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Title: Preventive chemotherapy for elimination of lymphatic filariasis and onchocerciasis in Sierra Leone
Author: Koroma, J. B.
ISNI:       0000 0004 6425 3672
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Lymphatic filariasis (LF) and onchocerciasis are highly endemic in Sierra Leone. Using World Health Organization (WHO) guidelines for monitoring national programmes where both infections are co-endemic, this study aimed to determine the impact of preventive chemotherapy on transmission intensity by measuring changes in human infection status using standard epidemiological indicators. Separate longitudinal studies designed to deliver WHO outcomes for programmes targeting the elimination of both diseases were conducted. Onchocerciasis mapping surveys from 1988-2005 revealed that twelve of fourteen health districts were endemic. The baseline average mf prevalence was 53.1%, and mf densities in positive-only or entire populations were 28.87 and 15.33 mf/snip, respectively. Mf prevalence and density increased with age and was higher in males than females. Baseline prevalence and intensity surveys showed that LF was endemic in all 14 districts (Wuchereria bancrofti antigenaemia prevalence > 1%). Mean LF prevalence by ICT cards was 21% (males 28%; females 15%) with higher prevalence in the northeast (Bombali 52%; Koinadugu 46%; Tonkolili 37%; Kono 30%) and lower in the southwest (Bonthe 3%; Pujehun 4%). Mf prevalence was also relatively higher in the northeast (Bombali 6.7%; Koinadugu 5.7%; Port Loko 4.4%; Kono 2.4%). Mf prevalence was higher in males (males 2.9%; females 1.8%) and infection rate was higher in the over 20 years age-group (2.5%) than younger (1.7%). Arithmetic mean mf density was 50.30 mf/ml among mf-positive individuals and 1.19 mf/ml in the population examined. Nationwide mass drug administration (MDA) using ivermectin plus albendazole was applied to eliminate both diseases. In 2010, after five rounds of MDA (2005-2009) with effective treatment coverage for onchocerciasis during 4/5 years, overall onchocerciasis mf prevalence was reduced by 60.26% (from 53.10% to 21.10%), overall mf density among positive-only individuals was reduced by 71.29% (28.87 to 8.29 mf/snip) and overall mf density among the entire population studied was reduced by 88.58% (15.33 to 1.75 mf/snip). Mf prevalence and density were higher in males, lowest in the 1-9 and highest in the 40-49 year age groups. Mf prevalence was reduced by >50% in 10/12 districts, and reduction in skin mf density was ≥50% among positives-only in 11/12 districts. After MDAs with effective treatment coverage in 2008-2010, LF mf prevalence decreased to less than 1% in 11/12 districts. Mf prevalence fell by 88.5% to 0.3%, with decreases of 70-95% in seven and 100% (0 prevalence) in four districts, respectively. Overall arithmetic mean mf density after three MDAs was 17.59 mf/ml among mf positive individuals and 0.05 mf/ml for the entire population examined. After five MDAs, the overall mf prevalence was 0.54% and was higher in males (0.7%) than females (0.36%). Eight of twelve districts with < 1% mf prevalence passed the pre-transmission assessment survey (TAS) and therefore qualified for a TAS to determine whether MDA could be stopped. Four districts failed the pre-TAS: Koinadugu (0.98% i.e. close to 1%), Bombali (2.67%), Kailahun (1.56%) and Kenema (0%). Following WHO recommendations, Kenema and Kailahun districts were paired to form a unit of approximately one million. Kenema, the spot check site, was considered to have failed the pre-TAS even though the mf prevalence was 0% because Kailahun, the sentinel site, failed. A qualitative study examining the impact of the Ebola virus disease (EVD) outbreak on the NTD programme found that despite a one-year absence of interventions, two rounds of MDA had been completed, including one during the ongoing outbreak in May/June 2015. Although it compromised the likelihood of achieving the 2020 targets of LF elimination and Onchocerciasis control, the EVD outbreak has enhanced awareness about the important role of community volunteers in ensuring its success. While it may be the ‘endgame’ for LF, the NTD community and collaborating research institutions must address additional challenges if Onchocerciasis is to be eliminated from Sierra Leone.
Supervisor: McCall, P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral