Malaria in an urban and a rural area of Zambia.

Children in Lusaka and in a rural area in central Zambia were examined during November 1984 and April 1985 to assess the effect of urbanization on malaria transmission. Of 423 urban children examined in November, 2.4% had scanty parasitaemia, and low titres of malarial antibodies were found in 46%. These proportions increased in April to a parasite rate of 10.3% and malaria antibodies were detected by indirect fluorescent antibody tests (IFAT) in 62%. The presence of malaria antibodies was positively associated with journeys outside the main towns. Examination of paired sera from the 2 periods showed an association between a history of malaria and an increased antibody titre, but failed to show an association between travel outside the main towns and conversion from a negative to a positive IFAT. The spleen rate in children under 15 years old in Lusaka was 3%, indicating hypoendemic malaria. In rural children the parasite rate was 10% and 27% in the 2 seasons, respectively, and over 97% of the children had malaria antibodies. The spleen rate was 20%, indicating mesoendemic malaria. It is concluded that there is only low transmission of malaria in Lusaka so that many people do not develop resistance and are therefore at risk of severe attacks if they do become infected. Possible measures to protect the urban population are discussed.

Effect of a malaria suppression program on the incidence of African Burkitt's lymphoma.

From 1977 to 1982, the authors attempted a malaria suppression trial in North Mara District, Tanzania, to see whether the incidence of Burkitt's lymphoma (BL) could be lowered by reducing the level of malarial infection in a child population below 10 years of age. Immediately after initiation of the suppression trial, the prevalence of malaria fell drastically in the Mara children; however, soon after, the rate of malarial infection rose again in the trial area in spite of continued chloroquine distribution, and by 1981 the prevalence of malarial infection again reached the high levels that had prevailed in the North Mara lowlands before 1977. However, during the period of chloroquine distribution in North Mara, the level of malarial infection there was constantly lower than that observed in a comparison area in South Mara, although the two areas had been similar with respect to malaria endemicity prior to the intervention. During the years of chloroquine distribution in North Mara, the incidence rate of BL there fell considerably, from about 4 per 100,000 population to about 1 per 100,000 population, and it rose again to pretrial levels in 1984, that is, about two years after the chloroquine distribution had been terminated. This apparent association between malaria suppression and decline in BL incidence at first seemed to indicate that malaria is a causal factor in BL production. A close scrutiny of the survey data revealed, however, that the decline in BL incidence might have started several years before the chloroquine distribution began; thus it appears that the malaria suppression could not have been the sole cause of the BL decline.

Serial studies on the evolution of drug resistance in malaria in an area of east Africa: findings from 1979 up to 1986.

Observations, previously reported for 1979-82, have been continued up to 1986 on the development of drug resistance in P. falciparum in the North Mara area of Tanzania, where a chloroquine chemosuppression campaign was attempted from 1977 to 1982. The WHO micro in-vitro test for chloroquine and other drugs was used. Because of the large number of tests done, each test was characterized by the mean minimum inhibitory concentrations (MIC) of drug needed to prevent schizont development instead of counting the numbers of schizonts. The MIC for chloroquine has risen progressively each year but changes in the findings of in-vivo tests were less dramatic possibly due to the effects of immunity. Resistance to amodiaquine has followed that to chloroquine at a lower level, and in the last years the MIC for quinine has risen. Sporadic resistance to mefloquine was found and, by in-vivo test, to sulphadoxine-pyrimethamine. Possible factors in the evolution of drug resistance are discussed together with implications for the future.

Seroepidemiological studies of leprosy in northern Malawi based on an enzyme-linked immunosorbent assay using synthetic glycoconjugate antigen.

A total of 6002 blood samples from total population samples in four separate areas within Karonga District, Northern Malawi, were tested for anti-Mycobacterium leprae antibody using an ELISA based on synthetic glycoconjugate antigen. Results are presented using different criteria for seropositivity. Regardless of the criterion used, the proportion of individuals classified as "positive" rose to a peak at 20-30 years of age and then fell, and it was higher at all ages in females than in males. There was no difference in seropositivity levels between individuals with or without BCG scars. Although leprosy cases, in particular those with positive smears, had higher antibody levels than nonleprosy cases, analysis of age-standardized data revealed only weak evidence for a correlation between the prevalence rates of clinical leprosy and of seropositivity within the four areas. There was no evidence for higher seropositivity levels in household contacts of leprosy cases compared to noncontacts. The implications of these results for the epidemiology of leprosy in this population are discussed.

Seroepidemiological studies of leprosy in northern Malawi based on an enzyme-linked immunosorbent assay using synthetic glycoconjugate antigen

"A total of 6002 blood samples from total population samples in four separate areas within Karonga District; Northern Malawi; were tested for anti-Mycobacterium leprae antibody using an ELISA based on synthetic glycoconjugate antigen. Results are presented using different criteria for seropositivity. Regardless of the criterion used; the proportion of individuals classified as ""positive"" rose to a peak at 20-30 years of age and then fell; and it was higher at all ages in females than in males. There was no difference in seropositivity levels between individuals with or without BCG scars. Although leprosy cases; in particular those with positive smears; had higher antibody levels than nonleprosy cases; analysis of age- standardized data revealed only weak evidence for a correlation between the prevalence rates of clinical leprosy and of seropositivity within the four areas. There was no evidence for higher seropositivity levels in household contacts of leprosy cases compared to noncontacts. The implications of these results for the epidemiology of leprosy in this population are discussed."

Ahaptoglobinaemia in Melanesia: DNA and malarial antibody studies.

To assess the relative contributions of genetic and acquired factors, particularly malaria, to the high frequencies of ahaptoglobinaemia found in Melanesia we have performed DNA and malarial antibody studies in a population from Vanuatu. No gene deletion or rearrangement was found on gene mapping in any ahaptoglobinaemic individual and the frequencies of the Hp1 and Hp2 alleles in the ahaptoglobinaemic group were similar to controls. However, antibodies to Plasmodium falciparum were significantly elevated in the ahaptoglobinaemics. These data suggest that malaria rather than genetic factors is the major cause of ahaptoglobinaemia in Melanesia.

Serial studies on the evolution of chloroquine resistance in an area of East Africa receiving intermittent malaria chemosuppression.

Serial in vitro and in vivo tests for chloroquine sensitivity of Plasmodium falciparum were carried out from 1979 to 1982 in an area of E. Africa where chemosuppression with chloroquine had been attempted since 1977. Within 1(1/2) years there were signs of a decreasing drug response. Chloroquine resistance was first detected in 1981 and this increased markedly in 1982. Other contributory causes for the rise of parasite rates in children were possibly a decline in the efficiency of the drug distribution system and also immunological factors. Evidence of resistance to pyrimethamine was also found. Observations were made of the heterogeneity of the parasites' responses with emerging resistance. Implications for the future are discussed.

Observations on early and late post-sporozoite tissue stages in primate malaria. III. Further attempts to find early forms and to correlate hypnozoites with growing exo-erythrocytic schizonts and parasitaemic relapses in Plasmodium cynomolgi bastianellii infections.

Rhesus monkeys were heavily infected with sporozoites of Plasmodium cynomolgi bastianellii in an attempt to demonstrate the site of invasion of sporozoites into tissue cells and their growth there. Further attempts were made to correlate the appearance and loss of hypnozoites with parasitaemic relapses. Hypnozoites were demonstrated and once again shown to decrease in numbers over 229 days during which time the infection showed parasitaemic relapses. Liver biopsies taken at two-day intervals for 12 days showed that hypnozoites decreased in numbers over-all and growing schizonts were demonstrated in the liver. At this time a parasite the size of a hypnozoite was seen with two nuclei and another was seen with an elongate, possibly dividing nucleus in one monkey. an attempt to find the location of the early intracellular exoerythrocytic forms in the liver at various times less than 40 hours after infection using smears and immunological staining with newly prepared anti-sera failed. Large numbers of sporozoites of P. knowlesi were also injected into a rhesus monkey the liver of which on the fifth day after infection showed no hypnozoites among 157 sections of growing schizonts and no parasites at all on the 42nd day after infection. In P. cynomolgi bastianellii infections parasites, mostly hypnozoites, were found in the liver up to 229 days after infection.

Observations on early and late post-sporozoite tissue stages in primate malaria. II. The hypnozoite of Plasmodium cynomolgi bastianellii from 3 to 105 days after infection, and detection of 36- to 40-hour pre-erythrocytic forms.

Confirmation of the existence of a persistent, uninucleate, dormant pre-erythrocytic stage, the hypnozoite, of the relapsing simian malaria parasite, Plasmodium cynomolgi bastianellii, has been obtained by means of experiments involving the intravenous injection into susceptible monkeys of 48 to 85 x 10(6) sporozoites derived from mosquitoes of a different species and source than employed previously. The development of these hypnozoites was traced from 3 days until 105 days after sporozoite inoculation, employing a sensitive immunofluorescence technique followed by restaining with Giemsa. From an average mean diameter of 4 micrometers at 3 and 5 days, uninucleate hypnozoites grow to 5 micrometers at 7 days, then persist with little change until at least 105 days after infection. Strong evidence for the viability of these persistent forms was obtained by treatment of a host monkey with primaquine, which eliminated all trace of hypnozoites present 2 weeks before. Examination of hepatic tissue from a monkey injected with sporozoites 36 and 40 hours earlier revealed rare uninucleate pre-erythrocytic forms of 2.5-micrometers diameter. These early forms were present in hepatocytes in a density only approximately 1/30th of that expected on the basis of numbers of pre-erythrocytic stages found in the same animal's liver 7 days after infection. Nevertheless, subinoculation experiments appeared to rule out the circulation as a vehicle for dissemination of any putative early intermediate hepatotropic forms from another site.

Detection of filarial antibodies in Malayan and Bancroftian filariasis by the indirect fluorescent antibody test, using different filarial antigens.

Indirect fluorescent antibody tests (IFAT) using Wuchereria bancrofti infective larvae as antigen had the highest positivity rates in detecting Malayan and Bancroftian filariasis as compared to IFAT using antigens prepared from 5 other animal filarial species, Brugia pahangi, Dirofilaria immitis, Dipetalonema viteae, Litomosoides carinii and Onchocerca gutturosa. This study also recommends the use of human filarioids as the source of antigen in serological tests. However, before B. malayi and especially W. bancrofti can be easily available from the common laboratory animals. B. pahangi seems to be a suitable source of antigen for use in serological tests for human lymphatic filariasis.

Observations on early and late post-sporozoite tissue stages in primate malaria. I. Discovery of a new latent form of Plasmodium cynomolgi (the hypnozoite), and failure to detect hepatic forms within the first 24 hours after infection.

Previous work in this laboratory has demonstrated the ability of the immunofluorescence technique to detect pre-erythrocytic stages of the primate malaria parasite, Plasmodium cynomolgi bastianellii, in hepatic tissue obtained as early as 48 hours after sporozoite inoculation. In an attempt to visualize still earlier post-sporozoite stages, hepatic tissue obtained from a rhesus monkey infected with 12,000,000 sporozoites was examined at 2, 12, 24, and 48 hours after inoculation, employing antisera reactive with both invertebrate and vertebrate stages of the parasite. Tissue was also obtained at 7, 50, 102, and 105 days after sporozoite inoculation, and was examined for adequacy of the hepatic infection and for the presence of late exoerythrocytic schizonts. Although a new, previously unrecognized, uninucleate latent stage of 5 micrometer diameter (the "hypnozoite") was detected among large maturing schizonts in the 7-day and later biopsies, no intrahepatic parasites were found in tissue taken at 24 hours or earlier, despite the presence of up to 61 7-day schizonts and eight hypnozoites per 5 X 8 mm section. Pre-erythrocytic forms again were detected at 48 hours, although in far smaller numbers than expected on the basis of the density of parasites at 7 days after infection. The significance of these observations is discussed in the context of previous negative findings.

Detection of antibodies in Brugia pahangi-infected cats by counter immunoelectrophoresis, indirect fluorescent antibody test and enzyme-linked immunosorbent assay.

In cats infected with Brugia pahangi, antibodies first appeared against the larvae (L3), then against the adults (L5) and the microfilariae (mf). Homologous antigens were better than antigens prepared from heterologous species (Dirofilaria immitis, Dipetalonema viteae, Litomosoides carinii and Onchocerca gutturosa) in detecting antibodies to B. pahangi in the infected cats by indirect fluorescent antibody test (IFAT). Metabolic products of L5, but not L3 or mf, of B. pahangi were antigenic and were used in the enzyme-linked immunosorbent assay (ELISA) for detection of antibodies. Using various homologous antigens, IFAT was found to be more sensitive than counter immunoelectrophoresis and ELISA in the detection of antibodies in the infected cats. The best antigen was cryosections of L3, with a positivity rate of 81%. However, using L3, L5 and mf antigens in IFAT, a total positivity of 97% was obtained.

Detection of circulating antigens and immune complexes in feline and human lymphatic filariasis.

Circulating worm antigens were detected in 61% to 81% of sera from Brugia pahangi -infected cats and in 0-93% of sera from humans with malayan of bancroftian filariasis by counter immunoelectrophoresis and a double antibody sandwich enzyme-linked immunosorbent assay, using rabbit antisera to B. pahangi adult worms. In some situations, both antigen tests were as sensitive as antibody tests. However, ELISA was likely to be affected by the presence of antiglobulins, such as rheumatoid factor, in the test sera. Only 10% to 22% of B. pahangi-infected cats (treated with drugs or not) had circulating immune complexes by the conglutinin-binding assay and no sera were positive by C1q-BA. A significantly higher percentage (56%) of B. malayi clinical sera was positive for immune complexes by either C1q- or conglutinin- binding assays as compared to other groups of B. malayi and Wuchereria bancrofti sera (6% to 14%).

A seroepidemiological survey in the Gezira, Sudan, with special reference to arboviruses.

A serological survey in the Gezira area of the Sudan confirmed that malaria and schistosomiasis were highly endemic. Of other parasitic infections amoebiasis was common but Toxoplasma was less than found in a previous survey. Poliomyelitis and measles infection were universal and there was an extremely high incidence of infection with hepatitis B. Of arboviruses infection with flaviviruses was frequent and more than with alphaviruses.