Dr Saima Hasan
INFLUENZA infection is highly contagious mild to severe respiratory illness of birds, animals and humans caused by influenza viruses. According to recent estimates of World Health Organisation (WHO) influenza viruses (IAVs) cause recurrent regional epidemics which cause about 3-5 million cases of severe illness and about 290,000 to 650,000 respiratory deaths worldwide.
In recent year’s influenza A subtypes H1N1, H3N2 and influenza B viruses are the prevailing seasonal influenza viruses among human beings. Therefore, type A and B influenza viruses are the only viruses included in seasonal influenza vaccines. Pandemic influenza occurs when new influenza virus appears in a human population that has no pre-existing immunity. Pandemic (H1N1) 2009 was the first pandemic of 21st century.
It was caused by virus of swine origin and was documented as swine flu by media. This pandemic affected 214 countries all over the world. Although, WHO report revealed 18631 laboratory-confirmed deaths during the pandemic, the statistical modelling showed 10 times higher mortality ratecalculated by using H1N1 mortality data retrieved from different countries. Moreover, pandemic virus (H1N1pdm 09) which originated in 2009 continued its circulation as seasonal influenza virus along with subtype H3N2 and type B influenza virus.
Wild aquatic birds such as waterfowl are the principal reservoirs for influenza A viruses. Influenza is not lethal for these aquatic birds as viruses have become adapted in their natural habitat. They can transmit influenza viruses to variety of animals including pigs, horses, sea mammals, birds as well as human beings. Avian influenza viruses which are highly pathogenic are H5, H7 while low pathogenic subtypes are H9 and H10.
By the end of 2005, the highly pathogenic H5NI virus was reported from East, South East, Central Asia and Europe and in February 2006, virus infection was seen in Pakistan, India and Nigeria causing threat to poultry as well as to global community triggering increase chance of next pandemic. Although, animal to human transmission of avian influenza viruses is rare, however, 20 human cases of influenza A (H5N1) were reported in province of Khyber Pakhtunkhwa, Pakistan in 2007.These cases indicate human to human transmission, which is a matter of great public health concern. Influenza A may cause high morbidity with increase hospital expenditures, absteenism from duties and hence, decrease in production capacity of a country, moreover, excessive deaths due to this disease are the major contributing factors for causing burden (both of disease and economy) on a country.
Influenza is believed to be a major cause of mortality and morbidity worldwide but limited number of epidemiologic studies have been conducted in less developed countries like Pakistan. In this regard, we conducted a population-based cross-sectional survey and hospital based sentinel surveillance in 2015-2016.The rationale was to get precise estimates of burden of disease in human population of Lahore, to get better understanding of disease epidemiology in community. We also gathered information on genetic characterization and phylogenetic analysis of circulating virus strains which were collected through hospital based active surveillance.
Our research concluded that pandemic (H1N1pdm09) and seasonal (H3N2) influenza viruses are circulating in local community. A distinct seasonal peak of laboratory confirmed influenza A was recorded in Dec 2015 while cases of respiratory illnesses (other than influenza but influenza-like) were also recorded during study period which were found maximum in February 2016. Moreover, we detected influenza A subtypes, H1N1pdm 09 (28%) and H3N2 (30%) among total influenza A cases (50/311).
Our study confirmed that out of 100 reporting patients to outdoor clinics, 16 are confirmed new cases of influenza A and approximately 10 out of 100 are existing cases (old and new) which were present among population of Lahore. Genetic characterization of viruses indicates that both subtypes H1N1 and H3N2 were found resistant to nearly all anti-viral drugs however, they are sensitive to influenza vaccines recommended by WHO for Northern Hemisphere. So these estimates will enable concerned health authorities to initiate public health interventions at appropriate time to prevent and control next influenza epidemics in a country and include influenza vaccination in national vaccination schedule in order to get effective control over this disease.
—The writer, PhD Epidemiology & Public Health, is based in Lahore.
