A malaria outbreak due to Plasmodium malariae on the Island of Grenada.

An outbreak of Plasmodium malariae malaria occurred in Grenada some 16 years after the end of a malaria eradication campaign, probably due to renewal of transmission from recrudescent cases. Serological studies were used in addition to blood film surveys in defining the outbreak, and their value in such surveillance situations is emphasized.

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.

Humoral immune responses in human hepatosplenic schistosomiasis mansoni.

The development of hepatosplenic schistosomiasis in humans cannot always be related to the intensity of infection. A study was designed to identify different humoral immunologic responses to Schistosoma mansoni in patients with and without hepatosplenic disease. Twenty-four patients with active hepatosplenic disease were closely matched for age, sex, and fecal egg counts with twenty-four patients with only intestinal disease. A serum sample from each of these patients was tested for antibodies to the major soluble egg antigen (MSA1) by radioimmunoassay, for total and IgM antibodies to egg and worm antigenic preparations by ELISA, and for its ability to suppress antigen stimulated lymphocyte blastogenesis. No difference was found using these assays between the hepatosplenic and the intestinal schistosomiasis patients.

House construction, triatomine distribution, and household distribution of seroreactivity to Trypanosoma cruzi in a rural community in northeast Brazil.

Household distribution of seroreactivity to Trypanosoma cruzi in inhabitants was analyzed in relation to house construction and the distribution of Panstrongylus megistus, the principal domestic vector of Chagas' disease in a rural area in northeast Brazil. No children residing in mud-brick houses were seroreactive to T. cruzi. The highest rates of seroreactivity occurred in residents of unplastered mud-stick houses, and were twice as high as those found in persons living in mud-brick houses or plastered mud-stick houses. Two-thirds of seroreactive children in this area resided in unplastered mud-stick houses. Over 90% of the P. megistus infestations were found in mud-stick houses. Mud-brick houses had the lowest infestation rates of P. megistus and the lowest household rates of seroreactivity to T. cruzi.

Trypanosoma cruzi infection in dogs and cats and household seroreactivity to T. cruzi in a rural community in northeast Brazil.

The prevalence of Trypanosoma cruzi parasitemia as determined by xenodiagnosis on domestic dogs and cats was correlated with household rates of seroreactivity to T. cruzi and household Panstrongylus megistus infestation in a rural area in northeast Brazil where P. megistus was the only domiciliary triatomine vector. T. cruzi infection was present in about 18% of domestic dogs and cats. Two-thirds of seroreactive children below age 10 resided in houses with T. cruzi-infected animals. In houses with a T. cruzi-infected dog or cat, as well as at least one infected P. megistus, the household rate of seroreactivity to T. cruzi was five times greater than in houses with non-infected domestic animals and no infected triatomine vectors. Domestic dogs and cats are important reservoirs of T. cruzi in an endemic area where P. megistus is the only domiciliary triatomine vector.

The epidemiology and household distribution of seroreactivity to Trypanosoma cruzi in a rural community in northeast Brazil.

The prevalence rates and household distribution of seroreactivity to Trypanosoma cruzi by complement fixation (CF) and indirect immunofluorescent antibody methods were determined in a population of 1,087 persons living in a rural area endemic for Chagas' disease in northeast Brazil. There was a gradual rise in the rate of seropositivity to 60% by age 20. Between ages 20 and 55 the prevalence rate remained at about 60%, but declined thereafter. The decline in the older age groups was not accompanied by a fall in geometric mean titer, suggesting that the decline might better be explained by an increased mortality among those seropositive than by a decrease in CF reactivity associated with age. There was variation in the rates of seropositivity in children among the geographic subunits, but the rates among adults were fairly uniform. Household clustering of seropositivity was demonstrated when both household size and age distribution were taken into account. The presence of a seropositive child less than 5 years of age was a good indicator of a household with a high rate of seropositivity; screening for young seropositive children might be a useful tool to locate high risk households. Seropositive children in households where the mother was seropositive but the father seronegative were significantly younger than seropositive children in households where the father was seropositive but the mother seronegative even though the age distribution and the overall rate of seropositivity in both groups of children were similar; thus, conversion to seropositivity earlier in life in children of seropositive mothers may not be due solely to increased exposure, but may indicate that the immunologic response in such children differed from that of children from seronegative mothers.

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.

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.

Chagas's Disease in the Amazon Basin: 1. Trypanosoma cruzi infections in silvatic mammals, triatomine bugs and man in the State of Pará, north Brazil.

A total of 1,197 wild animals from Pará State north Brazil, were examined for haematozoa. Trypanosoma cruzi-like parasites were found in 13 different species, and were particularly common in a variety of marsupials (Didelphidae), porcupines (Coendou spp.), armadillos (Dasypus novemcinctus) and coatimundis(Nasua nasua). Three human infections are reported, making a total of seven autochthonous cases of Chagas's disease from Pará since the first were described in 1969. A serological survey of 5,319 inhabitants from the Belém suburbs revealed 14 positive reactions with immunofluorescent antibody titres greater than 1:64, and 15 equivocal reactions at 1:16. No evidence was found of silvatic species of triatomine bugs (Hemiptera: Reduviidae) colonizing houses, but occasional infected specimens of Panstrongylus geniculatus and Rhodnius pictipes were found in suburban houses, near the forest. Human infection is considered to be silvatic in origin. Chagas's disease could become endemic in the Amazon Basin if silvatic triatomine bugs were able to adapt to a domestic habitat: the real danger, however, is in the possible importation of already domiciliated vector-species along the newly opened highways, from other endemic regions of Brazil. Other Trypanosoma species were recorded in a variety of wild animals. Haemogregarines were found in some marsupials and rodents, and piroplasms in marsupials and a single armadillo.

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.

Experimental Trypanosoma cruzi infection in rhesus monkeys 111. Electrocardiographic and histopathological findings.

In five rhesus monkeys surviving 'Peru strain' or 'strain 7' Trypanosoma cruzi infection for six to eight years, positive xenodiagnosis results and high indirect fluorescent antibody titres (4096 - 65536) persisted until the animals were killed. Abnormal electrocardiograph patterns in two monkeys (H and K) were possibly compatible with myocardial damage. Histopathological changes attributable to T. cruzi infection were minor in four monkeys but severe in one (R). In this animal, infected with what was judged previously to be the less virulent of the two T. cruzi stocks used ('strain 7'), there was severe myocarditis, with myofibre degeneration, and lesions of the oesophagus. Elevated serum levels of five enzymes were not detected in any of the chronically infected monkeys.

A strain of Plasmodium vivax characterized by prolonged incubation: the effect of numbers of sporozoites on the length of the prepatent period.

The North Korean strain of Plasmodium vivax was characterized by its extraordinarily prolonged incubation period in certain circumstances. It was clearly demonstrated by quantitative observations that the phenomenon may be elicited by the inoculation of small numbers of sporozoites. After the intradermal inoculation of 10 or 100 sporozoites, the incubation period was delayed for periods varying between 262 and 628 days; after u,000 sporozoites, with one exception, the same delay occurred; after 100,000 sporozoites, the incubation period was always of normal duration (13--16 days). Two laboratory-acquired infections in workers who had taken a prophylactic drug showed incubation periods of 315 and 329 days, respectively. Various theories for the phenomenon of prolonged prepatent periods are examined, and the most satisfactory one is based on the presumed existence of two populations of sporozoites in P. vivax. In temperate strains, sporozoites requiring long prepatent periods (LPP) for development are present in great excess over a much smaller proportion of sporozoites characterized by short prepatent periods (SPP); thus small doses will elicit the phenomenon, though doses of over 1,000 sporozoites will mask the effect as the few SPP sporozoites will produce an infection with a normal (i.e. short) prepatent period. In tropical strains, the relative proportions are different, perhaps in equal numbers, and even in small doses some SPP sporozoites will be present and normal prepatent periods should ensure whatever the dosage."

Experimental Trypanosoma cruzi infections in rhesus monkeys. II. The early chronic phase.

Information on the acute and early chronic phases of infection with Trypanosoma cruzi in eight rhesus monkeys is reported with particular reference to the pattern of subpatent parasitaemia and serology. Xenodiagnosis was superior to animal inoculation and blood culture in its capacity to detect subpatent parasitaemia. Each monkey showed an individual, relatively constant pattern of this not related to the nature of the inoculum. Levels of indirect fluorescent and indirect haemagglutinating antibodies remained elevated during a year of observations. One monkey died with a megaoesophagus. Another monkey after challenge with a heterologous strain by orbital inoculation failed to develop Romana's sign and showed no change in serum antibody levels or degree of xenopositivity.

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.

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%).

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.