Epidemiology

Global Distribution

Lymphatic filariasis is endemic in 83 countries. India, Indonesia, Nigeria and Bangladesh account for nearly 70% of lymphatic filariasis cases. Other regions include Central Africa, the Nile delta, Pakistan, Sri Lanka, Burma, Thailand, Malaysia, Southern China, the Pacific Islands, Haiti, the Dominican Republic, Guyana, Surinam, French Guiana, and Brazil (Reference 9).

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Important Figures

The at risk population for contraction of lymphatic filariasis includes 1.2 billion people. Currently, more than 120 million people are affected by lymphatic filariasis, including 25 million men who suffer from the genital swellings associated with the disease and 15 million people who suffer from severe lymphodema or elephantiasis of the leg (Reference 10).

The economic burden of lymphatic filariasis is tremendous. Patients who are heavily infected with lymphatic filariasis have a high risk of developing chronic symptoms, including lymphodema and elephantiasis. Such symptoms can result in a decrease in productivity, as they can lead to life-threatening infections if not properly cared for, as well as mobility and functionality problems. In India alone, it is estimated that the annual economic loss due to lymphatic filariasis is $1 billion USD (Reference 11). In nations that are endemic, the economic losses are often not calculated, but likely significant.

Country Information

Nations found to be endemic tend to be tropical or subtropical due to the optimal habitat for the vectors of lymphatic filariasis. Ambient humidity is also necessary for the survival of the infective larva stage of the microfilariae (Reference 12). Populations at high risk for contracting or developing a lymphatic filariasis infection are primarily poor, and a majority of the cases are concentrated in rural areas (Reference 13). Lymphatic filariasis is often associated with areas that have poor sanitation and housing quality (Reference 14). Poorer, rural communities are also typically built around optimal environments for vectors, including marshes or rivers, and tend to lack the resources or capabilities to control for vectors, and transmission is high as a result.

Although there is an established high prevalence of transmission in rural areas of endemic areas, little research has been done around urban transmission of endemic areas. A recent study conducted by a team of epidemiologists from Nigeria and the US looked at the urban area of Jos to find the prevalence of lymphatic filariasis. Although the WHO estimated a low occurrence of less than 1% of urban cases of lymphatic filariasis resulting from urban transmission, this study revealed that approximately 6% of urban cases of lymphatic filariasis were results of urban transmission. According to the authors of this study, and other members of the public health community, this is percentage is high enough to confirm transmission of lymphatic filariasis in urban areas. As a result of this study, a Mass Drug Treatment (MDT) program has been installed in the urban area of Jos, and urban treatment programs such as this are spreading throughout endemic regions (Reference 15).