Common Viral Pathogens VI

Question 1

Antigenic drift

Answer 1

refers to a gradual change in the virus that occurs through a slow series of mutations, substitutions or deletions in amino acids constituting the hemagglutinin or neuraminidase surface antigens. Occurring only after a particular viral strain has become established in humans, antigenic drift represents an adaptation to the development of host antibodies. Newly developed antigenic strains of influenza then prevail for a period of 2 to 5 years, only to be replaced by the next emerging strain

Question 2

Antigenic shift

Answer 2

when a type A influenza virus with a completely novel hemagglutinin or neuraminidase gene segment is introduced into humans. The new gene segment is usually acquired from other host species (i.e. birds or swine). Gene reassortment can occur when two or more influenza viruses infect a single human or animal. Because influenza has a segmented genome, some gene segments can be “swapped” between strains – producing a new virus that has gene segments from both viral strains. Pigs can act as “mixing vessels” because they can be infected with both human and avian strains. Antigenic shift is less likely but has more of an effect

Question 3

origin and basic epidemiology of H1N1

Answer 3

It was first noted in March and April 2009, when an outbreak of a new type of H1N1 influenza A virus infection was detected in Mexico, with human cases subsequently observed in many other countries including the United States and Canada. The virus was referred to as “swine flu” because laboratory testing showed that most of the virus’ gene segments were similar to influenza viruses that were known to circulate in pigs. We believe this virus strain was created from reassortment.

Question 4

morbidity/mortality of H1N1

Answer 4

In terms of the “swine influenza (Pandemic H1N1)” pandemic of 2009-2010, CDC estimates we had about 60 million cases, 270,000 related hospitalizations, and about 12,000 deaths. The 2009 H1N1 (pandemic swine influenza) strain rapidly became the dominant circulating influenza strain world-wide. On June 11, 2009, the World Health Organization raised its pandemic alert level to the highest level, indicating widespread community transmission of Pandemic H1N1 on at least two continents.

Question 5

Who does H1N1 affect most (age groups)?

Answer 5

The rate of Pandemic H1N1 infection in the United States, during the 2009-2010 season, was highest among children and young adults ≤24 years of age. Pandemic H1N1 influenza A infections were less common in persons older than 65 years.

Question 6

H5N1 - about and geographic occurance

Answer 6

Currently, there is a highly virulent strain, H5N1, circulating in some bird populations that can cause severe disease in wild birds, domesticated birds, and can occasionally be transmitted to humans. H5N1 has been dubbed “bird flu” by the news media and when we talk about “avian influenza” in humans it is the H5N1 strain that is implied. H5N1 has been responsible for outbreaks in domesticated poultry throughout SE Asia and in recent years there have been outbreaks in Mongolia, Russia, Eastern Europe (Turkey, Romania, Hungary) and Africa (Ghana, Toga). Transmission is through close contact with birds.

Question 7

H5N1 - importance to public health

Answer 7

Studies of the 1918 influenza pandemic, the largest pandemic in recorded history, have shown the hemagglutinin was from an avian strain and bound human receptors in the normal alpha 2, 6 configuration. This resulted in the ability of this “avian strain” to be transmitted efficiently human-to-human. Humans had no protection from this novel strain and it rapidly spread around the world killing 50 million people. This is precisely what scientists fear could happen with the current H5N1 avian strain.

Question 8

3 conditions must be met to declare a pandemic:

Answer 8

1) Emergence of a new influenza virus subtype
2) Virus must infect humans and cause serious illness
3) Virus must have sustained transmission and spread easily (continue without interruption) among humans

Question 9

6 stages of a pandemic

Answer 9

1. interpandemic phase
2. new virus in animals, no human cases
3. Pandemic alert (no/very limited human-human transmission)
4. New virus causes human cases (increased)
5. New virus causes human cases (significant)
6. Pandemic (efficient and sufficient human-human transmission)