The interruption of transmission of onchocerciasis in Kaduna, Kebbi and Zamfara states, Nigeria: another milestone achievement.

BACKGROUND: More than 40 million people live in onchocerciasis-endemic areas in Nigeria. For at least 19 y, mass drug administration (MDA) with ivermectin was implemented with at least 65% total population coverage in Kaduna, Kebbi and Zamfara states. Impact surveys done using skin biopsies yielded no infections. Serological and entomological assessments were undertaken to determine if onchocerciasis transmission had been interrupted and MDA could be stopped. METHODS: The presence of onchocerciasis-specific immunoglobulin G4 antibody was measured by enzyme=linked immunosorbent assay conducted on dried blood spots collected from 5- to 9-year-old children resident in each state. O-150 polymerase chain reaction testing of Simulium damnosum s.l. heads for Onchocerca volvulus DNA was done on black flies collected by human landing capture and Esperanza window traps. RESULTS: A total of 9078 children were surveyed across the three states. A total of 6139 vectors were collected from Kaduna state, 129 from Kebbi state and 2 from Zamfara state; all were negative. Kebbi and Zamfara states did thousands of hours of black fly catching and intensive river prospecting. The resulting low fly catch was due to a low fly population incapable of sustaining transmission. CONCLUSION: Onchocerciasis transmission has been interrupted and the three states meet World Health Organization thresholds: seropositivity in children <0.1% and <1/2000 infective black flies with 95% confidence. The 2.2 million people in Kaduna state and 4 million in Kebbi and Zamfara states no longer need ivermectin for onchocerciasis.

Assessing Hypoendemic Onchocerciasis in Loa loa Endemic Areas of Southeast Nigeria.

Nigeria changed its goal for onchocerciasis from control to transmission elimination. Under the control program, ivermectin mass drug administration (MDA) focused only on hyper/meso-endemic local government areas (LGAs) identified by Rapid Epidemiological Mapping of Onchocerciasis as having ≥ 20% nodule rates. Because transmission is likely in some LGAs where nodule rates are < 20%, the new elimination paradigm requires MDA expansion. Determining which hypoendemic areas require MDA, termed onchocerciasis elimination mapping, is a major challenge. In 2016, we studied 19 ivermectin-naive hypoendemic LGAs in southern Nigeria that bordered LGAs under MDA. Fifty adults and 50 children (aged 5-10 years) were tested in 110 villages for onchocerciasis IgG4 antibody using an Ov16 rapid diagnostic test (RDT). A 10% subset of subjects provided a blood spot for confirmatory Ov16 ELISA. The mean prevalence of RDT positives was 0.5% in the 5,276 children tested (village range, 0.0-4.0%) versus 3.3% in 5,302 adults (village range, 0.0-58.0%). There was 99.3% agreement between the Ov16 RDT and ELISA. Six different MDA launch thresholds were applied to the RDT results based on different recommendations by the Nigeria Onchocerciasis Elimination Committee and the Onchocerciasis Technical Advisory Subgroup of the WHO. Mass drug administration targets for the same area varied tenfold by threshold chosen, from one LGA (population to be treated 221,935) to 13 LGAs (population 2,426,987). Because the Ov16 threshold selected will have considerable cost and resource implications, the decision to initiate MDA should incorporate entomological data demonstrating onchocerciasis transmission.

In Southern Nigeria Loa loa Blood Microfilaria Density is Very Low Even in Areas with High Prevalence of Loiasis: Results of a Survey Using the New LoaScope Technology.

Ivermectin treatment can cause central nervous system adverse events (CNS-AEs) in persons with very high-density Loa loa microfilaremia (≥ 30,000 mf/mL blood). Hypoendemic onchocerciasis areas where L. loa is endemic have been excluded from ivermectin mass drug administration programs (MDA) because of the concern for CNS AEs. The rapid assessment procedure for L. loa (RAPLOA) is a questionnaire survey to assess history of eye worm. If ≥ 40% of respondents report eye worm, this correlates with ≥ 2% prevalence of very high-density loiasis microfilaremia, posing an unacceptable risk of CNS-AEs after MDA. In 2016, we conducted a L. loa study in 110 ivermectin-naïve, suspected onchocerciasis hypoendemic villages in southern Nigeria. In previous RAPLOA surveys these villages had prevalences between 10% and 67%. We examined 10,605 residents using the LoaScope, a cell phone-based imaging device for rapidly determining the microfilaria (mf) density of L. loa infections. The mean L. loa village mf prevalence was 6.3% (range 0-29%) and the mean individual mf count among positives was 326 mf/mL. The maximum individual mf count was only 11,429 mf/mL, and among 2,748 persons sampled from the 28 villages with ≥ 40% RAPLOA, the ≥ 2% threshold of very high Loa mf density could be excluded with high statistical confidence (P < 0.01). These findings indicate that ivermectin MDA can be delivered in this area with extremely low risk of L. loa-related CNS-AEs. We also concluded that in Nigeria the RAPLOA survey methodology is not predictive of ≥ 2% prevalence of very high-density L. loa microfilaremia.

The role of national committees in eliminating onchocerciasis.

National onchocerciasis elimination committees (NOECs) serve to help ministries of health complete the pathway to successful verification of elimination of onchocerciasis (river blindness), as outlined in the 2016 World Health Organization guidelines. These guidelines, however, only take effect when the country believes it has reached a point that elimination can be demonstrated, and do not address the preceding milestones. Therefore, NOECs can be of great help with guiding and tailoring earlier planning, programming and assessments to empower national programs to aggressively move toward their countries' elimination goals. In this article, we provide suggestions for organizing NOECs and examples of four such committees that have successfully operated in Africa and the Americas.

The geographic distribution of onchocerciasis in the 20 participating countries of the African Programme for Onchocerciasis Control: (1) priority areas for ivermectin treatment.

BACKGROUND: The African Programme for Onchocerciasis Control (APOC) was created to control onchocerciasis as a public health problem in 20 African countries. Its main strategy is community directed treatment with ivermectin. In order to identify all high risk areas where ivermectin treatment was needed, APOC used Rapid Epidemiological Mapping of Onchocerciasis (REMO). REMO has now been virtually completed and we report the results in two articles. The present article reports the mapping of high risk areas where onchocerciasis was a public health problem. The companion article reports the results of a geostatistical analysis of the REMO data to map endemicity levels and estimate the number infected. METHODS: REMO consists of three stages: exclusion of areas that are unsuitable for the vector, selection of sample villages to be surveyed in each river basin, and examination of 30 to 50 adults for the presence of palpable onchocercal nodules in each selected village. The survey results and other relevant information were processed in a geographical information system. A panel of experts interpreted the data taking the river-based sampling into account and delineated high risk areas where the prevalence of nodules is greater than 20%. RESULTS: Unsuitable areas were identified in eight countries. In the remaining areas surveys were done in a total of 14,473 sample villages in which more than half a million people were examined. High-risk areas were identified in 18 APOC countries, ranging from small isolated foci to a vast contiguous endemic area of 2 million km2 running across seven countries. In five countries the high risk area covered more than 48% of the total surface area, and 31% to 48% of the population. It is estimated that 86 million people live in high risk areas in the APOC countries. CONCLUSIONS: The REMO maps have played a significant role in onchocerciasis control in the 20 APOC countries. All high-risk areas where onchocerciasis used to be a serious public health problem have been clearly delineated. This led to the creation of community-directed treatment projects that by 2012 were providing annual ivermectin treatment to over 80 million people.

Community-wide distribution of long-lasting insecticidal nets can halt transmission of lymphatic filariasis in southeastern Nigeria.

Lymphatic filariasis (LF) in rural southeastern Nigeria is transmitted mainly by Anopheles spp. mosquitoes. Potential coinfection with Loa loa in this area has prevented use of ivermectin in the mass drug administration (MDA) strategy for LF elimination because of potential severe adverse L. loa-related reactions. This study determined if long-lasting insecticidal net (LLIN) distribution programs for malaria would interrupt LF transmission in such areas, without need for MDA. Monthly entomologic monitoring was conducted in sentinel villages before and after LLIN distribution to all households and all age groups (full coverage) in two districts, and to pregnant women and children less than five years of age in the other two districts. No change in human LF microfilaremia prevalence was observed, but mosquito studies showed a statistically significant decrease in LF infection and infectivity with full-coverage LLIN distribution. We conclude that LF transmission can be halted in southeastern Nigeria by full-coverage LLIN distribution, without MDA.

Epidemiology of tree-hole breeding mosquitoes in the tropical rainforest of Imo State, south-east Nigeria.

The study of tree-hole breeding mosquitoes was carried out in the tropical rainforest of Imo State Nigeria (two rural areas and two forest reserves in some parts of Orlu Senatorial Zone) between May-October 2002. Using standard entomological procedures, two macrohabitats (natural tree-holes and bamboo traps) and two microhabitats (leaf axils of cocoyams/pineapples and leaf axils of plantain/banana) were sampled for various mosquito species. Mosquitoes were recovered from all the various biotypes sampled. Types of mosquitoes species encountered, their relative abundance, as well as genera varied significantly during the study (p<0.05). Four genera of mosquitoes: Aedes, Culex, Anopheles and Toxorhynchites were recovered while 16 species of mosquitoes encountered include: Aedes aegypti, Ae. africanus, Ae. simpsoni, Ae. albopictus, Ae. stokesi, Ae. taylori, Ae. apicoargenteus, Culex quinquefasciatus, Cx. nebulosus, Cx. trigripes, Cx. decens, Anopheles gambiae, An. funiestus, An. coustani and Toxorhynchites viridibasis. Most of the mosquitoes showed oviposition preferences for one or more habitats. The presence of Ae. africanus, Ae. simpsoni and Ae. aegypti indicate that the study areas were at risk of yellow fever epidemic. The presence of Anopheles and Culex species ensured endemicity of malaria and filariasis, while the recovery of Ae. albopictus in this region suggests a possible outbreak of dengue fever in future if not properly controlled.

Clinical and parasitological aspects of onchocercal skin diseases in Nigeria.

An assessment of onchocercal skin disease (OSD) conducted in 38 rural communities in the Imo River Basin, Nigeria, between March 1999 and September 2000, showed that depigmentation (DPM) was the most prevalent lesion in persons with skin microfilariae (mf) (26.3%), followed by chronic papular onchodermatitis (CPOD) (18.1%) and acute papular onchodermatitis (APOD) (15.5%). There was no significant difference (P > 0.05) in sex-related prevalence of OSD. While CPOD, lichenified onchodermatitis (LOD) and DPM were more prevalent in subjects over 30 years old, APOD was associated more with those aged less than 30 years. OSD occurred with concomitant itching in nearly 50% of subjects. The geometric mean intensity of infection was 13 mf/mg per skin snip.

Prevalence of Mansonella perstans infections among the nomadic Fulanis of northern Nigeria.

The study was undertaken to investigate the prevalence and clinical manifestations of Mansonella perstans infection in the nomadic Fulanis of northern Nigeria. Physical examination of 755 consenting nomads for clinical manifestations of M. perstans infection was carried out between June 1996-September 2000. This was followed by parasitological examination of blood samples collected by finger prick method to identify microfilariae (mf). Data collected was stratified by locality, age and sex, and analyzed using the Chi-square test. Overall, 66 (8.7 %) of 755 nomads were infected. Infection was higher in men (9.7 %) than in women (6.5 %) (p<0.05) and occurred in all age groups with highest prevalence in persons in the 4th (14.1 %) and 5th (17.1 %) decades of life. Fifty-six (81.8 %) of the 66 nomads with mf had clinical manifestations with periodic dizziness (18.2 %), body itching (15.2 %) was the most prevalent while back pain (7.6 %) was the least. The findings show that mansonelliasis is an important health problem in nomads. This underscores the need to establish a well-articulated Filariasis Control Programme for this group whose major health problems are rooted in their occupation and amplified by several contingencies of the environment.

Prevalence of parasitic diseases among nomadic Fulanis of south-eastern Nigeria.

A study was carried out to determine the prevalence of parasitic infections among the nomadic Fulanis of south-eastern Nigeria between September 2003-March 2004. Urine, stool and blood specimens were collected from each of 231 subjects. Of these, 98 (42.4%) were infected with one or more of 14 parasitic species, of which Plasmodium malariae had the highest prevalence (15.3%). Others included 6 intestinal helminth parasites: Ascaris lumbricoides, hookworm, Strongyloides stercoralis, Schistosoma mansoni, Enterobius vermicularis, Trichocephalus trichiurus, 2 protozoan parasites: Entamoeba histolytica and E. coli, 4 blood parasites: Mansonella perstans, Loa loa, Trypanosoma sp, Plasmodium falciparum, as well as Schistosoma haematobium recovered in the urine. Prevalence of these parasitic infections varied significantly among bush encampments, sexes, and age groups. They had evidence of onchocerciasis. Their occupational imperatives, beliefs and general life style are contributing factors to the prevalence of parasitic infections among the nomadic Fulanis of south eastern Nigeria. Aspects of prevalence and control of parasitic infections are discussed.

Endemicity of vesical schistosomiasis in the Ebonyi Benue river valley, south eastern Nigeria.

The investigation on the prevalence of patent and clinically severe infections with Schistosoma haematobium was carried out amongst inhabitants of Ebonyi Benue river valley, South Eastern Nigeria between August 2000 and June 2001. The inhabitants are predominantly farmers. Of the 3296 subjects examined from 15 randomly selected villages in the valley, 776 (23.5%) were excreting the eggs of S. haematobium in their urine. Infection rates varied between 18.9% and 30.6%. The severity of infection calculated by arithmetic mean egg counts (AMEC) and geometric mean egg counts (GMEC) varied significantly between the age groups and the villages (P < 0.05). The prevalence and severity of infection increased with age from 0 to 25 years and decreased thereafter. Symptoms associated with the disease include visible hematuria (63.1%), suprapubic pain (10.3%) and stranguary (9.9%). While 65 positive persons had more than one symptom, 64 of the positive persons had no noticeable symptoms. Visible hematuria showed moderate sensitivity and high specificity for the disease. Female genital schistosomiasis (FGS) of the lower reproductive tract was recorded in 19 females of child bearing age that complained of severe suprapubic pain. Eight snail species were recorded in the stagnant ponds and both Bulinus globosus and B. truncatus were infected with schistosome cercariae. The factors contributing to these observations and feasible control measures are discussed.

Dracunculiasis in the north eastern border of Ebonyi State, south eastern Nigeria.

Between January and August 2000, a house-to-house survey of dracunculiasis was conducted in 15 communities along the north eastern border of Ebonyi State, south eastern Nigeria. Of the 3,777 subjects examined, 192 (5.1%) had active cases of guinea worm comprising 109 males (5.5%) and 83 females (4.6%). Infections were observed in all age groups. Of the 3,777 persons examined, 2,092 (55.4%) had ever been infected in the area. Protruding adult female Dracunculus medinensis worms were found predominantly on the lower limbs (80.2%), but also on the scrotum (9.4%), umbilicus (3.1%) groin (2.6%), buttocks (20.8%) and chest (1.6%). Prevalence of dracunculiasis had no significant sex, age and occupation related differences (P > 0.1). All the 47 stagnant ponds in the area were infested with cyclops while the 6 streams and 13 newly constructed community wells were free of cyclops. Of the five species of cyclopoid copepods found in the stagnant ponds, only Thermocyclops oblongatus nigerianus and Mesocyclops aequatorialis harboured guinea worm larvae. The efforts of the endemic communities, government and international organizations in guinea worm eradication in these areas are discussed.