Influenza

Prepared by

Dr Shaimaa baher

Disease definition

• Influenza, both Type A and Type B, commonly referred to as the "flu", manifests itself in susceptible humans with cold-like symptoms aggravated by fever, malaise, muscle and joint aches, nausea and vomiting.  Immune-compromised, the young, and the elderly are particularly susceptible if unprotected.

Agent causing Influenza

Influenza viruses are of the Orthomyxoviridae family and have three types:

• type A (found in both humans and animals)
• type B (found only in humans)
• type C (uncommon strain found only in humans). 

• Type A may be sub-typed by two surface glycoprotein into 144 different subtypes.  [There are 16 H or hemagglutinins and 9 N or neuraminidases, allowing 144 different subtypes combinations]. 

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• For the human, type A carries a more threatening risk due to the assortment of virus components. 

Antigenic shift/ antigenic drift

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Influenza virus is unique among viruses because it is frequently subject to antigenic variation, both major and minor. When there is a sudden complete or major change it is called antigenic shift and when the antigen change is gradual over a period of time it is called Drift.

• Antigenic shift is the process by which two different strains of influenza combine to form a new subtype having a mixture of the surface antigens of the two original strains. Because the human immune system has difficulty recognizing the new influenza strain, it may be highly dangerous.

• Antigenic drift which is the natural mutation over time of known strains of influenza (or other things, in a more general sense) to avoid the immune system. Antigenic drift occurs in all types of influenza including influenza A, B and C.

• antigenic shift, however, occurs only in influenza A because it infects more than just humans. Affected species include other mammals and birds, giving influenza A the opportunity for a major reorganization of surface antigens. Influenza B and C only infect humans, minimizing the chance to mutate drastically.

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• In 2004, scientists pointed out that the avian influenza virus might undergo an antigenic shift with the human flu virus and cause a global influenza pandemic like the one in 1918.

Influenza reservoirs

• Animals and birds: wide variety of animals and birds “swine – horses-dogs-cats-domestic poultry and wild aquatic birds.

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• There is increasing evidence that the animal reservoirs provide new strains by recombination between human, animals and birds.

Source of infection:

• Man is the main source of infection as a clinical /subclinical case. During epidemics a large number of mild and asymptomatic infection occur, which play an important role in spread of infection. Human carriers of avian flu H5N1 and Swine flu H1N1 A was recently reported by the World Health organization.

• Aquatic birds are the reservoirs of all subtypes of influenza A viruses. In wild ducks, influenza viruses replicate in the cells lining the intestinal tract, cause no disease signs, and are excreted in high concentrations in the faeces.
• Avian influenza viruses have been isolated from freshly deposited faecal material and from lake water, which indicates that waterfowl have a very efficient way to transmit viruses, i.e., by faecal material in the water supply.

Modes of transmission

• Influenza spreads mainly by droplet infection (direct / indirect) during forcible respiratory acts; droplets can infect others 3 – 5 meters apart.
• Contaminated hand by the virus (respiratory discharge of case or faecal matters of poultry or infected animal excreta, can inoculate the virus to nasal or conjunctiva mucosa)

• Although it is unusual for people to get influenza virus infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza viruses have been reported. These sporadic human infections and outbreaks, however, rarely result in sustained transmission among humans

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Period of Communicability

• 1-2 days before onset of signs and symptoms (incubatory carriers), and after appearance of symptoms, up to maximum 10 days.

Exit route from source:

• Respiratory systems, nose, mouth with nasopharyngeal secretions in human flu
• With faces of infected wild and domestic birds in avian flu
• Respiratory discharge of pigs in swine flu.

Host resistance:

• In general young children, pregnant and immune-compromised person are at high risk, in addition people with respiratory problems and mal-nutrition.

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• The greatest risk factor for bird flu seems to be contact with sick birds or with surfaces contaminated by their feathers, saliva or droppings. The World Health Organization (WHO) has confirmed human-to-human transmission of bird flu. infected birds or associated material presents the greatest hazard.

• Seasonality epidemics usually occurs in winter months in the Northern Hemisphere and in winter or rainy season in Southern one
• Incubation period: 1-3 days

Clinical presentation:

• Fever (usually high), Headache, Muscle aches, Chills, Extreme tiredness, Dry cough, Runny nose may also occur but is more common in children than adults, Stomach symptoms, such as nausea, vomiting, and diarrhoea, may also occur but are more common in children than adults.

Complications:

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• Complications of flu can include bacterial pneumonia (suspected if fever persists more than 4-5 days or recurs after convalescence), ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Young children may get convulsions (fever) or croups.

Avian Influenza (Bird flu)�

• A highly pathogenic epizootic disease has crossed the species barrier in Asia, Africa and Europe to cause many human fatalities and a pandemic threat. All birds are thought to be susceptible to infection with avian influenza viruses. Many wild bird species like waterfowl carry these viruses with no apparent signs of harm. Many pandemics had occurred in the last century and the current pandemic began in December 2003.

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• Influenza virus A is the cause of all flu pandemics and infect humans and other mammals and birds.
• The current pandemic is caused by subtype H5 N1.
• The virus survives in low temperature and water but killed at 70C, by alcohol, vinegar and normal disinfectants.
• Birds (wild, domestic) and pigs are the sources of infection. The virus finds exit in nasopharyngeal discharges, lacrimal discharges and stool.

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• The main method of spread to humans is direct contact with infected poultry, its discharges and feces. I.P. internationally 7 days.
• Symptoms in humans include high fever, influenza-like symptoms together with diarrhea, vomiting, abdominal pain, and bleeding from the nose and gums.

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• In Egypt and globally, the general case fatality rate reached 50% mostly due to respiratory complications.
• Live attenuated vaccines are available at present to be given for poultry. They are well tolerated and protective to animals preventing mortality but not affecting the carrier state.
• Tamiflu is the antiviral drug of choice in treating avian flu.

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Swine flu�

• It is a respiratory disease of pigs caused by type A influenza viruses (H1N1 subtype) that causes regular outbreaks in pigs. People do not normally get swine flu, but human infections can and do happen. Spread of this swine influenza A (H1N1) virus is thought to be happening in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing of people with influenza. Sometimes, people may become infected by touching something with flu viruses on it and then touching their mouth or nose.

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• The symptoms of swine flu in people are similar to the symptoms of regular human flu. Some people have reported also diarrhea and vomiting. Infected people may be able to infect others beginning 1 day before symptoms develop and up to 7 or more days after becoming sick. This means that you may be able to pass the flu to someone else before you know you are sick.

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• Prevention:
• General measures: First and most important: wash your hands. Avoid touching your eyes, nose or mouth, germs spread this way. Try not to touch surfaces that may be contaminated with the flu virus. Avoid also contact with people who are sick, besides other general measures for preventing respiratory infections.

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Other Safety precautions:

• Culling- killing large numbers of infected and potentially infected animals
• Quarantine- putting infected farms in quarantine.
• Avoid live animal markets, poultry and big farms in infected countries.
• Although swine flu viruses do not infect orally, you have to cool pork thoroughly.

Specific measures: a recently developed vaccine given for at risk groups e.g. pilgrims.

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International measures: The WHO does not recommend any travel restrictions to areas experiencing outbreaks, including countries, which have reported, associated cases of human infection. Nonetheless, thermal screening for international travelers is conducted at the airports before entering the country.

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Control of Influenza:

• Good ventilation of public buildings –the avoidance of crowded places during epidemics.
• encouraging people to cover their faces with a handkerchief when coughing and sneezing – to stay at home at first sign of influenza…

Prevention: [General – Specific]�

• I. General personal cleanness and healthy habits such as
• keeping hands ( disinfectants
• clean kitchen and bathroom surfaces
• avoid contaminating commonly used objects at home or work environment healthy habits and use of tissue papers during sneezing and coughing...

II. Specific (Seasonal Flu Vaccines)

Killed vaccine “flu shot" is an inactivated vaccine (containing killed virus) that is given subcutaneous or intramuscular (0.5 ml) to those above 3 years and 0.25 ml for infant 6 -36 months of age. Fever, local inflammation. Not to be given to person allergic to egg protein.

• The nasal-spray flu vaccine (sometimes referred to as LAIV for Live Attenuated Influenza Vaccine or Flu-Mist®), was approved in 2003. The nasal-spray flu vaccine contains attenuated (weakened) live viruses, and is administered by nasal sprayer. It is approved for use only among healthy people 2-49 years of age who are not pregnant.

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• Split virus vaccine “lower antigenicity – several injections – recommended for children.

• Neuraminidase – specific vaccine (N antigen only): it reduces both the amount of the virus replication in the respiratory tract and the ability to transmit virus to contact – reduce clinical symptoms in infected person and permit subclinical infection that may gives lasting immunity.
• Recombinant vaccine under trial.

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