African programme for Onchoceriasis control: ophthalmological findings in Bushenyi, Uganda.

BACKGROUND: The overall prevalence of blindness from Onchoceriasis in Bushenyi is relatively low, most of which is to be found in the elderly. Onchoceriasis is a major health problem in Africa. The Community-Directed treatment with invermectin is a control strategy to address the problem, but baseline data are generally lacking in several countries. OBJECTIVE: To describe baseline ophthalmological data in order to assess the impact of Community-Directed with Ivermectin (CDTI) in Uganda. METHODS: The study site was in Bushenyi, Western Uganda. In a cross-sectional study, 367 persons aged 10 years or older from seven selected villages received eye examination using a standardised protocol and Wu-Jones Motion Sensitivity Testing (MSST). Besides MSST, other information sought included visual acuity, slit lamp examination, testicular opacities and intraocular presence. RESULTS: Of the 367 subjects, 219(57.2%) were males. Subjects less than 25 years of age were 104(28.3). The prevalence of blindness were 1.9% while 4.1% was visually impaired by acuity criteria alone. A further 9.1% had moderate visual field loss while 2.8% had severe field loss. There was no case of anterior chamber microfilaria but dead microfilariae were seen in two cases. Punctate keratitis was present in 1.8% with sclerosing keratitis was twice as common at 3.8%. Optic atrophy was also relatively common at 12.4%, while chorioretinitis was present in 3.3%. CONCLUSION: There was an apparent paucity of acute onchocerciasis-related lesions but a significant presence of irreversible onchocerciasis-related lesions. The most significant problem requiring intervention would appear to be cataract.

Investigations into the isolation of the Tukuyu focus of onchocerciasis (Tanzania) from S. damnosum s.l. vector re-invasion.

As part of the feasibility study for an onchocerciasis vector elimination project we investigated the isolation of the Tukuyu focus in Tanzania from possible vector re-invasion. This was achieved by examining the distribution of the Simulium damnosum complex vector cytospecies outside the focus to look for potential sources of re-invasion. Besides cytotaxonomic identifications of the aquatic stages, we applied morphotaxonomic and molecular techniques to identify S. thyolense and confirm it as the anthropophilic species in both the Tukuyu and the neighbouring Ruvuma foci. We detected significant differences in chromosome inversion frequencies between the Tukuyu populations and those breeding to the southwest in the adjacent Songwe river basin and in northern Malawi (where there is no man-biting and no onchocerciasis), suggesting that there is not normally a great deal of migration in either direction. By contrast, populations of S. thyolense from the Tukuyu and Ruvuma foci (150km southeast of Tukuyu) were much more similar in terms of their chromosomal polymorphisms, indicating a higher possibility of re-invasion, although migration is still restricted to some extent, as indicated by some differences in chromosome polymorphisms between the two foci. Future migratory events which might be associated with vector control operations can be monitored by vector cytospecies identification, the frequency of polymorphic inversions which characterise the different vector populations, and the identification of accompanying non-vector cytospecies (e.g. S. plumbeum and cytotype Kasyabone occur exclusively in the two foci, and hence their re-appearance in Tukuyu could have only one outside source). The morphology of the scutal pattern of neonate males may act as a quick test for vector species identification where chromosome squashes are unavailable.

APOC impact assessment studies: baseline ophthalmological findings in Morogoro, Tanzania.

The goal of the African Programme for Onchocerciasis Control (APOC) is to eliminate Onchocerciasis as a disease of public Health significance and an important constraint to socio-economic development in the 19 none OCP (Onchocerciasis Control Project) countries covered through Community-Directed Treatment with Ivermectin, CDTI. In 1998, impact assessment studies were carried out in Morogoro, Tanzania during which baseline ophthalmological parameters were established. The hypothesis being tested is that CDTI will prevent or delay progression of onchocercal eye lesions and blindness. A total of 425 subjects aged 10 years or more from 14 villages within Bwakira district ofMorogoro region in Tanzania were examined for Snellen visual acuity, ocular microfilaria, lens opacities, uveitis and posterior segment disease especially chorioretinitis and optic nerve disease. Motion Sensitivity Screening Test (MSST) was carried out as well. Microfilaria was present in the anterior chamber of nearly half (49.2%) of all subjects examined. Prevalence of blindness was extremely high at 15.2%. Onchocercal lesions were responsible for blindness in 41.5% of these, followed by cataracts (27.7%), glaucoma (10.8%) and trachoma (6.2%). The main pathway to onchocercal blindness in this population was anterior uveitis with or without secondary cataracts. There is an urgent need to get CDTI underway and institute other horizontal primary eye care measures, especially cataract backlog reduction, in order to reduce the excessive burden of avoidable blindness in this community.

Onchocerciasis situation in the Tukuyu focus of southwest Tanzania after ten years of ivermectin mass treatment.

A purposive cross-sectional epidemiological study was conducted in the Tukuyu Onchocerciasis focus in south-western Tanzania in 2004, ten years after launching the ivermectin mass treatment programme, and 23 years after establishing focal parasite prevalence. The objective was to assess contemporary Onchocerciasis clinical and parasitological situation and assess community knowledge about the disease and its control. From historical data, five villages with high parasite prevalence were selected, two each on the Lufilyo and Kiwira Rivers and one on lower Lumbira River. Skin biopsies were taken from the iliac crest on the left and right buttocks, for examination of Onchocerca volvulus microfilariae. Onchocercal skin lesions were checked using natural light, while nodules were palpated from head to ankles and scored. A structured questionnaire was administered to participants. A total of 438 persons (age=16-99 years) were examined. No skin microfilariae (mf) were detected. Onchocercal skin symptoms were found in 170 (38.8%), of which 30 (6.9%) had nodules, 48 (11.0%) chronic onchodermatitis and 92 (21%) itching. One-third (34.5%) had correct knowledge that black flies ("tusunya") are vectors of onchocerciasis. Half of the respondents (n=217) confirmed taking ivermectin for onchocerciasis treatment, and 428 (97.7%) were willing to continue for any duration. It is concluded that the undetectable skin microfilariae in the study sample was partly attributable to the consequences of ongoing ivermectin mass treatment. It is recommended that the control efforts, as well as monitoring and evaluation be sustained to determine its long term impact, and that a more sensitive technique be used to check O. volvulus skin mf prevalence.

Susceptibility of Simulium damnosum complex larvae to temephos in the Tukuyu onchocerciasis focus, southwest Tanzania.

Tukuyu onchocerciasis focus was earmarked for vector control using insecticide against larval stages. Susceptibility tests of mature larvae of Simulium damnosum s.l. vectors to temephos insecticide were carried out before and after two years of insecticide treatment of rivers within Tukuyu onchocerciasis focus, south-western Tanzania. The tests were done in 1999/2000 and 2004 using WHO standard methods. Mature larvae were exposed to 9 concentrations of temephos active ingredient, from the weakest 0.00975mg/litre to the strongest of 2.5mg/l. Each test concentration and control was run in duplicates of 25 larvae each, set for three hours in a cool temperature. After incubation, test solution was discarded and larval condition checked. Numbers of larvae in each category were recorded and used to determine mortality rate for each concentration as well as for the LC50 and LC95. A total of 1,666 larvae were tested, 942 during the pre- and 724 post-treatment. Results showed that both pre and post-treatment samples were susceptible, attaining 100% mortality at the diagnostic dose of 1.25mg/l, and LC50 between 0.129-0.34mg/l pre - and 0.144-0.211 mg/l (95% CI, P < 0.05) post- treatment. These values fall within the standard diagnostic dose of < or = 0.4mg/l for susceptible S. damnosum s.l populations. It was concluded that the endemic S. damnosum population was susceptible to temephos before and after two years of intermittent field application. Temephos was thus recommended for continued use in onchocerciasis vector control in the Tukuyu focus, to complement Community Directed Treatment with Ivermectin, but close monitoring of vector susceptibility should be done.

Susceptibility of Simulium damnosum complex larvae to temephos in the Tukuyu onchocerciasis focus; southwest Tanzania

Tukuyu onchocerciasis focus was earmarked for vector control using insecticide against larval stages.Susceptibility tests of mature larvae of Simulium damnosum s.l. vectors to temephos insecticide were carried out before and after two years of insecticide treatment of rivers within Tukuyu onchocerciasis focus, south-western Tanzania. The tests were done in 1999/2000 and 2004 using WHO standard methods. Mature larvae were exposed to 9 concentrations of temephos active ingredient, from the weakest 0.00975mg/litre to the strongest of 2.5mg/l. Each test concentration and control was run in duplicates of 25 larvae each, set for three hours in a cool temperature. After incubation, test solution was discarded and larval condition checked. Numbers of larvae in each category were recorded and used to determine mortality rate for each concentration as well as for the LC50 and LC95. A total of 1,666 larvae were tested, 942 during the pre- and 724 post-treatment. Results showed that both pre and post-treatment samples were susceptible, attaining 100% mortality at the diagnostic dose of 1.25mg/l, and LC50 between 0.129-0.34mg/l pre - and 0.144-0.211 mg/l (95% CI, P<0.05) post- treatment. These values fall within the standard diagnostic dose of ≤0.4mg/l for susceptible S. damnosum s.l populations. It was concluded that the endemic S. damnosum population was susceptible to temephos before and after two years of intermittent field application. Temephos was thus recommended for continued use in onchocerciasis vector control in the Tukuyu focus, to complement Community Directed Treatment with Ivermectin, but close monitoring of vector susceptibility should be done

Malaria in Bulambya, Ileje district, south-west Tanzania.

This study was carried out to determine malaria situation in Bulambya Division, Ileje district in southwest Tanzania. Outpatient attendance records from 1999 to 2002 were examined for malaria cases in eleven health facilities. A cross-sectional study to determine malaria prevalence and its potential vectors was done in May 2004. Blood samples were collected from 502 schoolchildren from 16 primary schools and examined microscopically for malaria parasites. Indoor resting mosquitoes were collected in ten houses in each of the ten villages covered. Health facility data for 1999 showed the highest (60.7%) and lowest (11.5%) annual malaria morbidity rates were recorded at Itumba and at Ibaba, respectively. Malaria parasitaemia rate among schoolchildren ranged from 0-36.7%; the lowest prevalence was observed in the high altitude mountainous range and the highest in the lower altitude plateaux. Of 1,504 mosquitoes caught, 205 (13.6%) were female Anopheles gambiae s.l., 215 (14.3%) An. funestus and 68.9% were culicines. Data from both health facility records and school surveys indicate that there is high malaria morbidity in the lower plateaux (1100 to =1350 m), around Itumba and Isongole, where indoor anopheles mosquito densities were relatively higher than in the higher altitudes (> 1,350 m) around Ibaba. In the lower altitude range, there was less malaria on steep slopes than on flat terrain. Further studies are recommended to closely monitor malaria situation in these epidemic prone highlands of southwest Tanzania.

Cytogenetic and PCR-based identification of S. damnosum "Nkusi J" as the anthropophilic blackfly in the Uluguru onchocerciasis focus in Tanzania.

A combined molecular and cytogenetic analysis was used to identify the local blackfly vectors of onchocerciasis in the Uluguru Mts. focus, Morogoro region, central Tanzania. Cytotaxonomic identification revealed the occurrence of three cytospecies of the Simulium damnosum complex, along altitudinal gradients. The cytoform "Nkusi" was found breeding at low to mid-altitudes (100-500 m), while S. kilibanum was found at mid- and high altitudes (300-1260 m), being sympatric with "Sebwe" only in the highlands. The analyses further revealed the cytoform "Nkusi" from the nearby Kilosa focus. Simulium kilibanum and "Nkusi" are potential vectors of onchocerciasis, while the "Sebwe" form is considered non-anthropophilic and therefore not a vector. By means of molecular typing of wild-caught females, "Nkusi" was incriminated as the man-biting fly at all catching sites, and consequently, is the assumed vector of onchocerciasis over the full altitude range. In the high altitude zones, however, S. neavei group species may act as secondary vectors at the edge of the forest reserve, if transmission actually occurs there at all. Our results also suggest that vector control could be feasible because of the vector species breeding in the foothills below 500 m in relatively accessible open country.

Revision of the Ketaketa subcomplex of blackflies of the Simulium damnosum complex.

A revision of the taxonomy of the Ketaketa subcomplex of the Simulium damnosum Theobald complex (Diptera: Simuliidae) is presented including new material from Tanzania, Malawi and South Africa. The cytotaxonomy, morphology and molecular identity of known and new taxa are described. The Ketaketa subcomplex is cytotaxonomically defined by the paracentric inversion 1L-7. We recognize three sibling species, namely Simulium latipollex (Enderlein), Simulium plumbeum Krueger, sp.n. and Simulium kipengere Krueger, sp.n., the latter comprising three cytoforms: 'Typical', 'Linthipe' and 'Mombo'. The cytoforms 'Mwamphanzi', 'Ketaketa' and 'Hammerkopi' are synonymized with S. plumbeum. Identification keys are provided on the basis of chromosomal and morphological characters. In view of their potential role as vectors of human onchocerciasis (river blindness) we also discuss the possible medical importance of the different cytoforms and their geographical distribution.

Impact of ivermectin mass distribution for onchocerciasis control on Ascaris lumbricoides among schoolchildren in Rungwe and Kyela Districts; southwest Tanzania

Across-sectional survey on the impact of ivermectin treatment for onchocerciasis control; on Ascaris lumbricoides infections was conducted in 1994; before the first treatment cycle was implemented in the Tukuyu focus in Tanzania. A total of 560 pupils were randomly selected for stool samples before; 7 days and 3 months after treatment. Modified Kato Katz technique was used to prepare slides; and a dissection microscope for examination. Results showed pre-treatment A. lumbricoides prevalence ranging from 4.2(Lutete) to 34.0(Lufilyo). At day seven post-treatment; samples were devoid of Ascaris eggs; except at Lufilyo with 2.9prevalence. Three months post treatment showed 34 (8.2) out of 213 pupils had patent infections and 24 (5.8) re-infections. Mean infection intensities were significantly higher at pretreatment than three months post-treatment. A. lumbricoides adult worm expulsion was self-reported in the first week of treatment; especially 2-3 days after; by 21.9participants. Ivermectin treatment was effective against adult A. lumbricoides and cleared egg excretion by day seven; but re-infection occurred within three months. Visible worm excretion wasappreciated as potency of treatment. Long term mass treatment with ivermectin proposed for onchocerciasis control can be used to reduce A. lumbircoides infections. To benefit optimally from this programme; additional inputs should be availed to reduce re-infection between consecutive annual cycles. Appreciation of visible worm expulsion enhanced acceptance and compliance of onchocerciasis control campaign using ivermectin. Follow-up surveys are recommended

Descriptions of members of the Simulium damnosum complex (Diptera: Simuliidae) from southern Africa, Ethiopia and Tanzania.

This paper presents cytotaxonomic details of five populations of the Simulium damnosum complex from South Africa, Swaziland and Ethiopia. The 'Nkusi SW' and 'Pienaars' forms are newly designated members of the complex from South Africa, but the taxonomic rank of an isolate indistinguishable chromosomally from the 'Nkusi' cytoform remains unclear. From Ethiopia two cytoforms were identified, one of which shares two diagnostic chromosome inversions with the cytoform 'Kisiwani' from Tanzania. The second form belongs to S. kaffaense, and is the suspected local vector of Onchocerca volvulus. In addition, a re-analysis of the cytoform 'Kibwezi' from north-eastern Tanzania provided further insights into its population subdivision, and its genetic and morphological characteristics. Cytotaxonomic similarities between 'Kibwezi', S. mengense and S. pandanophilum, along with their biogeography, indicate a relict status of each of these taxa.

Malaria in the southern highlands of Tanzania: a review of hospital records.

Outpatient attendance and inpatient admission records were examined to assess malaria situation in ten hospitals in Mbeya and Iringa Regions in southern highlands of Tanzania for a period of fifteen years from 1986-2000. Generally, records were deficient, some hospitals with entire annual records missing for one or several years. However, malaria maintained a high profile as the leading cause of admissions and deaths among hospital attendees. Of the ten hospitals, seven recorded malaria as the leading cause of admissions for at least ten years; in three of these, it was also the top ranking cause of child death. Although the respective magnitude of malaria morbidity and mortality burdens was not directly correlated with altitude (P>0.5), three hospitals (Uwemba, Bulongwa and Ikonda) at above 2,000m, had relatively lower malaria morbidity and mortality burden compared to three worst affected facilities (Ilembula, Chimala and Mbozi) in the lower range of altitude, located in the flat plains. In conclusion, malaria is the major public health problem in the highlands districts of Mbeya and Iringa Regions in Tanzania that need the attention of health authorities and immediate intervention. However, more research is required to establish the true picture of the problem among the communities.

Two new cytoforms of the Simulium damnosum complex (Diptera: Simuliidae) from Malawi and Tanzania and potential onchocerciasis vectors.

During a distribution survey of Simulium damnosum s.l. around the Tukuyu onchocerciasis focus at the northern tip of Lake Malawi/Nyasa (Tanzania), we discovered two new cytoforms of the S. damnosum complex in onchocerciasis-free areas. The Nyika form is related to Simulium thyolense, a vector of onchocerciasis, and can be identified by the new inversion 3L-L on the long arm of chromosome 3. It was found breeding in five rivers in northern Malawi and neighbouring Tanzania and is assumed to be zoophilic. The Njombe form represents a member of the Sanje group of the complex and is characterized by the new diagnostic inversion 2L-35 on chromosome 2. So far, it is only known from around Njombe town in southern Tanzania, where it breeds at remarkably high altitudes. Anthropophily for the Njombe form is well known. The medical importance and systematic position of the new forms within the S. damnosum complex are discussed.

Cytotaxonomy of the Simulium damnosum complex and description of new cytotypes in the Tukuyu focus, southwest Tanzania.

Larvae of Simulium damnosum complex collected from rivers draining Tukuyu onchocerciasis focus were chromosomally examined. Of the 970 larvae analysed, 910 were identified as Kiwira form, a newly described cytotype found in all S. damnosum larval habitats in the Tukuyu area, while 51 were classified as a new subpopulation, tentatively named as Kasyabone form. The F1 larval progeny obtained from wild caught human biting S. damnosum and reared in the laboratory were chromosomally examined. 509 F1 larvae from 70 females blood fed on human volunteers were identified as Kiwira form. As the main human-biting member of the complex in the Tukuyu area, and because some of the wild caught females had developing filarial larvae indistinguishable from those of Onchocerca volvulus, Kiwira form is thus incriminated as the local vector of onchocerciasis. These observations are discussed with respect to previous literature.

Chromosomal diagnostic criteria for some members of Simulium damnosum complex in east Africa.

Identification of Simulium damnosum s.l. vectors of onchocerciasis demands adequate knowledge of the chromosomal features that distinguish human-biting members from nonanthropophilic forms. In this study, 955 S. damnosum larvae collected from various geographical locations in Tanzania were chromosomally analyzed. 358 larvae from small mountain streams in the northeast and central regions of Tanzania, were identified as mainly Nyamagasani and Sanje forms, with only one Kiwira form. 378 larvae from plain and lowland rivers, also in the northeast and central regions, were identified as Nkusi, Kisiwani and Kibwezi forms. Chromosomal examination of 219 larvae from the southern highlands zone revealed the presence of Kiwira and Nyamagasani forms. A further 27 larvae of S. damnosum complex collected from 5 rivers in Uganda were identified as Sebwe and Nkusi forms. Chromosomal photomicrographs on which the distinguishing characters were based are provided. These observations are discussed in the light of previous studies carried out on the S. damnosum cytological forms in Eastern Africa.

Quantitative studies on the transmission of Onchocerca volvulus by Simulium damnosum s.l. in the Tukuyu Valley, South West Tanzania.

A survey of the Simulium breeding and the transmission of Onchocerca volvulus was carried out in and around the Tukuyu valley, S.W. Tanzania, S. damnosum s.l. was found breeding in the midstretches of the main rivers in the valley and their bigger tributaries, and also in the boundary river to Malawi and the most northerly of the three rivers draining the Livingstone Mts. to Lake Nyasa (L. Malawi). A total of 19,500 S. damnosum s.l. females was caught and 13,200 dissected. The annual biting rate varied between 2,000 and 23,800. 7.6% of all the flies were infected with O. volvulus and 1.5% carried infective larvae in the head capsule, on average 2.7 per fly. The transmission was mainly in the dry season and the annual transmission potential varied between 0 and 1,120. The entomological data showed many similarities to those from the Mahenge Mts., Tanzania, and correlation of places with comparable transmission potentials suggests a similarity in the relationship parasite-human host between the West African rain forest and the two Tanzanian foci.