[1] UNIV KHARTOUM, FAC VET SCI, DEPT VET PATHOL, KHARTOUM, SUDAN
[2] UNIV GLASGOW, FAC VET MED, DEPT VET PHYSIOL, GLASGOW G12 8QQ, SCOTLAND
[3] UNIV LONDON LONDON SCH HYG & TROP MED, TROP EPIDEMIOL UNIT, LONDON WC1E 7HT, ENGLAND
[4] UNIV LONDON LONDON SCH HYG & TROP MED, DEPT MED HELMINTHOL, LONDON WC1E 7HT, ENGLAND