Susceptibility Test Methods: Parasites

Drug susceptibility tests fall into four broad categories: in vivo tests, in vitro tests, tests with experimental animals, and molecular tests. These different categories of tests provide complementary information. At one end of the spectrum, molecular tests analyze parasites at their most basic biologic level, without any outside interference. Most drug resistance tests in malaria concern Plasmodium falciparum, the most prevalent and virulent species and the most prone to the development of resistance. Incorporating pharmacokinetic parameters is now considered essential for true resistance identification within partners of artemisinins, which are frequently poorly absorbed or slowly eliminated drugs. While treatment failures for Trichomonas vaginalis infections have often been disregarded as being due to poor patient compliance or rapid reinfection, there is an increasing recognition that true clinical resistance exists and may be increasing, thus necessitating accurate drug susceptibility testing of patient isolates. Treatment failure in leishmaniasis may result from either true drug resistance or patient immunodeficiencies that preclude effective chemotherapeutic action. Differentiation of these two possibilities is important for both individual patient care and general public health. A standardized in vivo method for detection of drug resistance that was designed for testing trypanosomes that infect cattle can also be applied to those that infect humans. Investigation of drug resistance mechanisms of schistosomes is more difficult and time-consuming than those associated with protozoan infections.