Conventional parasite control measures
are based on the use of curative (chemotherapy) and preventive
Only three drugs are available - isometamidium chloride,
diminazene aceturate and homidium (bromide and chloride).
These compounds have been on the market for over 40 years.
It is currently estimated that 35 million doses of these chemicals
are used in Africa each year and that between 40 million and
60 million cattle are at risk. Although there is a consistent
demand for trypanocides by African farmers and national veterinary/livestock
services, the total value of the market (more than US$ 30
million) is not considered sufficiently financially important
to justify investment by large pharmaceutical companies in
the development and licensing of new trypanocides, the cost
of which may exceed US$250 million for a single compound.
Perhaps the greatest risk to the future use of existing trypanocides
is the development and spread of drug resistance in parasite
populations to the point they become ineffective over large
areas of Africa. Resistance to one or more of the trypanocidal
drugs used in cattle has been reported in at least 13 countries
of sub-Saharan Africa. Very few systematic surveys have been
carried out and the occurrence of drug resistance was found
to be greater in those regions where drug use was more intensive
which led to the selection of resistant strains.