What are the characteristic features and symptoms of the influenza A virus?

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Influenza, one of the most common infectious diseases, is a highly contagious airborne disease that occurs in seasonal epidemics and manifests as an acute febrile illness with variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. Influenza virus is an orthomyxovirus—an enveloped, segmented, negative-sense RNA (ribonucleic acid) virus. Influenza virus has three strains—A, B, and C. Avian influenza is caused by influenza A virus, which has eight RNA segments. The serotypes of influenza A virus are identified based on the hemagglutinin (H) and neuraminidase (N) proteins; 16 H serotypes and nine N serotypes have been identified. For example, one currently circulating strain is designated as H3N2. The strain previously considered the greatest threat was H5N1, mostly because of the high associated mortality rate (up to 60%) in infected humans. H5N1 infections have decreased substantially in recent years, and the most recent avian influenza of note is H7N9, first described in China in 2013.

Although all strains of influenza A virus naturally infect birds, certain strains can infect mammalian hosts such as pigs and humans. Some common signs and symptoms of influenza are fever, sore throat, myalgias, frontal or retro-orbital (behind the eyes) headache, nasal discharge, weakness, severe fatigue, cough, and other respiratory symptoms, tachycardia (an increased heart rate), and red watery eyes.

The gold standard for diagnosing influenza A and B is a viral culture of nasopharyngeal (nose and pharynx) samples or throat samples. In elderly or high-risk patients with pulmonary symptoms, chest radiography is also done to exclude pneumonia (a condition where the air sacs of the lungs get inflamed), one of the complications of influenza.

No vaccine is currently available to the public for routine immunization, although two adjuvanted influenza A (H5N1) monovalent vaccines have been approved by the FDA (The United States Food and Drug Administration) for H5N1 influenza A. Each vaccine is approved for patients aged six months or older and is administered as a two-dose series given at least 21 days apart. Prophylactic antivirals are not indicated for patients who plan to travel to areas where avian influenza has been reported. Travelers who plan to travel to areas of the world affected by avian influenza outbreaks in birds or humans are advised to avoid close contact with poultry, especially diseased or dead birds, and to consume only adequately cooked meat. If contact with birds in enclosed spaces is unavoidable, an N-95 respirator mask (or equivalent), gloves, and goggles should be used to minimize contact with droplets or particulates. Other than this, you can always contact your nearby community clinic for more information and other guidance.

I hope this information helps provide some insight into your symptoms.

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