Table 1.

Characteristics of influenza viruses.

Characteristics	Influenza A	Influenza B	Influenza C	Influenza D
Virus structure	Enveloped Eight gene segments Hemagglutinin (HA) and neuraminidase (NA) glycoproteins		Enveloped Seven gene segments HA–esterase fusion glycoprotein
Epidemiology	Antigenic shift and drift	Only antigenic drift	Only antigenic drift	Only antigenic drift
Known hosts	Domestic and wild animals and avian species	Humans, pigs, and seals	Humans and pigs	Humans and livestock (cattle, pigs, and goats)
Clinical manifestation	Pandemic potential could cause high mortality	Can cause severe disease in elderly and high-risk populations	Mild seasonal disease predominantly in children	Mild disease in humans across ages
Available diagnostics	Rapid diagnostic tests (i.e., antigen detection); rapid molecular assays (nucleic acid detection); immunofluorescence; and cell culture		Real-time PCR and cell culture
Treatments	NA inhibitors: zanamivir, oseltamivir, and peramivir. Laninamivir investigational in USA.	NA inhibitors: zanamivir, oseltamivir, and peramivir. Laninamivir investigational in USA.	Supportive symptom management	Supportive symptom management
	Adamantanes: amantadine and rimantadine (notrecommended in USA due to resistance)