<unk>  is caused by influenza A virus. Influenza belongs to the Orthomyxoviridae family. Influenza A is an enveloped, pleomorphic (spherical and filamentous forms) virus that contains a linear, segmented (8 segments), negative-sense, single-stranded RNA genome. The genome is composed of 8 segmented genes that encode 11 proteins. The World Health Organization (WHO) reports an incidence of 3 to 5 million cases of severe influenza disease annually, including 250,000 to 500,000 deaths every year. The majority of cases of<unk>  infection in humans have resulted from contact with infected poultry or contaminated environments. Human-to-human transmission is still rare and inefficient. Influenza virus is transmitted in aerosols of respiratory secretions. The hemagglutinin (HA) protein on the viral surface functions as a receptor binding site and binds to host receptors that contain sialic acid to allow viral fusion to the host cell in the respiratory tract, while the neuraminidase (NA) enzyme cleaves progeny virions from host cell receptors. Viral proteins are, at least in part, responsible for down-regulation of cytotoxic T-cell activity, evasion of immune responses, and activation of cytokines and pro-inflammatory mechanisms that contribute to host tissue injury. Classification of<unk>  may be based on either the pathogenicity of the virus (low pathogenicity vs. high pathogenicity) or the viral genetic subtypes (H5 vs. H7 vs. H9). Following exposure to the<unk>  virus, an incubation period of 2 to 3 days for H5N1 and 2 to 8 days for H7N9 precedes the onset of symptoms. The majority of patients present with with high-grade fever, cough, headache, sore throat, vomiting, diarrhea, and abdominal pain. Approximately 50% of patients with<unk>  develop severe complications such as acute respiratory distress syndrome, acute kidney injury, sepsis, and multiple organ dysfunction syndrome. Some strains of<unk>  virus are associated with a mortality rate as high as 60% of infected individuals. Patients without complicated disease usually recover within 3 to 5 days with no sequelae. Diagnostic tests available for<unk>  include viral culture, serology, rapid antigen testing, polymerase chain reaction (PCR), immunofluorescence assays, or other molecular assays.  Neuraminidase inhibitors can reduce the duration of viral replication and improve survival among patients with<unk> .  In cases of suspected<unk> , oseltamivir, zanamivir, or peramivir should be administered as soon possible, preferably within 48 hours of symptom-onset. Seasonal influenza (human influenza) vaccination will not prevent infection with<unk>  A viruses, but can reduce the risk of co-infection with human and<unk>  A viruses. The optimal way to prevent infection with<unk>  A viruses is to avoid sources of exposure, such as infected poultry, whenever possible.
Avian influenza
Swine influenza
Influenza
Freshers' Flu
Pertussis
COVID-19
Anthrax
Rubella