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The detection of haptoglobins in Anopheles gambiae s.l. has been used to obtain an estimate of the incidence of multiple feeding for the village of Barmawa, Garki District, Kano State, Nigeria. The results indicated that the incidence of multiple feeding was approximately 10% but problems were encountered by the high incidence of ahaptoglobinaemia in the population. In four villages in Garki District the incidence of ahaptoglobinaemia varied between 65 and 76% while in young children and personnel under constant malaria chemoprophylaxis it was less than 30%. A strong correlation between ahaptoglobinaemia and malaria infections was seen. The results show evidence of selection of hosts by mosquitoes at Barmawa although this does not necessarily imply a preference per se. The results provide evidence of movement of blood-fed mosquitoes, between houses and from houses to resting sites.

Children born in areas hyperendemic for Plasmodium falciparum are protected by maternal antibodies for up to about five months of life, after which they are subject to intense infection until they acquire sufficient immunity--by about five years of age. Children with sickle cell trait (Hb.AS) are at an advantage during these critical years, probably because of preferential phagocytosis of parasitized red cells. This could lead to either (i) early processing of antigen by macrophages and an accelerated immune response, or (ii) less antigenic stimulus and hence lower antibody production. Immunoglobulin (Ig)G and IgM determinations, agar gel diffusion (Ouchterlony) against soluble P. falciparum antigen, the indirect fluorescent antibody (IFA) test using P. falciparum and P. malariae antigens, and the indirect haemagglutination (IHA) test with P. falciparum antigen were performed on sera from a population with different Hb electrophoretic types in the hyperendemic malarial area of Garki, Kano State, Nigeria. Plasma immunoglobulins and antimalarial antibodies rose with age. After the first year of life, lower mean concentrations of immunoglobulins (especially IgM), and lower mean titres of antibodies specific against P. falciparum (Ouchterlony, IHA and less significantly IFA) were present in Hb.AS compared to Hb.AA; these differences increased with age. Antimalarial intervention was followed by a decline of all values and final levels showed little difference between haemoglobin types. It was unlikely that either a relative inability to produce antibody or a more rapid catabolism of immunoglobulins was responsible for the lower levels in sickle cell trait. The observations are more easily explained by the hypothesis that Hb.AS persons have less antigenic stimulus due to the early removal of parasitized sickled cells by macrophages, which then degrade the antigens. The antibody difference between Hb.AA and Hb.AS increased throughout life, suggesting that this process remained a feature of sickle cell trait even after parasite frequencies and densities were similar in the two Hb groups. These observations have implications in the aetiology of tropical splenomegaly syndrome, which is rarely seen in sickle cell trait subjects. Mean IgG and IgM were slightly higher in Hb.AS than Hb.AA infants, the difference for IgG achieving significance. This suggested that during infancy early phagocytosis of parasitized cells had led to enhanced processing of antigen and hence an earlier immune response in Hb.AS, but this was unlikely to be a major factor in survival. IFA titres against P. malariae were slightly but not significantly lower in Hb.AS, possibly as a result of cross-reaction with P. falciparum antibody or of a slight degree of protection against P. malariae.

Haemoglobin (Hb) AC electrophoretic pattern was found in 0.7% of the population at Garki, Kano State, northern Nigeria, an area where malaria is hyperendemic. Twenty-one Hb.AC subjects at all ages did not differ from the rest of the population in their frequency or density of Plasmodium falciparum, P. malaria or P. ovale infections, nor in their IgM concentrations and titres of specific antimalarial antibodies. However, IgG levels in Hb.AC subjects were frequently above the average of the reference population (P less than 0.05), especially during a period of protection against malaria (P less than 0.01). These observations suggest that the Hb.C gene may be maintained in certain environments by an enhanced ability to produce IgG antibodies against an antigen or antigens other than malaria, and that its geographical relationship to malaria may be a coincidence. This hypothesis needs to be tested where Hb.C is seen at high frequency, in northern Ghana and Upper Volta or Gwoza (Nigeria).

A comparative trial was carried out in northern Nigeria of the ability of the drug combinations chloroquine-pyrimethamine and sulfalene-pyrimethamine to clear the peripheral blood stream of asexual forms of P. falciparum within 7 days. The reappearance of asexual P. falciparum forms within the 70-day follow-up period and the occurrence of vomiting during the 2-3 hours following administration of the drugs were also recorded. The purpose of the trial was to choose the more suitable of the two drug combinations for repeated mass administration in the intervention phase of a collaborative field research project in the epidemiology and control of malaria in the African savannah. No differences were observed between the two drug combinations from a parasitological point of view. However, the sulfalene-pyrimethamine combination was found easier to administer and occasioned fewer records of vomiting. It was therefore recommended for use in the project.