New opportunities for the diagnosis and control of animal diseases in the tropics

Effect of strategic gastrointestinal nematode control on growth of N'Dama cattle in Gambia

From October 1989 to December 1994, a longitudinal study on the control of gastrointestinal nematodes was done on 1000 N'Dama cattle in 20 private herds in Gambia. Each herd was divided into two groups with an even distribution of age and sex. One group received a single anthelmintic treatment of Fenbendazole, Panacur Hoechst Veterinär GmbH, 7.5 mg kg-1 BW in October 1989, whereas the other group served as an untreated control. In July 1990, the herds were subdivided into two different treatment schemes. In the herds of the first scheme the treated animals (Treatment group I) were treated once (in August), whereas in the herds of the second scheme the treated animals (Treatment group II) were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. One group in every herd served as control (Treatment group 0) and received no anthelmintic treatment throughout the study. One annual fenbendazole treatment had no significant effect on liveweights, whereas two annual treatments significantly increased liveweights of the age group 12-24 and 24-36 months by 9.4%, and 17.5%, respectively. Animals less than 12 months old had 6.3% higher liveweights after two treatments, the difference was statistically not significant (P < 0.06). Average weights of 3- and 4-year-old, twice-treated animals were 13.1% and 8.2%, respectively, higher compared with their controls. No effect of anthelminthic treatment on liveweights was found in 5-year-old and older animals. Herd structure analysis demonstrated that overall male offtake rates ranged from 12 to 28% in the 3-, 4- and 5-year-old age categories. The age categories within which deworming improves liveweights thus coincides with the age at which males are mainly sold. These results suggest that biannual metaphylactic treatments (end of July and beginning of September) of all animals from birth to an age of 4 years should be recommended, provided that the financial analysis demonstrates the profitability of this intervention.

Resistance to diminazine aceturate by Trypanosoma congolense from cattle in the Zambezi Valley of Zimbabwe

The susceptibility of 14 stocks of Trypanosoma congolense, recently isolated from cattle, to therapeutic doses of diminazene aceturate and to isometamidium chloride was assessed in laboratory mice. Eight isolates were readily susceptible to the normal therapeutic dose of diminazene, two were resistant to the drug at 14 mg kg-1, and four were totally resistant at 28 mg kg-1. All the isolates were susceptible to isometamidium chloride at 0.5 mg kg-1. These observations highlight the need for regular evaluation of drugs used in the control of trypanosomosis.