Does the snail Melanoides tuberculata have a role in biological control of Biomphalaria pfeifferi and other medically important African pulmonates?
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Animals↗
Biomedical subjects
D K Koech
Publications and source records attributed to D K Koech.
Predation of Biomphalaria and non-target molluscs by the crayfish Procambarus clarkii: implications for the biological control of schistosomiasis.
The North American crayfish Procambarus clarkii was examined under laboratory conditions for its ability to prey on Biomphalaria pfeifferi and B. glabrata, molluscan intermediate hosts of human schistosomiasis, and other, non-target gastropod species. Both male and female adult crayfish significantly reduced survival of neonate snails, even though alternative animal and plant foods were both available. In subsequent experiments, no differences in snail consumption were detected, for either adult or juvenile crayfish, in the presence or absence of a plant food alternative. Both adult and juvenile crayfish were able to consume small (2.5 mm) and large (17.5 mm) B. glabrata, suggesting that no size refuge from predation exists. Both adult and juvenile crayfish consumed Biomphalaria egg masses, although this consumption was significantly greater for juveniles. Procambarus clarkii adults were unable to consume substantial numbers of the relatively thick-shelled prosobranch snails Pila ovata and Lanistes carinatus. Crayfish did consume a third prosobranch, Melanoides tuberculata, and the pulmonate snail Physa acuta, but at a lower rate relative to consumption of Biomphalaria. Physa acuta, itself of North American origin, responded to the presence of crayfish by rapidly leaving the water and thereby avoided predation. Implications of these results for the biological control of schistosome-transmitting snails in East Africa are discussed.
Animals↗
Cellular and humoral immune responses in a population from the Baringo District, Kenya to Leishmania promastigote lipophosphoglycan.
In a cross-sectional house-to-house study in a leishmaniasis-endemic area in Kenya, the cellular and humoral immune response to Leishmania lipophosphoglycan (LPG) was determined. Clinical data, peripheral blood mononuclear cells, and plasma were obtained from 50 individuals over the age of eight years. Lymphoproliferation and interferon-gamma (IFN-gamma) production by these cells were examined. It was shown that cells from all six individuals in the population with a history of kala-azar responded to LPG in the lymphocyte proliferation assay, and four of these six responded in the IFN-gamma assay. In contrast, cells from 12 of 44 individuals from the study area with no history of kala-azar and none of the five Danish control samples responded to LPG. Antibodies against LPG were detected by enzyme-linked immunosorbent assay in 45 of 50 plasma samples. Our findings clearly show that mononuclear cells from kala-azar patients cured of infection were able to respond to the LPG preparation. The finding of a specific cellular immune response to LPG in 12 of 44 individuals with no history of kala-azar is consistent with previous epidemiologic studies, in which it has been shown that a proportion of L. donovani infections run a subclinical course. The high frequency of individuals with antibodies against LPG might indicate that a majority of the population had been exposed to the parasite.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
In vitro experimental antileishmanial potential of ethylenediamine tetraacetic acid, disodium salt.
Leishmania donovani promastigotes (NLB 065) were treated to various concentrations of ethylenediamine tetraacetic acid (EDTA), disodium salt for 7 days. Concentrations of up to 1.0 mg/ml produced no significant reduction in the population of Leishmania promastigotes cultured in RPMI 1640 medium supplemented with 15% foetal calf serum and incubated at 27 degrees C (P greater than 0.05). Concentrations between 0.05 and 0.1 mg/ml EDTA did not significantly affect the viability of Balb/c mouse peritoneal macrophages (P greater than 0.05) whereas those equal to or above 0.2 mg/ml were severely toxic to macrophages (P less than 0.05; n = 8). Leishmania parasites engulfed in mouse peritoneal macrophages were treated to various concentrations of ethylenediamine tetraacetic acid (EDTA) disodium salt. The higher the EDTA concentration within the acceptable toxic levels for macrophages (less than or equal to 0.1 mg/ml), the higher was the rate at which parasites were cleared (p less than 0.05). The length of time in days within which infected macrophages were treated contributed significantly to a decline in the level of parasite-loads (P less than 0.05; n = 10). Analysis of mean metal ion values in mg/1 using atomic absorption spectrometry revealed that the levels of calcium, magnesium, and iron were virtually unchanged in the supernatant of variant culture experiments (P greater than 0.05). The level of manganese was higher in ethylenediaiene tetraacetic acid (EDTA), disodium salt-treated cultures as compared to the control (P less than 0.05; n = 20).(ABSTRACT TRUNCATED AT 250 WORDS)
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Use of beef extract as a diluent in direct agglutination test for visceral leishmaniasis.
Direct Agglutination Tests (DAT) have been developed for sero-diagnosis of visceral leishmaniasis (VL). The objective of this study was to find a more suitable diluent for serum dilution in a Direct Agglutination Test. 1% of beef extract (BEX) was used as a diluent in the Direct Agglutination Test; 1% foetal bovine serum (FBS) and 0.2% gelatine (Gel) were included for comparison as alternative diluents. Serum from VL patients, individuals suffering from hydatidosis, syphilis and from healthy adult Kenyans was used as control. Beef extract was found to be easy to handle, less expensive and results comparable to those obtained from the other diluents.
Agglutination Tests↗
Consumption of Biomphalaria glabrata egg masses and juveniles by the ampullariid snails Pila ovata, Lanistes carinatus and Marisa cornuarietis.
Lanistes carinatus and Pila ovata from Kenya and Marisa cornuarietis from the Dominican Republic were examined for their ability to consume egg masses and juveniles of Biomphalaria glabrata (M line strain) under laboratory conditions. Adults of all three ampullariid species consumed all egg masses presented to them over a five day period of observation. Juvenile P. ovata consumed significantly more egg masses than juveniles of M. cornuarietis or L. carinatus. Both adult and juvenile ampullariids generally ate more egg masses when maintained under a temperature regime (25-32 degrees C) approximating conditions in coastal Kenya than at 13-25 degrees C which approximates the temperature regime near Nairobi, Kenya. Egg masses attached to floating 'refugia' were not attacked, apparently reflecting the difficulty experienced by ampullariids in reaching free-floating objects. Adults of each ampullariid species ate approximately 25% of all lariids in reaching free-floating objects. Adults of each ampullariid species ate approximately 25% of all 1.5 +/- 0.5 mm B. glabrata juvenile snails presented to them. P. ovata adults consumed significantly more 3.0 +/- 0.5 mm juveniles than adults of the other two species. B. glabrata egg masses and juveniles were consumed even though lettuce was continually present in experimental aquaria. Implications of these results for biological control studies in East Africa are discussed.
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Growth of Biomphalaria glabrata populations in the presence of the ampullariid snails Pila ovata, Lanistes carinatus and Marisa cornuarietis.
Adults of three ampullariid species were examined for their ability to affect the population growth of Biomphalaria glabrata (M line strain) under laboratory conditions in which food (lettuce) was supplied ad libitum over an eleven week interval. Lanistes carinatus and Pila ovata were obtained from Kenya, and Marisa cornuarietis originated from the Dominican Republic. The presence of either 3 or 9 L. carinatus or 3 M. cornuarietis per 40 l aquarium did not reduce the population size of B. glabrata below levels attained in control aquaria lacking ampullariids. The presence of 9 M. cornuarietis adults significantly reduced B. glabrata populations by week 10 of the experiment. Presence of 3 or 9 P. ovata per aquarium significantly reduced B. glabrata numbers below control levels starting at week four of the experiment. Aquaria with 9 P. ovata were observed to have fewer B. glabrata egg masses than control aquaria, but the number of egg masses observed was not significantly reduced in aquaria with 3 P. ovata or with 3 or 9 L. carinatus or M. cornuarietis. However, the presence of 3 or 9 adults of each ampullariid species resulted in a significant increase in the percentage of such egg masses that disappeared prior to expected hatching date and that were presumed to have been consumed. The results of his laboratory study suggest that further investigation of the role of ampullariids as biological control agents for pulmonate snails in sub-Saharan Africa should focus on P. ovata.
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Plasmodium falciparum sensitivity to erythromycin and 4-aminoquinoline combinations in vitro.
Although erythromycin has been reported to be active against Plasmodium falciparum in vitro and P. berghei in vivo and in vitro when given alone or with chloroquine, it has been difficult to demonstrate a beneficial effect for the combination of erythromycin and chloroquine when used for the treatment of P. falciparum infections in humans. We developed a seven-day test of parasite sensitivity to a 4-aminoquinoline and erythromycin combination in vitro. Eight isolates of P. falciparum from the Kenyan coast were culture-adapted and exposed to erythromycin with chloroquine or with amodiaquine. The interaction of the drugs was evaluated by plotting the concentration of each drug needed to inhibit parasite growth. In seven isolates the combination of chloroquine and erythromycin was antagonistic; one isolate showed slight synergy The combination of amodiaquine and erythromycin was synergistic in three isolates but antagonistic in five. An antagonistic interaction may explain why erythromycin does not enhance chloroquine treatment of malaria in vivo in Kenya.
Aminoquinolines↗
Species composition of the Anopheles gambiae complex (diptera: Culicidae) at two sites in western Kenya.
At two sites in the Kisumu area of western Kenya, the species composition of the Anopheles gambiae complex was determined by analysis of ovarian polytene chromosomes. Of 1,915 females, 26.1% were An. arabiensis Patton and 73.9% were An. gambiae Giles; one arabiensis x gambiae hybrid was identified. No major differences in the proportions of An. arabiensis and An. gambiae were observed between sites or between years. The ratio of An. arabiensis/An. gambiae was 6.7:1 (n = 231) in cow-baited traps, 0.2:1 (n = 1,525) in indoor resting samples, and 0.5:1 (n = 145) in all-night human bait catches. The proportion of An. arabiensis decreased progressively from 50.0% to 8.3% (n = 1,129) during 11 wk from September to November 1987; this change was correlated negatively with night temperature and positively with temperature range. In cow-baited traps, 97.4% (n = 194) of An. arabiensis were cow-fed and 95.8% (n = 1,054) of An. gambiae from indoor resting collections were human-fed. In indoor collections, 37.2% (n = 215) of An. arabiensis were cow-fed and 23.1% (n = 26) of An. gambiae from cow traps were human-fed. This demonstrates post-blood-feeding endophily by An. arabiensis and suggests post-blood-feeding exophily by An. gambiae. Malaria infection rates were higher for An. gambiae than for An. arabiensis by a ratio of 3:1 in 1986 (by Plasmodium falciparum ELISA) and 2.3:1 in 1987 (by dissection). Despite the higher proportion of infective An. gambiae, both species in this area serve as efficient vectors through their remarkably stable contact with the human population as demonstrated by their blood feeding and resting behavior.
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Plasmodium species identification by ELISA for sporozoites removed from dried dissection slides.
This study tested the feasibility of identifying salavary gland sporozoites to species by Plasmodium falciparum ELISA by drying them on slides or in vials. The glands were dissected from Anopheles gambiae Giles s.l. and An. funestus Giles collected in western Kenya. In 119 gland infections containing a geometric mean of 1,222 sporozoites, a mean of 72.5% of sporozoites were removed in 60 microliters saline from slides at the time of dissection. Each of the 119 samples was divided into three 18 microliters aliquots. Subsamples were stored at -70 degrees C, dried in vials, or dried on a microslide. When tested by Plasmodium falciparum ELISA, positive reactions were observed in 86.6% of frozen samples, 70.6% of samples held dry in vials, and 50.4% of samples held dry on microslides for 1 mo. Of 90 gland infections where coverslips were removed and slides were left to dry for 1 mo before adding blocking buffer, 81.1% were positive for P. falciparum. This was not significantly different from either frozen gland samples (where 85.5% of 392 infections were identified or frozen gland plus corresponding thorax samples where 86.2% of 160 samples were identified). In malaria field studies, where it is not always practical to freeze samples, sporozoites from dissected mosquitoes can be preserved adequately for ELISA identification by simply removing coverslips and drying dissection slides.
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Potassium supplementation versus bendrofluazide in mildly to moderately hypertensive Kenyans.
Eighty-four consecutive black patients who had confirmed but untreated hypertension participated in a double-blind randomized clinical trial involving potassium supplement (64 mmol/day) versus bendrofluazide (10 mg/day). Diastolic blood pressure (DBP) of the 42 patients receiving potassium supplementation (group A) decreased from a mean (+/- SD) of 108 +/- 3 to 88 +/- 4 mm Hg (p less than 0.001; paired t test) after 28 weeks of medication. DBP of the 42 patients receiving bendrofluazide (group B) decreased from a mean of 108 +/- 2 to 84 +/- 4 mm Hg (p less than 0.001; paired t test). There was no statistically significant difference between the magnitude of decrease in DBP in group A and B patients (unpaired t test). No clinical, biochemical, or ECG abnormalities occurred in group A patients. Eight group B patients showed hyperuricemia; 4 patients in the same group had hyperglycemia and 3 other patients had hypokalemia. The results support the notion that potassium supplementation may be an effective therapeutic approach to mildly hypertensive blacks.
Adult↗
Quantitation of malaria sporozoites in the salivary glands of wild Afrotropical Anopheles.
The number of malaria sporozoites in the salivary glands was determined microscopically for 1137 wild, naturally infected Anopheles from western Kenya. Infective Anopheles gambiae Giles sensu lato (n = 874) contained a geometric mean (GM) of 962 sporozoites and An.funestus Giles (n = 263) contained 812. No significant differences were detected in geometric mean numbers of sporozoites between species, collection techniques or sites. Of the infective An.gambiae, 1.7% (15/874) contained more than 41,830 sporozoites, the maximum observed for An.funestus. Microscopic techniques were found to be more sensitive than enzyme-linked immunosorbent assays (ELISA) for detecting low-grade sporozoite infections in salivary glands. Salivary gland sporozoites from 83.6% of the 1137 gland infections were identified by ELISA as either Plasmodium falciparum Welch (n = 910), P.ovale Stephens (n = 7), P.malariae Grassi & Feletti (n = 3) or mixed (n = 30). The 187 gland infections which could not be identified by ELISA contained significantly fewer sporozoites (GM = 242) than those which could be identified (GM = 1200).
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Quantitation of malaria sporozoites transmitted in vitro during salivation by wild Afrotropical Anopheles.
The malaria transmission potential of wild, infective Anopheles from western Kenya was evaluated by determining the number of sporozoites transmitted in vitro by salivation when their mouthparts were inserted into capillary tubes containing either sucrose or blood. With sucrose, 86.6% of 102 infective Anopheles transmitted a geometric mean (GM) of 3.84 sporozoites (range 1-34). With blood, 23.1% of 104 infective Anopheles, tested on the day of collection, transmitted a GM of 2.30 sporozoites (range 1-117). For Anopheles held 5 days postcapture before testing with blood, 53.6% of 56 transmitted a GM of 6.04 sporozoites (range 1-420). Transmitting Anopheles contained significantly more salivary gland sporozoites than non-transmitters. No significant differences were detected between Anopheles gambiae Giles sensu lato and Anopheles funestus Giles in sporozoite transmission by individuals with sporozoites in their salivary glands. Sporozoites were detected microscopically in the salivary duct from heads in 80.3% of 117 infective Anopheles (GM = 11.2, range 1-71). Sporozoite detection in mosquito heads by ELISA was 25% less efficient than microscopic detection. Over 98% of the infective Anopheles transmitted less than twenty-five Over 98% of the infective Anopheles transmitted less than twenty-five sporozoites. Transmitted sporozoites represented only about 3% of the total sporozoites in the salivary glands suggesting that sporozoite transmission may be restricted to sporozoites in the salivary duct at the time of feeding. Results are discussed in relation to anti-sporozoite vaccine development.
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Activation of human T lymphocytes by Leishmania lipophosphoglycan.
This study describes Leishmania antigen-induced activation of lymphocytes isolated from Kenyan donors, previously treated for visceral leishmaniasis, and from Danish and Kenyan controls. Peripheral blood mononuclear cells (PBMC) from cured Kala-Azar patients proliferated and produced Interferon-gamma in vitro in response to lipophosphoglycan (LPG) isolated from Leishmania major. The proliferative response was mainly due to activation of CD2-positive T cells. PBMC from controls did not respond to LPG, but to sonicates prepared from both L. major and L. donovani promastigotes. The surface glycoprotein GP 63 failed to activate PBMC from any of the donors tested. These results show that the individuals cured from visceral leishmaniasis had expanded T-cell clones recognizing LPG, conceivably as a result of Leishmania infection. The LPG preparation was without detectable protein contamination. Thus, the results suggest that human T lymphocytes can respond to glycolipid antigens.
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Concurrent infection with Leishmania donovani and Leishmania major in a Kenyan patient: clinical description and parasite characterization.
Leishmania isolates aspirated a few months apart from the spleen of an indigenous adult male kala-azar patient from Baringo District, Kenya, were biochemically characterized and compared. The patient lived within a dual focus of L. donovani kalazar and L. major cutaneous leishmaniasis. A primary Leishmania isolate from splenic aspirates was cryopreserved (NLB-294). The patient was treated with sodium stibogluconate for kala-azar and discharged. Three months later, he had clinical relapse and returned for retreatment. During his second visit, the patient participated in a diagnostic study in which urine and nasopharyngeal samples were cultured for leishmaniasis. Urine, nasopharyngeal, and splenic samples were positive for Leishmania. Secondary isolates from splenic (NLB-294-I) and urine (NLB-318) cultures were cryopreserved and characterized by cellulose acetate electrophoresis (CAE) using 20 enzymes. Whereas the urine isolate was typed as L. donovani, the splenic aspirate culture revealed a mixed infection with L. donovani and L. major. The primary isolate (NLB-294) was then characterized and also showed a mixed infection. To exclude the possibility of protein post-translational modifications in electrophoretic assays, the primary and secondary isolates were grown and processed under identical cultural and lysis conditions, and compared using CAE. The results were identical to the first electrophoretic assays showing mixed promastigote banding patterns. Stationary-phase promastigotes of the secondary splenic isolate (NLB-294-I) inoculated subcutaneously, intraperitoneally, and intracardially into Syrian hamsters and BALB/c mice produced both kala-azar and cutaneous leishmaniasis within 6.5 months.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Control of schistosome-transmitting snails in Kenya by the North American crayfish Procambarus clarkii.
Snail-transmitted trematode parasites such as schistosomes and liver flukes assume considerable medical and veterinary significance in tropical Africa. We have observed a strong negative association between the presence of medically important pulmonate snails and the crayfish Procambarus clarkii in freshwater habitats in Kenya. This crayfish, introduced into Kenya around 1970, readily consumes these snails in the laboratory. Field enclosure experiments indicate that crayfish exert a significant negative impact on the abundance of Biomphalaria pfeifferi, the intermediate host of the human blood fluke Schistosoma mansoni. It is likely that P. clarkii will continue to spread naturally in Kenya and that schistosome-transmitting snails will be excluded or reduced in numbers where crayfish are present. Procambarus clarkii may represent an alternative, biological means of snail control in East Africa.
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Sensitivity of falciparum malaria to chloroquine and amodiaquine in four districts of western Kenya (1985-1987).
In-vivo and in-vitro studies to determine the sensitivity of Plasmodium falciparum malaria to chloroquine and amodiaquine were conducted in 4 districts of Western Kenya over a 2-year-period. Patients aged 5-60 years, were treated with chloroquine or amodiaquine base 25 mg/kg over 3 days. Recurrence of parasitaemia within 7 days (R1 resistance) or failure to clear parasites (R11 resistance) was observed in 27% of infections in West Pokot district, 51% in Busia, 45% in Bungoma and 19% in Rusinga Island. R111 resistance (failure to decrease parasitaemia by at least 75%) was documented in Rusinga Island. The proportions of parasites with minimum inhibitory concentrations (MICs) for chloroquine greater than 114 nM in in-vitro tests ranged from 37% in Busia to 68% in Bungoma. For amodiaquine, 20% of 30 isolates tested had MICs greater than 80 nM. We conclude that resistance to chloroquine is now established in the area and amodiaquine may be useful in uncomplicated chloroquine resistant falciparum infections in the region.
Adolescent↗
Malaria sporozoite detection by dissection and ELISA to assess infectivity of afrotropical Anopheles (Diptera: Culicidae).
Malaria infection rates determined by dissection and Plasmodium falciparum enzyme-linked immunosorbent assay (ELISA) were compared for 26,935 Anopheles gambiae Giles sensu lato and 17,739 Anopheles funestus Giles collected during 20 mo in western Kenya. ELISA infection rates were about 43% higher than dissection sporozoite rates. In dissection-negative Anopheles, circumsporozoite (CS) protein was detected by ELISA in 5.2% of 10,017 salivary gland samples and in 12.2% of 237 thorax samples. The accuracy of dissection and ELISA techniques was compared by the following tests on a group of 352 field-collected Anopheles (held 10 d to ensure sporogonic development): salivary gland dissection, examination of Giemsa-stained dissection slides, ELISA tests on salivary gland and thorax body parts, and microscopic techniques for determining sporozoite loads. Respective infection rates were 9.9%, 10.8%, and 15.6% for dissection, stained slides, and ELISA. Sporozoite loads were associated significantly with ELISA absorbance values (r = 0.76). Compared with Giemsa-stained dissection slide results, the sensitivity of sporozoite detection was 92.1% for dissection compared with 78.9% for ELISA; specificity was 100.0% for dissection versus 92.0% for ELISA. Immunological detection of CS protein in head-thorax samples of Afrotropical vectors overestimated the proportion of infective Anopheles because the comparison of techniques indicated that 45.4% of the ELISA positive Anopheles did not contain salivary gland sporozoites.
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