Characterisation of Leishmania isolates from Laikipia District, Kenya.

Using cloned kDNA sequences from the reference strain of Leishmania tropica IC-067, we have screened leishmanial isolates from Laikipia District of Kenya and identified these isolates as L. tropica. One isolate, IC-331, from a rat (Rattus rattus) was typed as L. tropica. This is the first time that L. tropica has been isolated from a wild rodent in Kenya and thus the first indication that the disease caused by L. tropica might be a zoonosis. The leishmanial isolates, especially those of sandflies, display extensive heterogeneity, prompting a need for selecting local and/or regional reference strains to generate species-specific DNA probes for use in identifying field isolates.

Studies on the vectors of leishmaniasis in Kenya: phlebotomine sandflies of Sandai location, Baringo district.

Adults of phlebotomine sandflies were collected from natural and man-made habitats in Sandai area of Baringo district using sticky and CDC light traps. Three sandfly species belongings to the Phlebotomus genus and eight species belonging to the Sergentomyia genus were recorded in the area. These flies fall into "perennial" group as they appeared to breed throughout the year. During the dry season there was an increase of sandfly densities in animal burrows and termite mounds, the main sandfly breeding places. Tree holes and human habitations constituted the major sandfly resting places during the wet season. Sandflies of the Phlebotomus genus were more collected in termite mounds and inside houses using CDC light traps, whereas in animal burrows they were more collected by sticky traps than by CDC traps. Sandflies of the Sergentomyia genus were equally collected by sticky traps and CDC light traps. However, in animal burrows and in human habitations, sandflies were more collected by CDC light traps than by sticky traps. On statistical analysis, CDC light traps seemed to be effective inside houses and in animal burrows. In termite mounds both traps yielded uniform results.

Effects of permethrin-treated screens on phlebotomine sand flies, with reference to Phlebotomus martini (Diptera: Psychodidae).

Effects of permethrin-treated screens on the sand fly, Phlebotomus martini Parrot, a vector of visceral leishmaniasis in Kenya, were evaluated after the eighth treatment. Screens treated with 0.50 g/m2 of permethrin 20% emulsifiable concentrate were fitted inside houses and re-treated every 6 mo from August 1989 to December 1993. Before application of the treated screens, a geometric mean of 0.83 P. martini were collected per trap night inside houses, whereas after the eighth treatment only 0.05 sand flies were caught. P. martini abundance was reduced by 88.8%. Analysis of the effects of treated screens on the total sand fly population (all species) indicated that 1.79 sand flies were collected per night per house before deployment of treated screens, whereas 0.16 flies were caught after the eighth treatment. The percentage of sand fly reduction inside treated houses increased with successive treatment of the screens, and a reduction of 81.4% was observed after the eighth treatment. Permethrin-treated screens did not reduce the sand fly engorgement rate inside houses.

Choice of resting sites by Anopheles gambiae (Diptera: Culici) in Mwea Rice Irrigation Scheme, Kirinyaga District, Kenya.

Investigations on Anopheles gambiae were carried out in Mwea Rice Irrigation Scheme, Kenya, to determine their preference for resting on various colours of fabrics and bare walls inside rural houses. The inside wall surface of each house was divided into upper, middle and lower sections and the section further partitioned into subsections measuring 0.6 x 0.3m. Two sets of experiments were conducted: one in which the walls were partly fitted with one colour of fabric at a time (double-choice situation), while in the other the walls were fitted with a combination of six colours (red, black, yellow, white, green and blue) of fabric at once, (multiple-choice situation). The number of mosquitoes resting on each of the pieces of cloth pinned to the walls and the uncovered subsections of the wall were recorded for each section of the wall after 24 hours. The results showed resting preference for cloth covered parts of the walls. The white colour was found to best attract mosquitoes followed by colours red, yellow, black, blue and green. The hanging strips in the middle of the houses had fewer mosquitoes resting on them than those on the wall.

Ecology of Sergentomyia garnhami, (Diptera:Psychodidae) in a kala-azar endemic area of Tseikuru, Kitui District, Kenya. I: The breeding sites.

The breeding sites of S. garnhami and other phlebotomine sandflies were investigated from February 1989-June 1990. Sandflies were recovered from 15 out of the 17 ecological habitats studied while S. garnhami was recovered from fourteen. Termite hills were the most preferred breeding sites for most phlebotomine sandflies but it was not possible to identify the preferred breeding sites of S. garnhami as all the sites yielded only one to three flies. S. garnhami were recovered from soil samples from both inside and outside human homes as well as from sylvatic sites. Daily pattern of emergence of sandflies showed that 60 days were sufficient for most sandflies to emerge while at least 100 days were required for S. garnhami.

Ecology of Sergentomyia garnhami, (Diptera:Psychodidae) in a kala-azar endemic area of Tseikuru, Kitui District, Kenya. II: Day resting sites.

A search for the day resting sites of S. garnhami and other phlebotomine sandflies in ten ecological habitats in Tseikuru area of Kitui District, Kenya, was carried out between November and December 1990. S. garnhami was collected in nine out of ten sites investigated, suggesting a wide distribution of the resting sites. S. garnhami constituted 23.4% of the total collections with termite hills being the most preferred site. Weekly trapping records showed that S. garnhami appeared in the field three weeks after the first rains of the season.

Host blood meals and chromosomal inversion polymorphism in Anopheles arabiensis in the Baringo District of Kenya.

Studies were carried out in the villages of Kapkuikui and Maji-Ndege in the Loboi area of Baringo District, Kenya, to obtain baseline data on species identification of the Anopheles gambiae group, their feeding and resting behavior, and their frequencies of chromosomal inversions. This was carried out towards predicting the effect of introducing permethrin-impregnated cloths or other intervention measures. In this study, Anopheles arabiensis was identified as the only species of the An. gambiae group. This species contained 2 inversions, 2Rb and 3Ra, occurring at frequencies ranging from 55 to 60%, and from 5 to 11%, respectively. There was no evidence for nonrandom mating. Indoor- and outdoor-collected samples were significantly different in respect of inversion 3Ra in one village and in the distribution of the different sources of blood meals in both areas. In these villages, 37% of indoor-resting mosquitoes fed outside before entering houses to rest.

Cutaneous leishmaniasis in Kenya: Sergentomyia garnhami (Diptera Psychodidae), a possible vector of Leishmania major in Kitui District: a new focus of the disease.

Investigations on phlebotomine sandflies in Tseikuru, Kitui District, Kenya were carried out to determine the vectors of Leishmania major. Sandflies were trapped from animal burrows over a period of one year using castor oil-smeared sticky traps. Nineteen phlebotomine sandfly species were identified and their prevalence in this habitat determined. Dissections on the parous sandflies resulted in the isolation of Leishmania parasites from Phlebotomus martini and Sergentomyia garnhami. The isolated parasites were cultured in NNN medium and were consequently mass cultured in RPMI medium for biochemical characterisation. The parasites from S. garnhami were typed as Leishmania major.

Malaria prevalence and morbidity in relation to the use of permethrin-treated wall cloths in Kenya.

The effect of permethrin-treated wall cloths (Mbu cloth) on malaria parasitaemia prevalences and malaria morbidity, was evaluated in a population of over 10,000 for a period of three years in the Marigat area, Baringo District, Kenya. The use of the treated cloth in 2,000 houses resulted in significantly lower rates of malaria parasite prevalences with an overall reduction rate of 73% (P < 0.001) in the treated area. Control areas had an initial increase in rate of malaria parasite prevalence of 30% and later a reduction of 31%. There was a slight reduction in spleen rates in the control and treated areas but it was not significant for either between the surveys or among the villages.

PIP: The use of pyrethroid-treated fabrics against disease vectors is a well-accepted vector control strategy worldwide. Most studies have assessed the merits of using impregnated bednets, but this prevention strategy is inappropriate for many households in many communities due to incompatible cultural norms, high cost, the lack of conventional western style beds, sleeping arrangements which differ between cultures, and differences between housing construction styles in rural communities. The International Center of Insect Physiology and Ecology recently developed a technology using cotton wall cloth, Mbu cloth, to control vectors of malaria and leishmaniasis in rural communities in Kenya. Other fabrics such as polyester have even improved the technology by making the cloth lighter and cheaper. The authors evaluated the effect of permethrin-treated Mbu cloth on malaria parasitemia prevalences and malaria morbidity in a population of over 10,000 for a period of 3 years in the Marigat area of Baringo District, Kenya. 2000 houses were fitted with the cloth. The prevalence of malaria parasites was reduced an overall 73% in the treated area. Control areas saw a 30% initial increase in the rate of malaria parasite prevalence followed by a reduction of 31%. Slight reductions in spleen rates were also observed in the control and treated areas, but were insignificant between the surveys and among the villages.

Defecation by Anopheles arabiensis mosquitoes of host blood infected with live Trypanosoma congolense.

Female Anopheles arabiensis mosquitoes were experimentally fed on hamsters and BALB/c mice which were either clean or infected with Trypanosoma congolense. The mosquitoes readily fed on either animal. A blood repletion rate of 82.7% was recorded for mosquitoes feeding on hamsters. Seventy seven per cent of the replete mosquitoes continued to feed while at the same time defecating the host's blood in droplets, ejected in quick succession from the anus. Ninety five per cent of mosquitoes defecating blood while feeding on mice infected with T. congolense ejected live parasites along with the blood. Clean mice inoculated intraperitoneally with T. congolense via tail or defecated blood developed parasitaemia between the third and seventh day. This phenomenon could imply possible mechanical transmission of the parasites to the hosts being fed on by the mosquitoes.

Effect of rice husbandry on mosquito breeding at Mwea Rice Irrigation Scheme with reference to biocontrol strategies.

A study was carried out at Mwea Rice Irrigation Scheme, Kenya, to assess the impact of rice husbandry on mosquito breeding and identify indigenous biocontrol agents with potential for controlling mosquito breeding in the scheme. The study established a close relationship between the schedule of the farming practices (particularly the flooding phase) and mosquito breeding. Two groups of agents, entomopathogenic bacteria (Bacillus thuringiensis var. israelensis) and larvivorous fish, were identified. Laboratory evaluation of the agents produced encouraging results. The bacterial isolates showed broad-spectrum larvicidal potency against Anopheles, Culex and Aedes mosquito larvae and 2 of the fish species, Tilapia zilli and Oreochromis niloticus, demonstrated a strong predation for a mosquito larval diet. To facilitate their use in effective biocontrol strategies, the agents would require further evaluation under field conditions.

A bioassay to evaluate the efficacy of permethrin-impregnated screens used against phlebotomine sandflies (Diptera: Psychodidae) in Baringo District of Kenya.

Control of phlebotomine sandflies remains a difficult problem throughout the world because of the insects' very highly specialized breeding sites. Use of insecticides remains one effective methods for managing sandflies. The present studies were conducted to establish how long permethrin impregnated wall cloth remains effective against sandflies. Cotton cloth, impregnated with permethrin (0.5g/m2) were hung inside experimental houses in Baringo District, Kenya, for the control of sandflies. Small pieces of cloth were cut off from the screen every month for 12 months, and bioassayed against sandflies. The cloth was found to remain effective against sandflies for 6 months.

Evaluation of the residual efficacy of permethrin-impregnated screens used against mosquitoes in Marigat, Baringo district, Kenya.

Insecticide-impregnated screens and bednets are gradually finding wider use in malaria control programmes. The efficacy of these devices is dependent on the method of application, the acceptability by the people and effectiveness of the insecticide used. The present studies were carried out to determine the duration of the effectiveness of a permethrin-impregnated wall cloth (Mbu cloth) used in the Marigat area of Baringo District, Kenya in order to ensure its effective use. Cotton cloth impregnated with permethrin was hung inside an experimental house in Marigat and small pieces cut off each month for bioassay against mosquitoes over a twelve month period. The wall cloth remained effective for 6, 4 and 10 months against Anopheles gambiae s.l. the known vector of malaria, Culex quinque-fasciatus and Aedes aegypti, respectively.

Differentiation of vector species of phlebotominae (Diptera: Psychodidae) in Kenya by chorionic sculpturing of their eggs.

Chorionic sculpturing on eggs of Phlebotomus pedifer Lewis, Mutinga, and Ashford; the closely related Phlebotomus aculeatus Lewis, Minter, and Ashford (= P. elegonensis Ngoka, Madel, and Mutinga); and Phlebotomus martini Parrot was examined and compared by scanning electron microscopy. The eggs of P. pedifer had a general pattern of longitudinal ridges; those of P. aculeatus and P. martini exhibited intraspecific differences. Chorionic patterns of eggs were not reliable to differentiate these species. It is suggested that other methods of differentiation should be used on these species.

Recombinant kinetoplast DNA (kDNA) probe for identifying Leishmania tropica.

The paper reports on the construction of a kDNA library with DNA isolated from the WHO reference strain of Leishmania tropica IC-305 and subsequent identification and propagation of recombinant plasmids containing L. tropica kDNA sequences. It also shows that the cloned kDNA sequences can be used as genetic markers in restriction endonuclease, Southern blot transfer, and dot blot hybridisation analysis, to identify L. tropica parasites. When the pL 305-I kDNA probe was used in hybridisation experiments with DNAs from various Leishmania reference strains, species and isolates from different host species and from different geographical locations, hybridisation was detected only with L. tropica, thereby suggesting that the insert in recombinant plasmid 305-I was species-specific. The probe is sensitive to the level of 10(3) parasites in dot blot hybridisation. Additionally, orthogonal field alternation gel electrophoresis (OFAGE) and transverse alternating field electrophoresis (TAFE) were used to characterise Leishmania reference strains and Leishmania species. The molecular karyotypes resolved by these techniques showed significant differences in the profiles of chromosomal sized-DNA molecules among species of Leishmania. The DNA karyotypes of the two reference strains of L. tropica (IC-305 and NLB-067), while similar, were nevertheless distinct.

Isolation of mosquito-toxic bacteria from mosquito-breeding sites in Kenya.

A large number of source materials were collected for isolating entomopathogenic bacteria from larval mosquito habitats in Kirinyaga District, Kenya. Mosquito-toxic bacteria were included among the numerous types of microorganisms isolated from the habitats. The pathogenic isolates shared common structural characteristics; they were gram-positive, spore-forming bacilli that produced parasporal inclusions conferring broad-spectrum larvicidal activity against Anopheles, Culex and Aedes mosquitoes. Based on structural and growth characteristics, coupled with larvicidal activity, the pathogenic isolates were tentatively identified as variants of Bacillus thuringiensis. Although the collection consisted of a variety of items including soil, silt and mud, the most productive materials were larval bodies. Using healthy mosquito larvae held in a fully permeable plastic bottle, a baiting technique was developed as a means of recovering bacteria from the environment.

Visceral leishmaniasis and malaria prevalence in West Pokot District, Kenya.

The prevalence of visceral leishmaniasis and malaria in the human population of West Pokot district of Kenya was studied in 1986. A total of 2139 people was proportionately screened for the two diseases according to four age categories (0-4, 5-14, 15-44 and greater than 45 years). Diagnostic methods included the enzyme linked immunosorbent assay (ELISA) and Leishmanin skin test for visceral leishmaniasis, and parasitological examination for malaria. The epidemiological value of the spleen rate was evaluated in relation to visceral leishmaniasis and malaria endemicity. A general decline of infection rates with altitude was observed for both diseases. Visceral leishmaniasis was less prevalent than malaria, with less than 2% active cases in any age group and had the same distribution in both sexes. Malaria infection rate was highest in the younger age groups, declining from 21.5% in the 0-4 year old age group to 5.5% in people more than 45 years old. Malaria affected significantly more males than females. The spleen rate was inappropriate for epidemiological survey of either malaria or visceral leishmaniasis due to an overlap in the distribution of the two diseases.