Yemen eliminates LF as a public health problem

01 Ago 2019

Yemen eliminate lymphatic filariasis as public health problem

Congratulations to Yemen as it becomes the second country in the Eastern Mediterranean Region of the World Health Organization (WHO) to eliminate lymphatic filariasis (LF) as a public health problem joining other countries already validated by WHO as achieving the criteria.

This landmark achievement in a particularly challenging environment brings hope in improving the health of future generations.

Special recognition is made here to Dr Abdul Samid Al-Kubati who has been crucial in his unfailing dedication in leading the national programme to its success.

The National Programme to Eliminate Lymphatic Filariasis (PELF) was established in 2000 to address the dual goals of mass drug administration (MDA) and morbidity management and disease prevention (MMDP) on a national scale following the World Health Assembly resolution (WHA 50.97) on LF that called for its global elimination by 2020.

Yemen’s success comes after almost two decades of tremendous efforts of sustained elimination measures as recommended by WHO of the two pillars (MDA and MMDP) of the Global Programme to Eliminate Lymphatic Filariasis (GPELF) strategy.  After several rounds of MDA implementation, surveys since 2011 have validated that infection has been reduced to below transmission thresholds.

Transmission assessment surveys (TAS) conducted in 2013 and 2016 confirmed that Yemen had met all criteria for achieving elimination as a public health problem while, at the same time, management of morbidity in affected patients continued. Yemen will continue to improve its morbidity management programme treating patients with clinical symptoms as well as maintaing the appropriate level of surveillance to ensure continued zero transmission.

The achievements of the Yemen PELF were made possible through the generous support and funding from the World Health Organization (WHO), the integration with the national leprosy programme (NLEP), the generous drug donations from the Mectizan Donation Program and GSK and the generous technical guidance of GPELF-WHO and GAELF. 

LF in Yemen

Lymphatic filariasis (LF) in Yemen was probably not documented in ancient times. A description from Aden of clinical cases of lymphoedema suggests that the disease may have been present as early as the past century. Filariasis due to Wuchereria bancrofti was recognized as a public health problem on Socotra Island in 2000, and Culex quenquifasciatus was found in 2005 to be the major mosquito vector of the disease. The national Programme for the Elimination of Lymphatic Filariasis (PELF) was established in 2000 for LF control and elimination integrating with  National Leprosy Elimination Programme (NLEP).

During 2000–2001, a nationwide mapping survey was conducted to determine the extent of LF as a public health problem in a lot quality assurance survey of the immunochromatographic test (ICT) for LF antigenaemia. Surveys were conducted in all 22 governorates, in districts selected according to criteria that included indicators of clinical cases and responses to questionnaires. District sectors, ozlas, were selected for mass drug administration (MDA), and over 20,000 ICTs were performed. The survey indicated that LF was focally endemic in rural and semi-urban localities and was concentrated in the semi-urban area of Socotra Island governorate, mainly in the Hedibo area (40% antigenaemia). The prevalence of antigenaemia was >1% in six other governorates (Taiz, Ibb, Al-Hudydah, Dhamar, Abyan and Shabwah). The other governorates were free of LF. Thus, eight implementation units (IUs) in seven governorates, including Socotra Island, were found to be endemic for LF. Aridity in mountainous areas, use of waste water in rural areas and urbanization appear to have prevented LF in most areas of Yemen, in addition to treatment of clinical lymphoedema and sowda (localized onchocerciasis) with diethylcarbamazine citrate and later with ivermectin (Mectizan®) in many areas of the country. The National Leprosy Elimination Programme (NLEP) extended treatment of sowda with ivermectin in the western governorates with voluntary MDA, vector control by residual house spraying and larviciding, which may also have resulted in a considerable decrease in the prevalence of the disease and later played some role in the elimination of LF.

LF had a predominantly focal distribution; however, night blood sampling and microscopic examination for microfilariae were inadequate in most health facilities, and the results could not be used to determine the endemicity of the disease, even though the environmental, social and agricultural features appeared suitable. The Ministry of Public Health had no registry of LF-endemic areas. In 2000, Yemen joined WHO global efforts to eliminate LF as a public health problem and initiated the national PELF. The Programme had two main objectives: to interrupt LF transmission by delivering single annual doses of ivermectin plus albendazole to the entire eligible population living in areas where the disease is endemic (≥1% antigenaemia) and to alleviate the suffering caused by LF by morbidity management and disability prevention (MMDP). The aim was to achieve an MDA coverage rate of >65% of the total population in each IU. The programme components for interrupting transmission were mapping eligible IUs; training primary health care (PHC) physicians, nurses and health workers in the IUs in drug distribution; social mobilization through various formal and informal channels to deliver clear messages; directly observed drug distribution; treatment of adverse reactions; and monitoring and evaluation of MDA rounds.

Annual MDA rounds were conducted in 2002–2006, each round being followed by evaluation of the coverage rate, which confirmed effective coverage and provided insight into the perception of the populations of the campaigns. In order to monitor the effect of MDA on LF infection, the PELF determined the prevalence of microfilariae at sentinel sites and by spot-checks 1 month before the third, fourth, fifth and sixth rounds of MDA. After two rounds, the microfilariae prevalence rate was 0 at all sentinel sites except on Socotra (>1%; baseline 6%); however, the rate on Socotra had decreased to 0 after eight MDA rounds.

The criteria for stopping MDA had been met by 2006. Consequently, a fifth MDA round was implemented in December 2006, followed by  stopping-MDA surveys according to 2005 WHO guidelines. After evaluation of stopping-MDA surveys in 2008, MDA was stopped in all IUs on the mainland, six of which had received five effective MDA rounds. MDA was continued on Socotra, with some supplementary vector control measures. By the end of 2011, another microfilaraemia survey and TAS showed no microfilaraemia or antigenaemia, and MDA was stopped on Socotra Island. The impact of MDA on LF infection was monitored by the PELF in sentinel surveys and at spot-check sites, which showed that nine annual MDA campaigns with ivermectin plus albendazole had probably eliminated LF from Yemen.

In 2013, 6 years after MDA had been discontinued in the mainland IUs and 2 years after it had been discontinued in Socotra, a second TAS was conducted. None of the schoolchildren tested was ICT-positive. The third TAS was conducted in 2016 with filariasis test strips (FTS), which also gave negative results.

For MMDP, leprosy health care workers in NELP clinics, located all over the country as part of the PHC system, have been treating people with lymphoedema since the beginning of the LF programme in 2000. The personnel have been trained to care for chronically affected patients, who receive the minimal package of health care for lymphoedema management, health care aids, drugs and information booklets.

Thus, from its inception, the PELF took all the necessary measures to control and eliminate LF, with mapping, mass treatment with ivermectin plus albendazole, vector control by residual house spraying and larviciding, distribution of long-lasting impregnated bed nets near breeding sites of C. quenquifasciatus (the main vector on Socotra) and MMDP for clinical lymphoedema cases. The third TAS indicated that LF has probably been eliminated from Yemen.

Dr Abdul Samid Al-Kubati

NFP-Filariasis

Taiz-Yemen

Mobile: 00967 771292029

E-mail: a-samidku [at] hotmail [dot] com