Pharmacology of diminazene. A review

Publisher Summary Recent biological investigations of the African trypanosomes have been moving away from their previous preoccupation with the phenomenon of antigenic variation. The feeling has arisen that antigenic variation, as demonstrated by the Trypanozoon and Nannomonas subgenera of trypanosomes, is too extensive, the number of serodemes too large, and the coexistence of different species in many areas too complicated, to allow any immunoprophylaxis based on antibodies to variable antigens. However, in the case of T. vivax, more information is required concerning antigenic variation and coat structure in this organism before these avenues of investigation are discarded. The ways of improving the yield of mature metacyclic trypanosomes in vitro must be found, so that the contribution of metacyclic variable antigens to the induction of immunity in T. vivax infection can be elucidated. The number of bloodstream variable antigen types (VATs) must be determined, as there is evidence both for VAT exhaustion contributing to the self-cure of infected hosts and for a possible limit to the number of VATs that can be expressed in infections in Africa. It is probable that new DNA probes will have to be prepared to ensure the identification of all the members of this geographically dispersed species of protozoan parasite.

Recent Studies of the Biology of Trypanosoma vivax

Present status of chemotherapy and chemoprophylaxis of animal trypanosomiasis in the Eastern hemisphere.

Chemotherapy and delivery systems: haemoparasites

Publisher Summary This chapter discusses the interaction between trypanosomatid flagellates and their invertebrate hosts—the majority of those discussed are vectors. It also discusses the lower vertebrate trypanosomes and their vectors and mammalian trypanosomes and their vectors. Trypanosoma (Herpetosorna) rangeli (T. Rangeli) is one of the most interesting of mammalian trypanosomes. It is a parasite of man and various mammals in Central and South America and is transmitted by the bite of reduviids, usually Rhodnius prolixus. T. (H.) rangeli is pathogenic to its vector. The relationship between mammalian and reptilian Leishmania may prove to be of importance in understanding the epidemiology of the human disease. The chapter elaborates on the monoxenous trypanosomatid in insects. Under natural conditions, there are several situations in which an individual vector may be infected with more than one species of trypanosomatid. Thus, the effects of one parasite on another may be important in the context of competition for sites of establishment and available vector resources or because one species may be pathogenic to the vector, thus reducing the transmissibility of both parasites. Mixed infections between trypanosomes and monoxenous flagellates will occur in many situations, but few have been discussed in the chapter.

Vector relationships in the Trypanosomatidae.

Two strains of T. congolense and two strains of T. vivax, resistant to normal therapeutic doses of trypanocidal drugs, were transmitted by G. morsitans and G. tachinoides through series of cattle in the absence of drugs to assess the transmissibility of the trypanosomes by tsetse flies and the stability of drug resistance in the organisms during cyclical development. The characteristics of both strains of T. vivax and one strain of T. congolense were typical of the species, but the infectivity of the second strain of T. congolense for laboratory animals was abnormally low. The transmissibility of the trypanosomes was assessed on the bases of the infection rates in tsetse flies used to transmit the strains and the periods required for the development of the trypanosomes in the flies and bovine hosts. The transmissibilities of both strains of T. vivax and the first strain of T. congolense were normal by comparison with data obtained by cyclically transmitting non-resistant trypanosomes of the same species, but the period required for the development of the second strain of T. congolense in tsetse flies was abnormally long. There was no loss of drug resistance in any of the strains examined in the experiments. A strain of T. congolense retained resistance to diminazene aceturate at a dose rate of 7-0 mg/kg, homidium chloride at 2-0 mg/kg, quinapyramine sulphate at 4-4 mg/kg and isometamidium chloride at 0-5 mg/kg during a series of eight transmissions by tsetse flies in a period of 376 days.

A. R. Gray

Papers

The cyclical transmission of strains of Trypanosoma congolense and T. vivax resistant to normal therapeutic doses of trypanocidal drugs.