Biochemical and metabolic peculiarities of some parasites availing as targets for therapy.

Biochemical and metabolic peculiarities of some parasites involved in their interactions with their hosts are reviewed according to (1) carbohydrate metabolism comprising glycolysis, Pasteur effect, CO2 fixation and electron transport system; (2) amino acid and protein metabolism ; (3) purine and pyrimidine nucleotides metabolism. These peculiarities are becoming targets for treatment without affecting the host.

The mechanisms of action of antiprotozoal and anthelmintic drugs in man.

The mechanisms of action of antiprotozoal and anthelmintic drugs are reviewed according to: (1) drugs interfering with metabolic processes; (2) drugs interfering with reproduction and larval physiology; and (3) drugs interfering with neuromuscular physiology of parasites.

Two potential improvements to BCG and their effect on skin test reactivity in the Lebanon.

An account of an ongoing project to assess the possible benefits of two additives to BCG vaccine is presented. These additives are suspensions of irradiation killed Mycobacterium vaccae in one case, and M. leprae in the other. Groups of children aged 7-17 living in Zgharta and Akkar districts of North Lebanon have received vaccination with BCG alone or with either of the two additives since 1980. This region was chosen since contact with environmental mycobacteria is small, but both leprosy and tuberculosis occur there. So far the effects of the additives have been assessed by annual skin testing of volunteers with Tuberculin, Leprosin A, Vaccin and Scrofulin, and by measuring the size of the vaccine scars. Some children have now been followed up on four occasions, and special attention is paid to them. No complications have been encountered in the 1740 children who have entered the study (by our observation, or by local report on those who have not attended for follow-up) and the mean scar sizes after vaccines with the additives are no larger than those after BCG alone. There is no evidence that the additives have prevented development of Tuberculin positivity after vaccination, or have changed the nature of reaction to it. Incorporation of M. leprae significantly increased Leprosin A positivity and both additives increased Vaccin positivity in comparison with the effects of BCG alone. The results are fitted to a model of the theoretical expectations of the study and may be beginning to show the advantages expected of the additives. The only unexpected finding was a reduction in Scrofulin positivity especially associated with the additives. The very low contact with environmental mycobacteria experienced in the study area has allowed the pattern of post-vaccination decay of skin test positivity to be studied with greater precision than has been reported before, and differences have been detected between the two districts where the study was conducted. Confirmation of the possible advantage of the additives will rest with data to be obtained in longer term follow-ups and in studies being carried out in other countries.

Skin sensitization to mycobacteria amongst school children prior to a study of BCG vaccination in North Lebanon.

1888 school children aged between 7 and 17 years, living in 13 villages in two districts of North Lebanon, were skin tested with four new tuberculins as the initial step in a study of BCG vaccination. The great majority of children were tested with Tuberculin, Leprosin A, Vaccin and Scrofulin. In comparison with other countries where similar studies have been carried out, extremely low levels of sensitization were discovered, indicating very little contact with mycobacteria. There was, however, a statistically significant increase in positivity with increasing age. The results obtained for the villages of each district were significantly different from each other, positivity being greatest in Akkar district for each reagent. The eight villages of Zgharta district could be separated into a lowland group of four villages, a mountain group of three villages and one anomalous mountain village. There was significantly more positivity in the lowland than in the mountain villages. In Akkar district, where leprosy has a low prevalence, positivity to Leprosin A was 8% amongst the children (leaving out an anomalous village). In Zgharta district where the disease does not occur, positivity was 3.4% to Leprosin A for the lowland villages and 0.9% for the group of 3 mountain villages. The two anomalous villages were the only ones in which tuberculosis cases were known to have occurred recently, and they were the only two villages in which Tuberculin positivity exceeded 10%.

Treatment of hydatid cysts (Echinococcus granulosus) by Cetrimide (R).

Cetrimide (R) has been efficiently assessed against hydatid protoscolices as a scolicidal adjunct to hydatid surgery. It was tested in four concentrations (0.05, 0.1, 0.5 and 1%) against the protoscolices of hydatid cysts in sheep and cattle and in 0.1% concentration against the protoscolices of hydatid cysts in humans. For each concentration, three incubations of one, five and 10 min exposure were tested in vitro and in vivo on sheep and cattle cysts, and two successive incubations each of five min exposure on human cysts. All experiments resulted in rapid mortality of the protoscolices, as judged by their loss of motility, readiness to take vital stains and inability to develop into secondary hydatid cysts when inoculated into albino mice. The low toxicity of Cetrimide (R), its rapid action against the protoscolices, its scolicidal effect at a low concentration, and its low degree of absorption by the host tissues make it the most promising drug in hydatid surgery, displaying no side effects on the host.

The host response in secondary hydatidosis of mice. I. Circulating antibodies.

The infection of young albino mice by the intraperitoneal injection of viable hydatid protoscolices provided a suitable model for the investigation of the factors controlling the subsequent host immune response. Antibodies detectable by haemagglutination and complement fixation appeared around the 14th week after infection. Increases in antibody titres were related to the potency of the antigenic impulse(s) produced by the healthy germinal membrane and viable protoscolices. Our results suggest that qualitative and quantitative variations in excretory, secretory and somatic antigens, occurring during the different phases of parasite development, incite the production of a multitude of antibodies, only a few of which are detectable by conventional methods.