Tuesday 16 August 2016

Screwworm screwed

I was a less-than-stellar student in the Genetic Department in TCD in the 1970s. Even as a youth, I had a tendency to flit about from one thing to another and pursue the wrong things with inappropriate energy.  When I should have been knuckling down to studying what was actually on the TCD curriculum, I was off in the library of The Other University [UCD] finding out about inclusive fitness and other material relevant to the then emergent field of Sociobiology. I allowed myself to believe that if I knew quantitative and population genetics really well, I could ignore whole chunks from the rest of the examinable syllabus. I was really interested in Q&PG because it seemed core to understanding evolution but also because it was taught by an outstanding teacher, Paddy Cunningham, who wasn't really on the faculty but had a day-time job in An Foras Talúntais where he eventually finished up as Deputy Director of Research. AFT was established by the Irish Government in 1958 "to review, facilitate, encourage, assist, co-ordinate, promote and undertake agricultural research.". AFT was more or less rebranded as Teagasc in 1988, much to the delight of Irish printers who got large contracts for new letterhead and signage.

Round about the time we came back to Ireland in 1990, Cunningham embarked on a bigger administrative challenge by shipping out to Rome as Director of Animal Production and Health at the Food and Agricultural Organisation (FAO), one of many UN quangos. If no sinecure it was surely a nice billet if you were up to the task: Rome is a cradle of Western civilisation, after all, and the food can be very good. The somewhat ploddy work of FAO's animal health unit was subjected to a very rude awakening almost as soon as Cunningham hung up his hat in his new office.

A consignment of cattle from South America, probably Montevideo, had been shipped to North Africa carrying an infestation of New World screwworm aka blowfly aka Cochliomyia hominivorax [etymology: the snail-shell fly that eats people] The flies were spreading through the African sheep and goat herds from the original focus. Blowfly adults are metallic greeny-blue 2-winged flies about 1cm long. The females mate once and lay 100-400 eggs [cartoon R] in the fur of mammals, especially near wounds, flea-bites or scratches, but also in the nose, vulva or anus if that's the only available opening. Half a day later the eggs hatch into spiney larvae (the screwworms) which plunge into the living flesh and start eating. This feels particularly irritating to the host who scratches at the boil-like larva-filled lesion until it's a bloody mess. The damage looks particularly inviting to other blowflies who lay their eggs nearby: catastrophically extending the wound. About a week after starting to feed the bloated larva drops to the ground, pupates in a quiet spot and hatches out metamorphosed into an adult. The length of the pupal stage is dependent on temperature but it can be as little as 7 days when the cycle starts all over again. The open wounds often overwhelm the animal's innate immune system and get infected with a wide variety of opportunistic bacteria which add the foul smells of necrosis to the already repellent sores.

The people at the FAO were concerned because the New World screwworm is a lot more aggressive, destructive and costly than its Old World counterparts. Two out of two-dozen sheep were fly-struck when we got them sheared, late, this last July. The maggots were icky but it was not a horrible suppurating sore. As you know, they have livestock in America, where C. hominivorax is endemic. But in the 1950s Edward Knipling and Raymond Bushland, working for the USDA, had invented a cunning plan to scupper the lifecycle of the screwworm. It all hinged on the fact the female blowflies mate only once. What if, the two hypothesised, we release enormous numbers of sterile males who will mate with aqll available females who won't then lay viable eggs. Subjecting flies to fairly precise doses of ionising radiation can sterilise the males without inhibiting their desire to mate and ability to fly. This Sterile Insect Technique SIT had been successful in eliminating screwworm from large tracts of prime beef country in North America.

The FAO didn't like the idea of a new disease adding to the hardship of Libyan and Algerian pastoralists, but they were extra twitchy about the possibility that the New World invader would spread to the large livestock in the Serengeti and across sub-Saharan Africa. That would be an ecological disaster of unprecedented magnitude. So they allocated a chunk of money to hit the incipient epidemic really hard while it was still limited in extent. It was similar in concept to the massive investment in Ebola containment which was almost too little too late. The chap tasked to make it happen had just arrived in Rome and he quickly found a telephone booth in which to change.

They decided that SIT had the best chance of success and, rather than starting from scratch locally, FAO contracted with a factory in Mexico to take all the sterile male C. hominivorax that they could produce over the next 12 months. These would be air-freighted weekly from Mexico to Benghazi via Frankfurt. If the timing was right, and this depended on quite precise temperature control throughout the process, the SIT blow-flies could be dumped out of small airplanes as they systematically criss-crossed the affected area. It was a super-elegant precise weapon, that showed how far we have come from spraying DDT from small planes to control other dipteran flies and killing the natural predators of those same flies at the same time <duh!>. It all worked like clock-work, except when one flight was delayed and all the flies hatched out on the runway in Frankfurt. It required much political nicety as well, as it was only a couple of years since the US had bombed Libya and the US was paying for a good part of the SIT program. Over the next months, FAO ground-workers monitored the incidence of fly strike in the region and informed the airplane distribution system so everyone was on the same page. A stark contrast to the 'control' of tuberculosis in Ireland. The North African campaign cost $100 million to release 1.2 billion doctored flies over at area of 40,000 sq.km. And was deemed to be "the most effective and successful international animal health program in the history of the United Nations Organization".

Prof Paddy Cunningham was awarded an honorary doctorate by UCD, his Alma Mater, in 2009, but I don't think the plain people of Ireland really appreciate the giant in their midst.

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