Question

The influenza virus H1N1 can infect both humans and other animals. Use the Internet to collect information that allows you to describe some of the similarities and some of the differences between the H1N1 virus and the virus responsible for avian influenza. (See the Chemistry in Action "Influenza: Variations on a Theme," p. 832.)

Short answer

H1N1 and avian influenza are both RNA viruses causing respiratory illness but differ in host range and symptom severity. H1N1 affects humans and pigs worldwide, whereas avian flu mainly affects birds and causes severe human illness rarely.

Step-by-step solution

Introduction to H1N1 and Avian Influenza

The H1N1 virus, also known as the swine flu, primarily infects humans and pigs, while avian influenza, commonly known as bird flu, primarily affects birds but can sometimes spread to humans and other animals. Both are types of influenza viruses that belong to the Orthomyxoviridae family.

Similarities

The H1N1 virus and the virus responsible for avian influenza share some commonalities. Both are RNA viruses with segmented genomes, which means their genetic materials are divided into separate sections. They undergo frequent genetic changes due to 'antigenic drift' and 'antigenic shift', allowing them to adapt to new hosts and environments. Both viruses cause respiratory symptoms in infected individuals.

Differences in Hosts and Transmission

H1N1 is a strain that has adapted to infect humans and pigs, facilitating transmission between these species. In contrast, the avian influenza virus mainly affects birds and occasionally transmits to humans, under specific conditions, often leading to severe disease.

Differences in Symptoms Severity

H1N1 infection in humans can range from mild to severe but generally causes symptoms similar to seasonal flu, such as fever and cough. In contrast, avian influenza in humans is often more severe, with a higher mortality rate, causing respiratory distress and multi-organ failure.

Differences in Geographical Spread

H1N1 has caused global pandemics, such as the 2009 pandemic, transmitting efficiently among humans worldwide. Avian influenza outbreaks are often restricted to specific regions, typically in Asia, where there is close contact between humans and birds.

Key concepts

RNA viruses

RNA viruses are viruses that use RNA, rather than DNA, as their genetic material. This characteristic makes them unique in the world of microbiology. Since RNA is single-stranded, it is generally more prone to mutations than double-stranded DNA. This makes RNA viruses particularly adaptable to changing environments and helps them jump between different species.
Let's break it down a bit more:

• **Single-Stranded RNA**: Most RNA viruses, including the influenza viruses, have single-stranded RNA, which is less stable than double-stranded DNA.
• **Mutations**: Because RNA polymerase, the enzyme that replicates RNA, does not proofread well, RNA viruses can mutate quickly. This allows them to evolve rapidly.
• **Genetic Segmentation**: The genomes of influenza viruses are segmented. This segmentation allows for the swapping of genetic material between virus strains, which is a process known as reassortment. It can make these viruses incredibly variable.

Genetic changes

Genetic changes in viruses can be quite profound, leading to significant impacts on how these viruses behave and spread. In the case of RNA viruses like H1N1 and avian influenza, genetic changes occur frequently due to two main processes: antigenic drift and antigenic shift.
Here's how these processes work:

• **Antigenic Drift**: This is a slow and steady process. Small mutations accumulate over time as the virus replicates. These minor changes can eventually lead to new virus strains that the immune system might not recognize, contributing to seasonal flu outbreaks.
• **Antigenic Shift**: A more dramatic and sudden change. It occurs when two different strains of a virus infect the same cell and exchange genetic material. This can lead to the creation of a new virus with different surface proteins. Antigenic shift is responsible for pandemics because the human population has little to no pre-existing immunity against the new strain.

Orthomyxoviridae

Orthomyxoviridae is a family of viruses that very much requires attention. This family includes the influenza viruses, which are particularly notorious for causing respiratory illnesses.
Let's delve a little deeper into the features of Orthomyxoviridae:

• **Members**: This virus family includes influenza A, B, C, and D viruses, with influenza A and B being the most common among humans.
• **Segmented Genome**: Each member of this family has a segmented RNA genome. Usually eight segments. This feature allows for reassortment, leading to new virus subtypes.
• **Host Range**: Influenza A, in particular, has a wide host range, including humans, birds, and other mammals. This host diversity helps these viruses evolve through genetic changes and adapt to different environments.
• **Influenza A Subtypes**: These are classified based on two surface proteins called hemagglutinin (H) and neuraminidase (N). H1N1, for example, belongs to this category due to these specific proteins.