Background: Certain strains of influenza virus preferentially infect birds rather than humans. These viruses occur naturally in wild bird populations, particularly waterfowl, and can be spread to domestic birds. Like human influenza, avian influenza is highly contagious. The virus is shed in the saliva, nasal secretions, and feces of infected birds. Wild birds generally do not get sick from the infection, but some forms are highly pathogenic for domestic poultry and can be over 90% fatal. In 1997, one type of avian influenza strain A with surface proteins designated H5N1 (see the description of human influenza virus above) was found to be able to infect humans who came into contact with infected birds. Humans infected with avian influenza have a high mortality rate, but the virus does not seem to be able to spread from person to person. If the virus mutates such that it can spread more easily between people, it has the potential to cause a global pandemic, because it is different enough from the human influenza viruses that few people will have developed immunity from previous exposures.
Case A. An outbreak of avian influenza recently swept through several farms in a rural area outside Ho Chi Minh City, Viet Nam. The government has ordered that all farms in the area destroy their chickens to prevent the virus from spreading any further. World Health Organization (WHO) officials are collecting samples and testing them for influenza. The Vanh family’s farm is located just outside this area and they are hoping that they do not have to destroy their flock. But a few of their chickens have recently died, so the WHO workers take samples for testing. Their daughter, age 8, has a respiratory infection that the family worries may be related to the avian flu. WHO officials arrange for her to be tested for influenza, and recommend that other family members be tested even though they are not showing symptoms. Throat swab samples are taken from the father, mother, and two children (the sick daughter and her brother).
Procedure: To analyze this case, test the five samples of respiratory fluids from three of the dead chickens on the Vanh farm, and from the four family members, by ELISA for the presence of influenza H5N1 proteins. Then perform a 96-well PCR test on the cDNA isolated from the samples to see if influenza virus genetic material can be detected.
Samples for ELISA:
- Antibody for avian flu
- Protein: chicken 1
- Protein: chicken 2
- Protein: chicken 3
- Protein: daughter
- Protein: father
- Protein: mother
- Protein: son
- Protein: negative control
- Protein: positive control
Samples for 96-well PCR:
- Primers for avian flu
- DNA: chicken 1
- DNA: chicken 2
- DNA: chicken 3
- DNA: daughter
- DNA: father
- DNA: mother
- DNA: son
- DNA: negative control
- DNA: positive control
- Did the Vanh’s chickens die from influenza infection?
- Should the rest of their chickens be destroyed? What are the alternatives?
- Is the Vanh’s daughter infected with avian flu? What are the options for treating her illness?
- Do any other family members appear to be infected?
- What can be done to reduce the risk of avian influenza infection?
Case B. Turkey was one of the first European countries to report avian flu H5N1 infections in domestic poultry. Dozens of birds have died from the infection, and thousands more have been destroyed in order to stopped the spread of the virus. Several people in the same regions have come down with serious respiratory infections, and two people have died. Two of the patients are sisters in a family whose chickens tested positive for H5N1 influenza. Local health official want to test the two girls to see if their illness is caused by influenza H5N1 infection. The also want to test the rest of the family members, so throat swabs samples are taken from the mother, father and brother in addition the two girls. The family is adamant that only the older sister had direct contact with sick chickens so they do not understand why both girls would be ill if this virus was causing the symptoms.
Procedure: To analyze this case, run an ELISA to test the throat swab samples from each of the family members for the presence of influenza H5N1 proteins. Then test cDNA isolated from each sample for influenza genetic material using 96-well PCR.
Protein and DNA samples:
- brother
- father
- mother
- younger sister
- older sister
- negative control
- positive control
- Are the two sisters infected with avian influenza?
- Do any of the other family members appear to be infected?
- What are the implications if the second sister was infected without having had direct contact with infected chickens? How else might she have become infected?
- Is it possible to determine whether the two children were infected from the same source?
- What is the risk to the other family members?
- What can be done to reduce the further spread of the virus?