The American Journal of Tropical Medicine and Hygiene - Volume 29, Issue 1, 1980

Six-week-old rats infected with Plasmodium berghei developed a peak parasitemia of 55.2 ± 3.1% by day 15 of infection, followed by spontaneous resolution of the infection during a process referred to as crisis. Crisis was accompanied by the appearance in circulation of infected erythrocytes in which the parasites appeared abnormal (“crisis forms”). Rats splenectomized at different times during the crisis period experienced a sudden increase in parasitemia, with a marked decrease in the number of circulating crisis forms. Splenectomy resulted in a 100% mortality, whereas all control and sham-operated rats survived their infection. Although P. berghei is restricted to developing within young erythrocytes, our observations could not be explained by the effects of splenectomy on the number of circulating reticulocytes. Indeed, the reticulocytosis which accompanies crisis was unaffected by splenectomy. Our observations therefore suggest that crisis is a reversible process and, specifically, that the spleen is necessary for its maintenance.

Since an excess of blood group A in giardiasis has been repeatedly reported, we studied 190 patients with parasitologically confirmed giardiasis. Their blood group distribution did not differ from that of the Finnish population, and the statistically insignificant deviations were a surplus of group B and a shortage of group A. Among 85 participants of four travel groups which experienced an epidemic of giardiasis, the blood group distributions of the infected and the noninfected persons were not different. Thus, blood group A did not predispose to the acquisition of Giardia lamblia infection. To disclose an impact on the course of the disease, the patients were classified according to symptoms or duration of infection, but the ABO distributions did not differ from the expected. Our patients were adults, probably contracting giardiasis for the first time during a trip abroad, while the excess of group A has been reported in children in endemic areas.

None of the available chemical methods for disinfecting drinking water has ever been tested for its ability to destroy Giardia cysts. We tested the ability of six such methods to act against Giardia, using excystation as the criterion of viability. Two water qualities (cloudy and clear) and two temperatures (3 and 20°C) were tested. At 20°C, using cloudy and clear water, all of the methods proved completely effective. However, at 3°C, in cloudy water one method (“saturated” iodine) was less than completely effective, and in clear water four methods (bleach, Globaline, tincture of iodine and “saturated” iodine) failed to destroy all of the cysts. The failure of these methods appears to be related to either an insufficient halogen residual or contact time. This study underlines the importance of considering water temperature when employing halogen disinfection methods.

A method is described for purification of large quantities of Giardia muris trophozoites from the small intestine of the mouse by using density layer centrifugation and nylon fiber columns. Centrifugation of trophozoites obtained from the small intestine on Metrizamide®, specific gravity 1.10, followed by incubation on a nylon fiber column at 37°C for 120 min, yielded up to 15 × 106 viable purified trophozoites per infected mouse.

Cortisone and cyclophosphamide were found to suppress the protective effects of BCG in mice challenged with amastigotes of Leishmania donovani.

A fatal case of primary amebic meningoencephalitis (PAME) in a 35-year-old Nigerian Muslim farmer is described. The disease was contracted during ritual washing before prayers, which involved the sniffing of water up his nose to clean it. The water came from a man-made pond at his farm. The clinical presentation, isolation of the ameba from the cerebrospinal fluid and nasal passages, poor response to amphotericin B, and ultimate fatal outcome prove this to be a case of PAME. On the basis of its ability to grow at 42°C, morphology of the trophozoite, cyst, and flagellate forms, animal pathogenicity, and nuclear division the ameba was identified as Naegleria fowleri. Pathogenic N. fowleri were recovered from samples of water and soil from the pond. This represents the fourth proven case of PAME from northern Nigeria.

Extracts of Entamoeba histolytica produce rounding and agglutination of mammalian cells in tissue culture. This effect is inhibited or reversed by serum, by the serum glycoprotein, fetuin, or by N-acetyl-D-galactosamine. Concanavalin A produces a similar cytotoxic effect that is blocked or reversed by α-methyl mannoside. These properties suggest that the amebal “toxin” has a lectin-like activity.

We report a case of pulmonary strongyloidiasis which occurred after high-dose corticosteroid therapy. Our patient responded very well to treatment with thiabendazole, despite the fact that the steroids were continued throughout his entire hospital course. Further complications included pseudomonas meningitis and Klebsiella pneumoniae pneumonia, both of which resolved with appropriate treatment.

Tissue culture fluid NCTC 135 (Hank's base) was compared to water and to saline as incubation media for the detection of microfilariae of Onchocerca volvulus in skin snips. NCTC 135 allowed detection of significantly more positive persons than did water (P < 0.001) or saline (P < 0.05) when two snips per person were incubated for periods of 0.5 or 24 hours. In addition, snips containing microfilariae were incubated in NCTC 135 or in saline and the number of emerged microfilariae was determined at various intervals of time up to 24 hours. After incubation, snips were either fixed in 10% formalin, serially sectioned, and the microfilariae counted, or they were digested in collagenase solution to free unemerged microfilariae. Of the total number of microfilariae present in the snips, 43.9% ± 18.5, 80.2% ± 22.2, 83.0% ± 19.5, and 85.3% ± 18.0 had emerged by 0.5, 4, 8, and 24 hours of incubation, respectively. Of the microfilariae that remained in the skin after incubation, most were located deep in the dermis.

The prevalence of Mansonella ozzardi in the Comisaría del Vaupés of eastern Colombia was investigated as part of an extensive study of human filariasis in Colombia. Three hundred and forty-seven individuals from various parts of Vaupés were examined. The overall infection rate for M. ozzardi was 49%, but the distribution of the parasite was not uniform throughout the Comisaría. Microfilariae were found in both venous blood samples and skin biopsies of infected individuals. The rate of infection was 55% for males and 42% for females, and infection rates tended to increase with age. Microfilarial levels in 20 mm3 thick blood films were generally low, with 88% of the positive films having less than 50 microfilariae.

Brugia malayi and B. Pahangi microfilariae from gerbil intraperitoneal infections were inoculated into the thorax of male and female Toxorhynchites amboinensis and developed into third-stage larvae as early as 11 days. In a comparative study with Aedes togoi fed on microfilaremic gerbils, third-stage larvae were found at 10 days. Some third-stage larvae of B. malayi inoculated into gerbils developed to advanced stages. Third-stage larvae of Wuchereria bancrofti were recovered in low numbers from Tx. amboinensis and Tx. aurifiuus inoculated with microfilariae recovered from human blood by membrane filtration. Development of all filarial species was similar in both male and female mosquitoes. Toxorhynchites species are plant feeders and therefore reduce the hazards of laboratory transmission of pathogenic agents. Because of their large size, manipulations with this mosquito species are easy and the size allows for a larger inoculum to be used. This group of mosquitoes should develop into useful laboratory vectors for the transmission of arthropod-borne diseases.

Two families, comprising 11 individuals in the toxemic form of schistosomiasis mansoni, infected in Belo Horizonte, Brazil were treated. Parasitological cure was obtained in 5 (45%) of the patients after a single oral dose of oxamniquine (Mansil®), 20 mg/kg body weight. No significant side effects were observed. To evaluate the possibility of resistance to the drug, cercariae collected from Biomphalaria glabrata infected with miracidia from eggs obtained from three of the individuals not cured were studied. Mice infected with these three strains were cured after a single oral dose of oxamniquine. It is suggested that research be continued with other therapeutic schedules and perhaps other, more potent, drugs.

Physiological responses to physical exercise were measured in 203 Sudanese villagers and cleaners of irrigation canals in order to assess the effect of Schistosoma mansoni infection on work capacity. The investigations were carried out on economically active males (18–45 years old) of Gezira villages, where no mass antischistosomal treatment or molluscicidal applications had been made. Before the physiological tests, all subjects received antimalarial prophylaxis (chloroquine phosphate). There was a statistically significant difference (P < 0.002) in maximum aerobic power output (O2 max) between villagers and canal cleaners amounting to 18%. There was no such difference between noninfected villagers and villagers with light infection, but the impairment in physical working capacity became manifest when the pattern of intensity of infection changed from light (<1,000 eggs/g) to very heavy (>2,000 eggs/g). Age, body weight, stature, lean body mass, leg muscle volume, and nutritional status were similar for canal cleaners and villagers. However, the villagers had a significantly higher (P < 0.001) mean hemoglobin concentration compared to that of canal cleaners which would at least partly explain the difference in O2 max. The results of this study provide quantitative evidence of the adverse effect of high levels of S. mansoni infection on physical working capacity.

In vivo microscopy was used to examine the dynamics of Schistosoma mansoni schistosomule and egg migration in an attempt to clarify some of the controversial facets. Schistosomule migration in the organs was found to be restricted to the vascular system. The migration of the youngest schistosomules was a passive process, while the migration of schistosomules with pigment in their ceca was an active one. In the liver, schistosomules with blood in their ceca were only found in the intrahepatic branches of the portal system. In these vessels the worms fed facing the direction of blood flow. The consequences of their presence in these venules were an interference with blood flow not only in these vessels but also in the adjacent sinusoides, which caused dilatation and sacculation of the sinusoides with margination of leucocytes, deposition of blood pigment in Kupffer cells and, finally, stasis. This resulted in necrosis of the surrounding hepatocytes, whereupon leucocytes and macrophages invaded the site producing a midzonal necrosis. Eggs in the mural venules of the intestine were always found in venules with a diameter greater than 60 µm. When single eggs were present in venules with a diameter almost equal to the diameter of the egg, the vessel sacculated at this site. Such eggs transited through the wall without deformation of the egg and without hemorrhage. In contrast to single eggs, clusters of eggs compromised blood flow, resulting in necrosis of the wall and thereby liberating the eggs in the parenchyma for migration. In the parenchyma the eggs were first parallel to the lumen of the intestine, and were present throughout the various layers of the intestinal wall with the exception of the villi, in which they were never found.

Niridazole was incorporated into silicone rubber implants to investigate the potential of a sustained release of the drug in the therapy of murine schistosomiasis mansoni. The infected animals (200 cercariae for 6 weeks) were randomly divided into three groups: one group received silicone rubber implants containing 50% by weight niridazole; a second group received blank silicone rubber implants with no drug; and the third group received no implants. Mortality 4 weeks later was in excess of 80% for animals with no implants or with the blank silicone rubber implants. In contrast, 10% mortality was observed in the mice receiving the niridazole-silicone rubber implants over a 10-week period. The worm burden in the niridazole-silicone rubber implant group was reduced at 10 weeks post implantation by 77%.

Circulating Schistosoma mansoni soluble antigens (CSA), circulating anti-S. mansoni antibodies (CAb), and immune complexes (CIC) were studied in three groups of African patients living in the same area. The first two groups were composed of 26 S. mansoni-infected mothers and their 26 uninfected newborn children. The third group included 13 men and 10 non-pregnant women who were also infected with S. mansoni. CSA were quantified by using a solid phase sandwich radioimmunoassay, which was shown to be sensitive, reproducible, and S. mansoni-specific. CAb were studied by indirect hemagglutination. CIC evaluations were performed by using the Clq binding test. A high correlation was shown between the CSA levels in sera from infected mothers and from the umbilical cord of their newborn children, indicating that CSA are probably transferred through the placenta. CSA levels in mothers were significantly higher than in the third group, in which no difference was found between men and women. On the other hand, CAb and CIC were significantly higher in the third group than in the group of mothers, indicating that CSA levels may be modulated by the immune response of the host.

Sera from patients with acute or early and chronic schistosomiasis were examined for IgG, IgM, and IgE antibody by an enzyme-linked immunosorbent assay technique, using soluble egg antigen from Schistosoma mansoni. Cercarial/adult IgG antibody ratios were determined, using soluble cercarial and adult worm antigens. Sera with cercarial/adult ratios indicative of acute or early schistosomiasis also contained specific IgM antibodies. Schistosome IgE antibody was found in sera from patients with acute schistosomiasis, but in only 1 of 10 sera from patients with chronic schistosomiasis. The inability of ELISA to detect IgE antibodies in chronic sera indicates that it may be a relatively insensitive measure of IgE antibodies in those patients with chronic schistosomiasis.

A wealth of epidemiological information available on bilharziasis in Puerto Rico made it possible to trace historical trends in the distribution of the disease. From a few scattered foci present in the early 20th century, the extent and intensity of the disease increased on the south coast after construction of sugar irrigation systems in 1914. After 1953 this major endemic area was brought under control while a new endemic area was developing in the eastern portion of the island, due to creation of rural communities known as “parcelas.” The increased transmission caused by the parcelas had been counteracted in other parts of the island after the Second World War by the widespread contruction of water supply systems and by filling of wetlands and channelization of streams on the growing suburban fringes of the major cities. Finally, an expanded snail control program of the 1970s covered most of the newer foci created by the parcelas, except for a small area on the north coast, east of San Juan. By 1976 only about 100,000 persons carried the parasite, mostly children with asymptomatic infections. They lived primarily in the northeastern municipalities, as well as scattered remnants throughout the classical endemic areas. Complete control of the disease could be accomplished in a few years, finally breaking the connection between sugar and snails in Puerto Rico.

An enzyme-linked immunosorbent assay (ELISA) was adapted for the indirect serological measurement of anti-Echinococcus antibodies in human hydatid disease. Both the tube method and the microtitration procedure were used successfully. However, the tube test with a purified hydatid fluid fraction appears to be the method of choice. ELISA results are comparable to those found in the indirect hemagglutination test and with the agar gel methods (double diffusion and immunoelectrophoresis), but false positive results were observed with the sera of patients with schistosomiasis or liver cirrhosis. ELISA has proved to be a sensitive quantitative procedure for the serodiagnosis of human echinococcosis, even though it has not been shown in our study to be more sensitive than the classical serological procedures such as indirect hemagglutination. It can be concluded that ELISA should be considered not as an alternative but as a useful addition to the range of immunodiagnostic tests available for serodiagnosis of hydatid disease.

In this study we assess the degree of prolonged bacteriostasis of Mycobacterium leprae after temporary exposure to ethionamide or thiacetazone, and relate this to their efficacy when administered intermittently to mice with experimental leprosy infections. The results show that temporary exposure of M. leprae to either of these drugs results in a prolonged bacteriostatic effect, but that efficacy is rapidly lost as the interval between doses is increased. Using the mouse foot pad system, growth of M. leprae is not inhibited by thiacetazone when the frequency of administration is less than three times weekly. When ethionamide is administered once weekly, growth of M. leprae is inhibited but bactericidal activity is lost. When ethionamide is administered in combination with continuous dapsone therapy, either continuously or three times weekly, the bactericidal activity of the drug combination is greater than when either drug is administered alone. However, when ethionamide is administered once weekly in combination with continuous dapsone treatment, the bactericidal effect is identical to that when dapsone is given alone: that is, ethionamide makes no contribution to the combination.