Influenza B[edit]
Main article: Influenza B virus
Host range of influenza viruses
Influenza B virus is almost exclusively a human pathogen, and is less common than influenza A. The only other animal known to be susceptible to influenza B infection is the seal.[47] This type of influenza mutates at a rate 2–3 times lower than type A[48] and consequently is less genetically diverse, with only one influenza B serotype.[26] As a result of this lack of antigenic diversity, a degree of immunity to influenza B is usually acquired at an early age. However, influenza B mutates enough that lasting immunity is not possible.[49] This reduced rate of antigenic change, combined with its limited host range (inhibiting cross species antigenic shift), ensures that pandemics of influenza B do not occur.[50]
Influenza C[edit]
Main article: Influenza C virus
The influenza C virus infects humans and pigs, and can cause severe illness and local epidemics.[51] However, influenza C is less common than the other types and usually causes mild disease in children.[52][53]
Influenza D[edit]
Main article: Influenza D virus
This is a genus that was classified in 2016, the members of which were first isolated in 2011.[54] This genus appears to be most closely related to Influenza C, from which it diverged several hundred years ago.[55] There are at least two extant strains of this genus.[56] The main hosts appear to be cattle, but the virus has been known to infect pigs as well.
Viability and disinfection[edit]
Mammalian influenza viruses tend to be labile, but can survive several hours in mucus.[57] Avian influenza virus can survive for 100 days in distilled water at room temperature, and 200 days at 17 °C (63 °F). The avian virus is inactivated more quickly in manure, but can survive for up to two weeks in feces on cages. Avian influenza viruses can survive indefinitely when frozen.[57] Influenza viruses are susceptible to bleach, 70% ethanol, aldehydes, oxidizing agents, and quaternary ammonium compounds. They are inactivated by heat of 133 °F (56 °C) for minimum of 60 minutes, as well as by low pH <2.[57]
Vaccination and prophylaxis[edit]
Targets of anti-influenza agents that are licensed or under investigation
Vaccines and drugs are available for the prophylaxis and treatment of influenza virus infections. Vaccines are composed of either inactivated or live attenuated virions of the H1N1 and H3N2 human influenza A viruses, as well as those of influenza B viruses. Because the antigenicities of the wild viruses evolve, vaccines are reformulated annually by updating the seed strains.[citation needed]
When the antigenicities of the seed strains and wild viruses do not match, vaccines fail to protect the vaccinees.[citation needed] In addition, even when they do match, escape mutants are often generated.[citation needed]
Drugs available for the treatment of influenza include Amantadine and Rimantadine, which inhibit the uncoating of virions by interfering with M2, and Oseltamivir (marketed under the brand name Tamiflu), Zanamivir, and Peramivir, which inhibit the release of virions from infected cells by interfering with NA. However, escape mutants are often generated for the former drug and less frequently for the latter drug.[58]