Search PubMed⌕ Search

Biomedical subjects

D K Koech

Publications and source records attributed to D K Koech.

At least 55 records · Page 3Linked to original sources
PubMed1990

Differentiation of Anopheles gambiae and An. arabiensis (Diptera: Culicidae) by ELISA using immunoaffinity-purified antibodies to vitellogenin.

Yolk proteins (vitellogenin and vitellin) proved to be excellent marker molecules for separating Anopheles gambiae Giles and An. arabiensis Patton, two morphologically indistinguishable members of the An. gambiae species complex. A rabbit polyclonal antibody directed against An. gambiae yolk proteins was made species-specific by removing immunoglobulins that crossreacted with An. arabiensis by immunoaffinity chromatography. The resultant antibody was 400 times more sensitive to An. gambiae and was employed as the secondary antibody in a modified double antibody "sandwich" ELISA, which also used monoclonal antibodies to anopheline vitellogenin as the primary or coating antibody. This ELISA easily differentiated soluble yolk protein samples from An. gambiae and An. arabiensis. A field study with 628 females of An. gambiae complex collected in western Kenya demonstrated that the ELISA results were 98.4% in agreement with the standard cytotaxonomic method.

Animals↗
PubMed1990

Characterization of malaria transmission by Anopheles (Diptera: Culicidae) in western Kenya in preparation for malaria vaccine trials.

Malaria transmission was studied for 33 mo in the villages of Kisian and Saradidi in western Kenya in preparation for field trials of malaria vaccines. Abundance estimates of Anopheles gambiae Giles sensu lato and Anopheles funestus Giles, which constituted over 99% of 26,645 anophelines collected, were compared for all-night biting collections inside houses, outdoors, and in tents. The overall numbers of Anopheles per man-night were 2.3 times greater in Kisian than in Saradidi. For the three types of collections, mean sporozoite rates by dissection ranged from 2.2 to 5.4% for 13,072 Anopheles in Kisian and from 9.9 to 13.6% for 7,058 Anopheles in Saradidi; greater than 90% of the infections were Plasmodium falciparum, either alone or mixed with P. malariae or P. ovale. Heaviest transmission from April to July coincided with the end of the long rainy season. Entomological inoculation rates (EIR) averaged 0.82 infective bites per man per night inside houses in Kisian and 0.65 in Saradidi. Outdoors, EIRs averaged 0.09 in Kisian and 0.52 in Saradidi. In tents, which were evaluated to identify methods for exposing nonindigenous volunteers during vaccine efficacy trials, EIRs were 3.3 and 2.5 times less than inside houses for Kisian (EIR = 0.25) and Saradidi (EIR = 0.26), respectively. Exposure in tents averaged one infective bite every 4.0 d in Kisian and every 3.8 d in Saradidi. The use of tents in vaccine efficacy trials should provide adequate exposure for nonindigenous volunteers. Malaria vaccine trials could be conducted efficiently in western Kenya, with timing dependent upon the intensity of transmission required by vaccine trial objectives.

Analysis of Variance↗
PubMed1990

Development of Leishmania major in Phlebotomus duboscqi and Sergentomyia schwetzi (Diptera: Psychodidae).

The extrinsic development of Leishmania major was observed in 2 man-biting sand flies, Phlebotomus duboscqi, a known vector, and Sergentomyia schwetzi, an assumed non-vector. Flies fed on a leishmanial lesion on the nose of a hamster were examined for infection at 0, 6, 12, 18, 24, 36, 48, and 60 hr and at approximately 24 hr intervals from day 3 to day 14 post-feeding. Infection rates, determined by light microscopy, were 47% (n = 258) in P. duboscqi and 5% (n = 162) in S. schwetzi. Transformation from amastigotes to "procyclic" promastigotes occurred in both species at 6-18 hr post-feeding. In P. duboscqi, the parasites multiplied rapidly and developed through as many as 10 forms, including at least 3 dividing-promastigote forms. Metacyclic promastigotes, the "infective" form, appeared at 6 days post-feeding, first in the region of the stomodeal valve, then in the pharynx, cibarium, and proboscis. In a single attempt 14 days post-feeding, a P. duboscqi transmitted L. major to a mouse by bite. In contrast, the parasites multiplied slowly in S. schwetzi, and did not develop beyond "procyclic" promastigotes. The parasites did not migrate anteriorly nor survive beyond 90 hr post-feeding, indicating that S. schwetzi is not a vector of L. major. Classical strategies for vector incrimination may be confounded by the isolation of non-infective early developmental forms of Leishmania from wild-caught non-vectors.

Animals↗
PubMed1990

Low dose oral alpha-interferon therapy for patients seropositive for human immunodeficiency virus type-1 (HIV-1).

Thirty eight symptomatic and two asymptomatic patients seropositive for human immunodeficiency virus type-1 (HIV-1) were treated with a natural human interferon alpha (HuIFN alpha). Patients were given 2 IU/kg HuIFN alpha orally once daily in powdered maltose held in the mouth to promote mucosal absorption. This oral immunomodulating HuIFN alpha therapy resulted in an increase in CD4+ lymphocytes, an increase in weight, and a dramatic alleviation of clinical symptoms related to HIV-1 infection.

Administration, Oral↗
PubMed1990

Relative abundance and blood feeding behavior of nocturnally active culicine mosquitoes in western Kenya.

At 2 sites in western Kenya targeted for future malaria vaccine trials, adult culicine mosquitoes were sampled over one year by 5 collection techniques to assess human exposure to potential vectors of pathogens other than malaria. Collections included 20,910 females representing 19 species in Kisian and 4,312 females of 11 species in Saradidi. Common species in Kisian included Culex quinquefasciatus (71.4%), Mansonia uniformis (15.8%), Ma. africana (6.2%), Aedes mcintoshi (2.0%), Coquillettidia fuscopennata (1.9%) and Ae. ochraceus (1.8%). Common species in Saradidi included Cx. quinquefasciatus (92.7%), Cx. nebulosus (4.5%) and Ma. uniformis (1.0%). Human-bait collections identified 16 man-biting culicine species in Kisian and 9 in Saradidi. Man-biting rates at Kisian for the 5 most common species were 1.8, 14.6 and 13.5 times higher than at Saradidi for indoor, outdoor and tent collections, respectively. Exposure indoors was estimated to be 1,277 bites/man/year at Kisian and 720 at Saradidi. Blood meal identification for 1,083 mosquitoes confirmed that the common culicine species feed primarily on humans and cows.

Animals↗
PubMed1990

Outcome of intervention with or without low dose oral interferon alpha in thirty-two HIV-1 seropositive patients in a referral hospital.

Thirty two critically ill patients were admitted to Kenyatta National Hospital with a diagnosis of HIV-1 seropositivity on both ELISA and Western Blot between October 1989 and January 1990. Sixteen of the patients received low dose oral interferon alpha while the other 16 patients received intensive supportive management alone. Of the 16 patients who received low dose interferon alpha, 14 were discharged from the Hospital within 2 to 4 weeks of admission in a reasonable state of health while two of the patients died after 18 and 42 days from the time of admission. All the 16 patients who received intensive supportive management alone were dead within 4 weeks of entering the Hospital, their mean (+/- SD) stay after admission being 8.6 +/- 6.8 days. These results suggest that low dose oral interferon alpha may be of value in the care of critically ill HIV-1 seropositive patients.

Adolescent↗
PubMed1990

Efficacy of Kemron (low dose oral natural human interferon alpha) in the management of HIV-1 infection and acquired immune deficiency syndrome (AIDS).

One hundred and ninety nine symptomatic and 5 asymptomatic patients seropositive for the human immunodeficiency virus type 1 (HIV-1) were treated with KEMRON, a natural human interferon alpha (nHIF alpha) stabilized in a complex polysacchariche carrier. Treatment was given for at least 10 weeks at a daily oral dose of approximately 2.0 IU of nHIF alpha per kg body weight. Karnofsky performance score increased from an average of 60.5 on entry into the study to 100 by the 10th week after treatment. Similarly, common clinical complaints associated with HIV-1 infection rapidly reduced per patient from an average of 3.8 to 0.05 and 0 by week 8 and 10 of treatment. Eighteen of the patients serodeconverted by both ELISA and western blot assays during the study period. These observations suggest that KEMRON used as recommended is beneficial in HIV-1 seropositive individuals.

Adolescent↗
PubMed1990

Treatment of HIV infections and AIDS: new horizons.

Treatment of HIV infections has involved the use of antiviral drugs as well as those drugs that act against opportunistic infections. Immune modulators have also been used. A review of these drugs is reported emphasizing on those which have great promise in the clinical management of HIV infections in the light of our present knowledge on immunopathology of the disease.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Anopheles gambiae complex egg-stage survival in dry soil from larval development sites in western Kenya.

The potential for Anopheles egg survival in dry soil from larval development sites was investigated in western Kenya. A total of 230 dry soil samples collected in 1987, 1988 and 1989 yielded 126 first-instar Anopheles gambiae s.l. larvae from 2 to 5 days after flooding with water. These larvae were from dried animal hoofprints along streams (57.9%), from dried edges of permanent and temporary pools (41.3%) and from dried stream beds (0.8%). Larval density was 1.2 larvae/kg of soil from positive microhabitats in 1987 and 2.4 larvae/kg in 1988. Thirteen larvae from the 1989 soil samples, reared to adults, were identified by DNA probes as Anopheles gambiae sensu strictu (n = 6) and Anopheles arabiensis (n = 7). Experimentally, eggs from field-collected females remained viable up to 12 days for An. gambiae s.l. and 10 days for An. funestus. In western Kenya, egg viability in dry soil may represent a significant, short-term survival mechanism for 2 species of the An. gambiae complex.

Animals↗
PubMed1989

Plasmodium falciparum: DNA probe diagnosis of malaria in Kenya.

We previously reported isolation of DNA probe which specifically recognizes Plasmodium falciparum and developed a simple method for its use. The sensitivity and specificity of this DNA probe method have now been extensively field tested in comparison with those of conventional microscopic examination of blood films in two separate studies in Malindi, Kenya, involving a total of 1179 patients. In the second study, which used improved techniques, sensitivity of the DNA probe was 89% when compared to microscopy. We conclude that the DNA probe method compares favorably with conventional microscopy in detecting parasite densities as low as 25 parasites per microliter of blood. A significant advantage of the DNA probe method is that it utilizes a standardized procedure which can simultaneously and reproducibly analyze a large number of samples without opportunity for significant reader bias.

Adult↗
PubMed1989

Effect of human circumsporozoite antibodies in Plasmodium-infected Anopheles (Diptera: Culicidae).

Human circumsporozoite (CS) antibodies to Plasmodium falciparum were detected in blood meals from 45.0% of 1,547 field-collected Anopheles gambiae Giles sensu lato and Anopheles funestus Giles from western Kenya. Possible effects on malaria infections within the Anopheles host were investigated. Circumsporozoite antibodies were detected in blood meals up to 36 h after feeding. Antibodies crossing the midgut were detected experimentally in hemolymph from 4 to 36 h after feeding; human IgG also was present in hemolymph from fully gravid field-collected Anopheles. Ingestion of high-titer human CS antibodies or 2A10 monoclonal antibody to P. falciparum sporozoites by P. falciparum-infected An. gambiae, 10 d after feeding on an infected human, had no effect on oöcyst maturation, sporozoite rates, or sporozoite loads. Contact between CS antibodies and sporozoites in the hemocoel did not block sporozoite invasion of salivary glands. Human IgG antibodies were detected by an indirect fluorescent antibody technique on salivary gland sporozoites from 83.3% of 114 field-collected Anopheles. In 65.4% of 26 infections, antibodies persisted on sporozoites for at least three days. Thus, a high proportion of naturally infected An. gambiae s.l. and An. funestus in western Kenya transmit sporozoites that are bound with human IgG acquired during previous blood meals. The infectivity of such sporozoites needs to be determined in relation to natural transmission and to the potential use of malaria sporozoite vaccines.

Animals↗
PubMed1989

Inter-subject variability in the metabolism of proguanil to the active metabolite cycloguanil in man.

1. The metabolism of proguanil to the active metabolite cycloguanil has been evaluated in 135 British Troops and 26 Kenyan schoolchildren. 2. Large inter-subject variability was observed in both plasma and urinary concentrations of proguanil and cycloguanil after standard doses of drug. 3. Based on the ratio of proguanil to cycloguanil (P/C) in urine the British troops formed a non-normal distribution. 90% of the population formed a discrete distribution with P/C ranging from 0.5 to 9.0 while the remaining 10% were scattered throughout the distribution to an extreme value of 39. A similar pattern of variability was observed using P/C from a 6 h plasma sample. 4. This variability was due to differences in the ability of individuals to metabolise proguanil to cycloguanil. 5. Thirteen schoolchildren who had experienced malaria during prophylaxis with proguanil and thirteen matched controls each received proguanil (100 mg). We could not discriminate between the two groups based on P/C ratio in either a 6 h plasma or 0-6 h urine sample.

Adolescent↗
PubMed1989

Identification of snails infected with schistosomes by ELISA employing monoclonal antibodies: Schistosoma mansoni in laboratory snails (Biomphalaria glabrata) and in field snails (Biomphalaria pfeifferi) from Kenya.

An enzyme-linked immunosorbent assay (ELISA) employing monoclonal antibodies was used for detecting Schistosoma mansoni antigens in hemolymph of laboratory snails (Biomphalaria glabrata) in Kenya. Infected laboratory snails shedding cercariae were differentially identified by ELISA from uninfected snails with 100% sensitivity and specificity. Prepatent infections were detected by ELISA from 2 weeks after exposure to miracidia. Thus, ELISA revealed infection 3 weeks before maximal patency was reached (5-6 weeks post-exposure). Infected field snails (B. pfeifferi) shedding cercariae were differentially identified by ELISA, with 100% sensitivity and specificity, from uninfected field snails and from snails naturally infected with other trematodes (echinostomes and strigeids). Prepatent infections with S. mansoni were readily identified by ELISA in field snails. A case is demonstrated where infection rate, as determined by shedding test alone, was 9.8%, whereas the combined figure of prepatent and patent infection rates was 22.9%

Animals↗
PubMed1988

Efficacy of multiple-dose halofantrine in treatment of chloroquine-resistant falciparum malaria in children in Kenya.

Halofantrine hydrochloride given to 46 Kenyan children with falciparum malaria at 10 mg/kg for two doses, and to 60 other children at 8 mg/kg for three doses, resulted in rapid parasite clearance, mean parasite clearance times being 45.4 h and 54.8 h, respectively. In-vitro chemosensitivity tests showed that most infections were due to chloroquine-resistant parasites, and that parasite maturation was inhibited by considerably lower concentrations of halofantrine than of chloroquine.

Administration, Oral↗
PubMed1988

Chlorproguanil/dapsone for the treatment of non-severe Plasmodium falciparum malaria in Kenya: a pilot study.

Chlorocycloguanil, the active metabolite of chlorproguanil, was synergistic in vitro with dapsone against 2 culture-adapted Plasmodium falciparum isolates from Kenya; maximal synergy occurred at lower concentrations that it did with pyrimethamine and sulfadoxine. 48 children with asymptomatic P. falciparum infections were treated with chlorproguanil (at a target dose of 1.2 mg/kg) and dapsone (target dose of 1.2 or 2.4 mg/kg); all were free of parasitaemia by day 7. The following numbers had recurrences on days 14, 21, and 28, respectively: 1 of 48, 7 of 47, and 7 of 40. All 39 children treated with pyrimethamine (target dose 1.2 mg/kg) and sulfadoxine (target dose 24 mg/kg) were cleared of infection, while the following had recurrences on days 14, 21, and 28: 1 of 39, 2 of 38, and 2 of 36. The rate of decrease in parasitaemia was the same in the 2 groups, and there was no change in haematocrit or haemoglobin during the follow-up. The rate of recurrence in the children receiving chlorporguanil/dapsone was higher, probably because these drugs have a much shorter clearance time than pyrimethamine/sulfadoxine. Chlorproguanil/dapsone is an effective combination for treating P. falciparum malaria and deserves further study.

Animals↗
PubMed1987

Inadequacy of chlorproguanil 20 mg per week as chemoprophylaxis for falciparum malaria in Kenya.

After treatment with chloroquine and pyrimethamine/sulfadoxine, 118 school children aged 6 to 10 years living near the Kenyan coast were enrolled in a malaria chemoprophylaxis study and followed up for 20 weeks. Children were randomly assigned to receive either chlorproguanil 20 mg weekly (n = 78) or placebo (n = 37). The attack rate of Plasmodium falciparum infection was 42% in chlorproguanil recipients (39.8 episodes per 1000 person-weeks of prophylaxis) and 73% in placebo recipients (69.2 episodes per 1000 person-weeks, p less than 0.02). Sensitivity tests on 36 isolates successfully cultured in vitro showed that all 21 isolates from chloroproguanil recipients were resistant to dihydrofolate-reductase inhibitors, whereas only 3 of 15 isolates from the placebo group were resistant (p less than 10(-6)). Chlorproguanil in a weekly adult dose of 40 mg does not provide adequate prophylaxis against P falciparum in Kenya, probably because drug levels between doses fall below those required to suppress parasites resistant to dihydrofolate-reductase inhibitors.

Adolescent↗