1. Wolfson Tropical Pathology Unit and Medical Helminthology, London School of Tropical Medicine and Hygiene, Keppel Street, WC1 E7HT, United Kingdom,
2. Department of Microbiology and Public Health, Michigan State University, East Lansing, Michigan,
3. and
Khartoum Eye Hospital, Khartoum, Sudan
4. St. Vincent's Hospital, Melbourne, Australia,