Lymphatic filariasis (LF), commonly known as elephantiasis, is a neglected tropical disease. Infections occur when filarial parasites of Wuchereria or Brugia genera are transmitted to humans by mosquitoes1. Wuchereria bancrofti is the most common and causes 90% of all the lymphatic filariasis infections worldwide. Infection is usually acquired in childhood and is the second cause of chronic global deformity that impairs the lymphatics, leading to long-lasting disability2. Chronic manifestations of the disease include lymphedema, elephantiasis and genital deformities3. In 2020, 863 million people in 50 countries were living in areas that required preventive chemotherapy to stop the spread of the infections. The global baseline estimates of people affected by lymphatic filariasis was 25 million men with hydrocele and over 15 million people with lymphoedema. At least 36 million people remain with these chronic disease manifestations1.
Lymphatic filariasis is a major cause of morbidity, severely affecting socio-economic development in endemic areas 4,5 . Prior to MDA programs in 2000, it was estimate that lymphatic filariasis contributed to 5.25 million disability- adjusted life years (DALYs), which dropped to 2 million DALYs by the year 2016 6 . Individuals suffering from lymphatic filariasis experience repeated filarial attacks known as adenolymphangitis (ADL), which hinder them from actively participating in social and economic activities 7,8 . The economic burden due to filariasis in the US alone amounts to $5.765 billion annually 9 of which $114.69 is associated to the chronic manifestations and acute attacks of the disease 9,10 . Studies have shown that 83% of the total economic loss is due to disability in men with hydrocele coupled with the fact that young adults contribute more to economic development 11 . In Africa, lymphatic filariasis causes almost US $1 billion loss each year 12. The morbidity also causes burden to individuals, household, government-funded and private healthcare systems 13,14 . The surgical management of hydrocele cases in hospitals causes strain to already overburdened health-delivery systems 15 . Genital damage in men causes severe handicap leading to physical limitations and social stigmatization. In women, lymphedema of the lower limbs and genital parts enlargement is shame and taboos and are considered undesirable. Affected women feel severely stigmatized and marriage in many situations becomes unstable with separations or even impossible for the youths 16 . In many cases, chronic lymphatic filariasis patients require constant care and attention becoming a burden to the rest of the family members. School going children also fail to attend schools due to morbidity caused by lymphatic filariasis and sometimes leading to many cases of school drop-outs 12 .
The World Health Assembly (WHA) Resolution 50.29 in 1997 called for elimination of lymphatic filariasis as a public health problem. Following the resolution, WHO initiated the Global Programme to Eliminate Lymphatic Filariasis (GPELF) by the year 202015,6. The GPELF proposed a comprehensive elimination strategy, including (i) transmission interruption in endemic communities by use of mass drug administration (MDA) to entire at-risk population and (ii) implementation of interventions to prevent and manage lymphatic filariasis-associated disabilities (Morbidity Management and Disability Prevention (MMDP) strategy). Parasite transmission interruption can be achieved with MDA coverage at 80–90% in the intervention units for over 5 to 6 years or longer in areas with high baseline microfilaria (mf) prevalence. Annual MDA reduces the density of parasites in circulating blood of the infected people to levels where transmissions can no longer be sustained by mosquito vector17. For MDA interventions, single dose of 2 anthelminthic drug combinations is administered: albendazole (ALB) (400 mg) + diethylcarbamazine (DEC) citrate (6 mg/kg); ALB (400 mg) + ivermectin (IVM) (150–200 µg/kg) or 3 drugs in combination (ALB + DEC + IVM) to all at risk population in endemic regions. There has been significant progress in the control of lymphatic filariasis by the GPELF with over 8.6 billion cumulative treatments delivered to stop the spread of infection since the start of the Program in 2000. However, in practice this has been insufficient in many endemic countries where pockets of hotspots persist even after 10 or more rounds of treatment as reported in Ghana18. By 2018, 24 lymphatic filariasis endemic countries (of 83) no longer required MDA and were conducting post-MDA surveillance, global estimation of people requiring MDA dropped from 1.4 billion in 2011 to 492 million in 2020 due to successful implementation of WHO strategies18,19,20. To achieve the second goal of GPELF, a core strategy of Morbidity Management and Disability Prevention (MMDP) is needed. Suffering caused by the disease can be alleviated through a minimum recommended package of care to manage chronic stages; lymphedema, elephantiasis and hydrocele. These services should be made available in primary health care systems in all endemic regions.
Despite all the efforts by the Programme, elimination in many countries had not been achieved in 2020 as anticipated earlier, therefore a new road map for Neglected tropical diseases elimination was re-drawn targeting elimination by the year 2030 with intensified and integrated control intervention1.
Kenya, an endemic country, launched its National Programme for Elimination of Lymphatic Filariasis (NPELF) in 2002 in Kilifi District and extended the Programme to Malindi and Kwale Districts in 2003. By 2011, only four rounds of MDA had been given in some districts with significant decrease in prevalence, while other districts such as Tana River had received only one round22,23. The MDA programs in Kenya is under the Division of Vector-Borne and Neglected Tropical Diseases, (DVB-NTD) in the Ministry of Health. The implementation is guided by the Kenya NTD breaking transmission strategy, 2019–2023. The plan is to expand MDA coverage, implement Water, Sanitation, and Hygiene (WASH) interventions and implement Behavior Change Communication (BCC) as a comprehensive package24. There is need for the endemic countries which are about to reach the elimination target to do a comprehensive assessment for re-mapping, monitoring and evaluating the impact control of the programs in place.
Lymphatic filariasis has been documented in Kenya since 191025. Comprehensive mapping of the disease in Kenya was done between 1998 and 1999 during which only coastal region was found to have prevalence that could be termed as endemic according to WHO guidelines26,6,1. To date, the disease remains endemic in coastal regions of Kwale, Mombasa, Malindi, Kilifi, Tana River, Lamu and Taita Taveta23. About 2.5 million people in Kenya are at risk of infection23,27. All control efforts have been directed and scaled up only in the regions where the disease has been found to be endemic27. There are however strong speculations of lymphatic filariasis circulations in other regions including Lake Victoria region particularly in Kisii, Kisumu and Western Kenya Counties. Recently, presence of circulating filarial antigens was detected in patients around Lake Victoria region (N. Kinyatta, unpublished data) indicating that other regions of the country are at risk of the disease. Furthermore, factors such as destructive ecological and land use practices and climate changes have been known to shift the geographic ranges of vectors thus increasing the risk of disease transmission. Increased temperatures also increase the reproduction rates and shorten pathogen incubation periods within vectors resulting in increased transmission.
The western part of Kenya is susceptible to filarial infections due to its proximity to Lake Victoria and Uganda which is lymphatic filariasis endemic area. In addition, the climate of this region favors mosquito vectors capable of transmitting filariasis. A number of lymphatic filariasis infection cases have been reported in Busia and some referred to KEMRI-Alupe for diagnosis (Busia referral hospital records; N. Kinyatta, personal communication). World Health Organization recommends that a prevalence of more than 1% filarial antigenaemia and 2% microfilaremia be considered endemic6. Kenya and many other endemic countries had not attained a prevalence threshold to be declared free from lymphatic filariasis infections by the year 2020 as earlier proposed27,23. Thus, more MDA rounds and scaling up to other susceptible regions was recommended. Several gaps however exist that need to be bridged before the National programme for elimination of lymphatic filariasis (NPELF) declares Kenya free from filarial infections. For example, mass screening of other suspected regions needs to be carried out and to have NPLEF extended to the affected regions. Provision of diagnostic tools for surveillance and Morbidity Management and Disability Prevention (MMDP) interventions is also required. This study aimed at screening lymphatic filariasis in Busia County in Kenya through human and mosquito infections assessment so as to provide additional information to what is already documented for filariasis from other at-risk regions. The study will thus generate critical data on infections in the region that will advise policy makers, Ministry of Health, NPELF and other stakeholders on the need to embark on the necessary control efforts in the region with the overall goal of moving closer to Kenya being declared free from lymphatic filariasis infections.