In response, the USDA released over 80 million sterile flies from 25 ground release sites on twelve islands and the city of Marathon. The first, and to-date largest, documented infestation of "C. hominivorax" myiasis outside of the Americas occurred in North Africa from 1989 to 1991. The outbreak was traced to a herd of sheep in Libya's Tripoli region, which began suffering screwworm attacks in July 1989; over the following months, the myiasis spread rapidly, infecting numerous herds across a 25,000 km2 area. Eventually, the infested region spanned from the Mediterranean coast to the Sahara Desert, threatening the more than 2.7 million animals susceptible to "C. hominvorax" that inhabited the area. More than 14,000 cases of large-scale myiasis due to the "C. hominivorax" species were documented. Traditional control methods using veterinary assessment and treatment of individual animals were insufficient to contain the widely dispersed outbreak, so the United Nations Food and Agriculture Organization launched a program based on the sterile insect technique. About 1.26 billion sterile flies were produced in Mexico, shipped to the infested area, and released to mate with their wild counterparts. Within months, the "C. hominvorax" population collapsed; by April 1991, the program had succeeded in eradicating "C. hominivorax" in the Eastern Hemisphere. This effort, which cost under US$100 million, was among the most efficient and successful international animal health programs in UN history. The North African outbreak both provided proof of the sterile male technique's efficacy and led to numerous enhancements in its implementation; after 1991, it entered into use across parts of Central and South America. However, the inaccessibility of some areas that the fly inhabits, language differences, and the need of constant vigilance have slowed the eradication of this species. Research is currently being performed to develop a synthetic odor bait to replace the use of wounded animals as bait for the females of "C. hominivorax". This previously used method has fallen out of favor. The synthetic bait is formulated to mimic natural wound fluid from animals. The female flies are attracted to animal wounds to obtain a protein meal and to oviposit. The synthetic bait could be used at research stations that monitor for flies in regions where they are eradicated and to help decrease the screwworm populations in infested regions. The secondary screwworm, "C. macellaria", is a flesh-eating fly whose larvae consume only necrotic tissue, either that of carrion or of an animal or human host (myiasis).