Passage:Influenza

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Originally thought to be caused by the Gram-negative bacillus bacteria, Haemophilus influenzae, it is now known that influenza pandemics are actually the result of an RNA virus from the family Orthomyxoviridae.


Commonly referred to as the flu, Influenza is an infectious disease with types living in a wide variety of birds and mammals. Specifically, in humans, influenza causes fever, sore throat, muscle pains, and in severe cases, death.


There are three types of influenza virus: Influenzavirus A, Influenzavirus B, and Influenzavirus C. Influenza A and C infect multiple species, while influenza B almost exclusively infects humans. The type A viruses are the most virulent human pathogens among the three influenza types and cause the most severe disease. Occasionally viruses are transmitted between species which may then lead to devastating outbreaks in domestic poultry or give rise to human influenza pandemics.


The influenza A virus particle is 80–120 nm in diameter and usually roughly spherical, although filamentous forms can occur. Unusual for a virus, the influenza A genome is not a single piece of nucleic acid; instead, it contains eight pieces of segmented negative-sense RNA, which encode 11 proteins.


Neuraminidase is an enzyme involved in the release of progeny virus from infected cells, by cleaving sugars that bind the mature viral particles. By contrast, hemagglutinin is a sugar binding protein, or lectin, that mediates binding of the virus to target cells and entry of the viral genome into the target cell. The matrix protein (M1) is the most abundant structural protein of the influenza A virus. M1 forms a protein layer beneath the viral envelope. Nucleoprotein NP constitutes the protein backbone of the ribonucleoproteins (RNPs), a unique formation of protein and RNA bound tightly. During the late stages of infection, RNPs must be exported from the nucleus to the cytoplasm and is controlled by the nuclear export protein, or simply NEP. In the cytoplasm, M1 protein surrounds newly replicated RNPs forming complexes with the eight different segments. These progeny virion particles are then pushed through the plasma membrane thus retaining a lipid bilayer coat.


Influenzavirus A can undergo both antigenic shift and antigenic drift. Antigenic drift is the natural process of mutation resulting in small changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. Antigenic shift however, like sexual reproduction, allows the viral chromosomes, or segments, to be redistributed to form unique combinations when two viruses infect one cell.


1. The shape of the bacteria Haemophilus influenzae is considered to be?

rod like
→ The passage states that H. influenzae is a bacillus, from this one can infer that it must have a rod-like shape.
helical
→ spirillum is the term for a spiral or helix shaped baceria.
spherical
→ coccus is the term for a spherical shaped baceria.
dentritic
→ dentritic shape cells have many small tentacle-like pillars of cell membrane, however they are only seen in advanced eukaryotes (T-cells in humans for examples).

2. The success of Influenza A can be attributed to all of the following except:

A diverse host pool
→ This is true, a large pool of hosts provides greater room for mutation and replication
Genetic shift
→ This is true, genetic shift, or mutation, allows Influenza to continue to adapt and escape vaccine and human immune memory.
Proteins to evade the immune system
→ Influenza does not have any proteins or enzymes capable of blocking or suppressing the immune system directly. Once someone is infected with influenza they can develop immunity to that strain easily.
Genetic drift
→ This is true, the ability to recombine with other influenza strains to produce new unique combinations is a rapid way to develop novel and unique strains.

3. In comparing genetic shift to meiosis, which statement is false?

Genetic shift requires two viral particles to infect one cell while meiosis requires two gametes to combine.
Both genetic shift and meiosis allow for chromosomal or segment cross-over of genetic material.
→ The passage does not state that crossing-over occurs between fragments like meiosis does between chromosomes.
Both genetic shift and meiosis can result in more successful progeny.
→ Sexual reproduction allows for a greater chance to produce favourable combinations of genes, the resulting progeny may thus be more successful.
Genetic shift happens randomly during viral packaging while meiosis is controlled by host proteins.
→ This is true, genetic shift is simply a reassortment of the different viral RNPs and occurs randomly during the packing of progeny.

4. The method by which the virion progeny exit the infected host cell is similar to which biological process?

pinocytosis
→ Pinocytosis is a form of endocytosis in which small particles are brought into the cell.
exocytosis
→ Exocytosis is the only process here which involves the release of internal cellular components. In this case the viral progeny are taking advantage of the process to both gain a protective lipid coat and to be released.
endocytosis
→ Endocytosis is a process where cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane.
phagocytosis
→ Phagocytosis is the process by which cells ingest large objects, such as cells and viral particles.

5. Which of the following is not a trait shared by both Influenza and prokaryotes?

Genetic material.
→ Influenza uses RNA to carry genetic information while prokaryotes use DNA.
Ribosomes
→ Ribosomes are used to translate mRNA into protein. Cells have these components, however viruses do not, instead they use their host's ribosomes.
A template dependent polymerase
→ All cells have polymerases as do any viruses which carries RNA. Most viruses (specifically RNA viruses without exception) encode their own polymerase capable of replicating their RNA since host polymerases cannot perform the necessary replication of RNA into RNA (or DNA in the case of retroviruses).
An envelope
→ Both prokaryotes and Influenza have a lipid envelope, however the coat of influenza is derived from its host cell membrane.

6. Which of the following Influenza proteins is most likely to cause an immune response?

Matrix Protein (M1)
Nuclear Export Protein (NEP)
Nucleoprotein (NP)
Hemagglutinin (HA)
→ Only hemagglutinin and neuraminidase are present on the surface of an Influenza virion, thus these are the most likely targets for antibody recognition.

7. A scientist discovers that an avian strain of Influenza is capable of infecting most humans except some poultry workers in rural towns, which of the following is most likely true?

HA is capable of binding human glycoproteins but not avian glycoproteins on target host cells.
→ This is false. It is most likely that this strain is capable of binding both types hence its ability to be transfered from birds to humans.
Most humans previously exposed to this strain retain immunity.
→ The most likely explanation of why the poultry workers are not infected is because they have already been exposed to minor strains of similar Avian Influenzas during their work with poultry while the general public has not.
Some humans have genetic mutations conferring resistance to this avian strain in question.
→ This is false. The likely hood of all the poultry workers having resistance due to a genetic mutation would be very small if not impossible.
This strain is lethal to immunocompromised individuals.
→ The question does not state that either group of humans is immunocompromised in anyway but if anything, the poultry workers would be in worse health conditions than the general public and thus they would be the ones to get sick if this were true.

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