

Answer 30

* 16,402 Thai citizens (60% male, 40% * female) enrolled * Canarypox vector-based candidate ALVAC-HIV * Recombinant gp120 protein based-vaccine * Six-year study * Reduced the risk of HIV infection by about 31%

Unit 3 - Poxviruses Flashcards

(54 cards)