Screwworm - a new menace for Africa
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CTA. 1990. Screwworm - a new menace for Africa . Spore 28. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/45314
A newly-introduced pest poses a serious Ask for Africa's domestic and wild animals and also to the human population. It is the New World Screwworm fly (NWS ), Cochliomyia hominivorax, or 'devourer of man''. Female screwworm flies lay their eggs in...
A newly-introduced pest poses a serious Ask for Africa's domestic and wild animals and also to the human population. It is the New World Screwworm fly (NWS ), Cochliomyia hominivorax, or 'devourer of man''. Female screwworm flies lay their eggs in wounds such as insect bites, scratches, wounds caused by shearing, castration, de-horning and branding or the umbilicus of newborn animals. The eggs hatch into larvae, or maggots, which eat deeply into the living flesh; in a very short time a skin puncture or abrasion as small as a tick bite or scratch can be transformed into a large and dangerous wound. Unless treated quickly, even full grown cattle can die within days. The NSW is the most destructive pest of livestock in the Americas. Its presence outside the Western Hemisphere was confirmed for the first time in April 1989 in Libya. It is thought to have entered Libya on sheep imported from Latin America. The fly has been known to migrate up to 200 kilometres, although the pest most commonly spreads in the larval form through the transport of infested animals. The pest's range used to extend from Florida to Texas in the United States, through Central America and some Caribbean islands into the temperate zones of South America. It has already cost the US and Mexico US$500 million to eradicate the screwworm from the US and most of Mexico. It is feared that if the pest is not eradicated very quickly from Libya, it will spread into neighbouring countries, across the Sahara into tropical Africa and even around the Mediterranean basin, into Southern Europe, and possibly into West Asia. Eradication the aim It is possible to treat domestic livestock attacked by NWS but great expense and effort are involved. The possible effects on the wild animal population of Africa which cannot be treated, are alarming. Once infested, wild animals would become a continuing reservoir of infection probably causing more widespread and devastating losses than tsetse. The female screwworm lays clutches of up to 400 eggs at about three-day intervals before she dies. Larvae hatch 11 to 24 hours later and begin to feed on the host's tissues. The wounds produce an odour that then attracts more flies. After feeding and growing for four to eight days, the larvae drop to the ground, burrow into the soil and pupate. Adult flies emerge in as little as seven days and complete a life cycle that can be as short as three weeks (see diagram). The only worthwhile option is to eradicate the screwworm totally and the only proven technique is to combine the release of sterile male flies from the air with strict ground controls on the movements of animals, quarantine, monitoring and preventative treatment of wounds. The sterile insect technique (SIT) was pioneered in the US 33 years ago. A special rearing centre propagates flies and bombards the larvae with a carefully controlled dose of gamma radiation to make them sterile without weakening or reducing the male's desire to mate. The irradiated pupae are packaged and delivered to the infested area, ready to hatch. The flies are then loaded into light aircraft for dispersal. The technique is effective because the female NWS, mating with a sterile male, lays eggs that do not hatch. The female usually mates only once while the males mate five or six times; saturating an area with sterile males, that greatly outnumber the local fertile males, and results in population decline and eventual eradication. Action to-date The Libyan Government has already spent over $7.5 million to fight the screwworm. It has fielded more than 90 teams to inspect and treat wounded animals every 21 days in the infested and adjacent areas and has set up 12 quarantine stations to control movement of animals. In July 1989, FAO and the UN Development Programme organized a regional training course for officials from Libya, Algeria, Chad, Egypt, Niger, Sudan, Morocco and Tunisia. A second training course was held in Libya in March for African countries farther from Libya, which are considered 'the second line of defence.' And components for 1,750,000 animal treatment and sampling kits together with information material in Arabic, English and French have been provided to Libya and neighbouring countries. To meet the North African emergency, transport planes will make at least two deliveries each week of irradiated flies from Mexico to the operation headquarters in Libya. Millions of flies will be released to achieve a ratio of at least 10 sterile males to each local male. FAO estimates that it would cost $42 million per year for two years to mount a full eradication programme. However, this expense is only a fraction of the losses that a widespread infestation would cause. If it is not eradicated from Libya, the estimated costs of controlling the screwworm in the five countries of North Africa alone would exceed $250 million per year. The costs of further spread are incalculable: this is truly a now-or-never opportunity to eradicate screwworm from Africa. For further information contact: The Information Division Food and Agriculture Organization of the united Nations Via delle Terme di Caracalla 00100 Rome - ITALY