The only constant predictable factorabout influenza is its unpredictability.Whist mankind has advanced

remarkably with antiviral treatments andvaccines; the virus has been outfoxing allattempts to tame it. Smallpox has beeneliminated; polio would have followed thesame fate were it not for politics andmistrust, and some common but potentiallyserious childhood diseases such as measlescan be controlled with well managedvaccination programmes as well as theroping in of the anti-vaccination lobby.

The three viruses mentioned abovediffer significantly from influenza however.Firstly humans are the only objects of theirdesires whilst influenza seeds in severalspecies and can cross specie barriers inunpredictable manners. Secondly they donot change their structure significantlywhilst influenza undergoes geneticrearrangements; subtle drifts over a periodof a few years; or more pronounced, radical,and at times pandemic causing shifts.Thirdly the spread of the three virusesdepends on humans and human behaviour,whilst influenza hitches rides on a variety ofspecies able to cross vast distances.

Influenza has always confoundedscientists. The first recorded pandemic wasin 1578, and enough documentation existsshowing episodic recurrences thereafter.Nothing can compare with The Spanish Fluof 1918 however. This horror episode isestimated to have caused more than 50million deaths, with 10 million being in Indiaalone. Soldiers returning from NorthernFrance at the end of World War One

introduced it to theUSA causing over

600 000 deaths,as well as to

Britain resulting in close to 300 000fatalities. It is one of the great ironies thatsoldiers who did not succumb to the ravagesof the war transported back a much morelethal weapon. It is commonly held that thispandemic was caused by the virus crossingthe species barrier from birds to vulnerablehumans having no resistance to it.

Scientists have since then beenpredicting the next pandemic with variousdegrees of success. The one of 1957originated in China and spread worldwidewithin six months. The 1968 pandemicoriginated in Hong Kong and rapidly spreadvia international air travel and other modesof travel. The last plague epidemic occurredin China. A potentially nightmarish scenarioreared its head with the 2002 Severe AcuteRespiratory Syndrome (SARS) outbreaktaxing scientists and governments alike. It

TRAVELBy Dr Salim Parker President-electSASTM

MEDICINE

spread from mainland China to infectcitizens of 37 different countries withinweeks. It is known that influenza thrives inthe vast avian and porcine reservoirs. Avianinfluenza is well recognised, and justrecently led to the culling of hundreds ofthousands of poultry in Singapore.Indochina has the highest concentration ofhumans with significant interaction with ourfeathered and fattened feasts, so surely thenext pandemic would have to originate inthat region?

Again the virus outwitted us andsimply carried on doing what it wasdesigned to do; replicating, mutating andre-assorting genetic material. A snip of aporcine sequence, a dash of avian input, apinch of human genes and hey presto! Atriple re-assortment was the end productresulting in a potpourri novel to mankind.A mankind with a younger populationcompletely naive to the supposedlyprimitive invader commonly called swineflu, which was later genetically linked tothe 1918 Spanish Flu. And this manifesteditself in Mexico! On 22 April 2009 the firstfew cases were identified in Mexico andthe USA. By the 28th April Mexico reported

The shifting travelcoats of influenza

The wily virus changes its surface glycoproteinsfrequently; drawing by Saaid Rahbeeni

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1600 suspected cases with at least sevendeaths. The spread of swine flu could beclearly linked to air travel out of MexicoCity. Countries such as the USA, Britain,Canada, Spain and Germany were the firstto report cases of the new influenza strainbefore the end of April, reflecting thedensities of air travel between them andMexico. By the 30th April the World HealthOrganisation sent out a warning of animminent pandemic.

On the 1st May European countries, theUSA and Britain reported cases of secondarytransmission, where the disease was spreadlocally. By the 3rd of May, at least 18countries had confirmed cases of thedisease. By the 13th May, only the Africancontinent did not report cases of thedisease, reflecting the paucity of travelbetween it and Mexico. By the 10th June141 countries, including Egypt as the firstAfrican country, had confirmed cases andthe next day the WHO officially declared thepresence of the pandemic. By the end ofJuly 2009 there were over 170 000confirmed cases with more than 1100deaths. The swine flu in effect ‘crowdedout’ other strains of the influenza virus anddominated the landscape for the followingthree years.

Three types of influenza viruses arefound, namely A, B and C. Influenza Aviruses are further sub typed according tosurface glycoproteins called haemagglutinin(H) and neuraminidase (N). Swine flu is thusknown as H1N1, bird flu currently has twoworrying strains. The one that has beenlurking around for the last decade is H5N1.Though it does not easily cross from birds tomankind, it causes thedemise of 50% ofinfected humans.H7N9 is another strainthat again, though noteasily crossing thespecie barrier, is lethalin close to a third ofhumans who areinfected by it. Theconcern is that a smallmutation in eitherspecies would make itfar more transmissibleto us with potentiallydevastating effects.

A few monthsago, a novel avianinfluenza virus causingdisease in penguinswas discovered. Again

not in Eurasia where the bulk of mankindpopulates the land masses but in fact it wasfound in Antarctica! Termed H11N2, it is notconsidered very infectious to humans as it isunable to cause disease in ferrets, a markerof its potential pathogenicity in humans.What was intriguing in the gene sequencesof this penguin flu virus was that somegenetic sequences were from NorthAmerican influenza virus origin, some fromSouth American origin, and some from a fluvirus that is known to cause disease in dogs,horses and birds.

It is speculated that migratory birdsthat fly from land masses to Antarctica,such as giant petrels and skuas, could beintroducing the viruses into the penguinand other populations there. Geneticreassortment and a sudden ability to easilyinfect humans......how far away is the nextpandemic?

TRAVEL MEDICINE

The spread of Swine flu in 2009 could belinked to air traffic out of Mexico City

Giant Petrels cover vast distances between thesouthern continents and Antartica

Spanish Flu struck down thousands of returningWorld War One soldiers

Influenza crosses speciebarriers in unpredictable ways

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