A longitudinal study of Plasmodium falciparum malaria in the West African savannah using the ELISA technique.

Malarial antibody levels were measured by the enzyme-linked immunosorbent assay (ELISA) in two West African populations, one exposed to intense malaria transmission and the other protected. The results reflected the transmission of maternal antibody and, in the unprotected population, the subsequent increase of the ELISA values with age reflected the development of the immune response to malaria. Malaria control activities reduced ELISA values in the protected population. The limitations of the ELISA test used in this study are shown by the fact that numerous infants with previous proven parasitaemia were ELISA-negative. Purified antigens are needed to improve the ELISA test for use in serological surveys of malaria.

Abnormal haemoglobins in the Sudan savanna of Nigeria. III. Malaria, immunoglobulins and antimalarial antibodies in sickle cell disease.

Subjects with sickle cell disease were identified in (i) a whole population sample (2742) Garki District, Kano State, Nigeria, and in (ii) the 534 infants born into the population during five years. Eleven (2.1%) newborn had Hb.SS, as was expected from gene frequency (0.146). Prevalence was maintained in the first year of life, but fell to 0.4% at one to four years and to 0.05% (one person) over the age of nine years. Antimalarial intervention for two transmission seasons was followed by an apparent but not significant decrease in Hb.SS mortality. There was one male aged about 40 years who had Hb.SC (the expected number was three). Hb.SS children were compared to normal subjects at the same age, the same village and the same survey; they had significantly less than the expected Plasmodium malariae infection (P less than 0.01) and lower than median P. falciparum densities while below five years (P less than 0.05). Over one year of age, they tended to have below average indirect fluorescent antibody (IFA) (P less than 0.01), indirect haemagglutinating antibody (IHA) (P less than 0.01) titres and number of precipitin rings (not significant) against P. falciparum antigen, and IFA against P malariae (P less than 0.01). They had above average IgM (P less than 0.05), but their IgG concentrations did not differ from normal. We conclude that (i) sickling is sufficient to protect against P. malariae in Hb.SS but not Hb.AS; (ii) sickling prevents intense P. falciparum infection in Hb.SS, as in Hb.AS; (iii) in Hb.SS, there is less antigenic stimulus and hence less antibody against P. falciparum (like Hb.AS) and P. malariae (unlike Hb.AS); (iv) although less intense, malaria is frequently fatal in Hb.SS, especially in age-group one to four years (unlike Hb.AS); (v) IgM levels are high in Hb.SS in response to frequent infections other than malaria (unlike Hb.AS).

Abnormal haemoglobins in the Sudan savanna of Nigeria. IV. Malaria, immunoglobulins and antimalarial antibodies in haemoglobin AC individuals.

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).

Abnormal haemoglobins in the Sudan savanna of Nigeria. II. Immunological response to malaria in normals and subjects with sickle cell trait.

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.

Longitudinal serological study of malaria in infants in the West African savanna. Comparisons in infants exposed to, or protected from, transmission from birth.

Two infant populations, the one exposed to intense malaria transmission and the other protected, were followed and compared by six serological tests. The IgG and IgM levels increased with age and were systematically, though only slightly, lower in the protected children. The results of three Plasmodium falciparum tests (precipitin, indirect fluorescent antibody (IFA) and indirect haemagglutination and one P. malariae test (IFA) were high at birth and decreased rapidly afterwards in both populations. In the unprotected population, this decrease was followed by an increase, closely associated with the parasitological findings, while in the protected population the decrease continued to very low levels.

Changing patterns in the humoral immune response to malaria before, during, and after the application of control measures: a longitudinal study in the West African savanna.

A longitudinal seroimmunological investigation of malaria was performed as part of the WHO research project conducted in the northern part of Nigeria from 1970 to 1975. The project included a preintervention phase, an intervention phase with application of malaria control measures (spraying of residual insecticide and mass drug administration), and a postintervention phase. Serological observations were made on the total population of eight villages consisting of approximately 3000 persons. Six immunological parameters were studied, namely, the serum levels of IgG and IgM, the number of bands of precipitation for Plasmodium falciparum in the double diffusion (Ouchterlony) test, the titres of antibodies for P. falciparum and P. malariae in the indirect fluorescent antibody (IFA) test, and the titres of agglutinating antibodies for P. falciparum by the indirect (passive) haemagglutination (IHA) test. The serological results were used to evaluate the impact on the humoral immune response of different levels of parasitaemia resulting, in the unprotected population, from natural factors such as seasons and ageing and in the protected population, from human intervention through the application of control measures and their interruption. The linkage by computer processing of the longitudinal data allowed analysis of the relationship between the results of a serological test in the same person at different surveys, and analysis of correlation between serological results and the concurrent parasitological findings. The correlation between parasitaemia and the results of the different serological tests at the same survey in the same person were also examined and analysed in terms of sensitivity and specificity of the tests.