Human and animal influenzas: forced coexistence

Torres-Lana A

Influenza is a fascinating topic because of the nature of the causative agent and its

presentation in the form of annual endemic cycles, epidemic outbreaks, and pandemics

with great impact on public health due to direct morbidity and mortality or to the

aggravation of other underlying diseases. Different variants of the influenza virus emerge

every 1 to 2 years as the result of point mutations (antigenic drift) or major genetic

reassortment (antigenic shift), which involves mixing animal and human viruses. These

characteristics oblige the establishment of worldwide early warning systems so that the

location of each new variant can be ascertained. The emergence of avian influenza

viruses H5N1 and recently of the swine influenza virus H1N1 compel us to study the

pathogenic mechanisms of these viruses and their propagation between animal species

as well as to determine how the interspecies barrier is broken. A variety of clinical

pictures are associated with influenzas of animal origin and in general an etiologic

diagnosis is not obtained. However, such a diagnosis must be taken into consideration

when the results will affect clinical, therapeutic, and epidemiologic decisions. Multiple

approaches will be required if we are to cope with a future influenza pandemic, which

will probably come from an animal source. Epidemiologic surveillance, antiviral therapy,

vaccinations, and non-pharmacologic measures all become important public health tools

for containing the impact of the virus on society as a whole and avoiding sustained

transmission.

Torres-Lana A