Parasitological surveillance

The primary method used to identify filaria patients in Sri Lanka is Night Blood Filming (NBF). This involves examining thick blood smear slides under a microscope to detect microfilaria in the blood film. The microfilaria (mf) rate serves as the main indicator and is calculated accordingly:

The graph illustrates the microfilaria rate (mf) in endemic districts in Sri Lanka from 1981-2024. Throughout this period, the mf rate in the country has consistently remained below<1%. In 1997, the first Mass Drug Administration (MDA) was conducted as a pilot project using Diethylcarbamizine Citrate (DEC). Subsequently, in 2000, another MDA was implemented in endemic areas. From 2002-2006, an MDA was carried out in endemic districts using DEC and Albendazole.

The graph demonstrates a decrease in the mf rate in the country between 2010-2012, following the MDAs. However, there was a temporary increase in the mf rate in 2013 and 2014, primarily due to a higher number of cases reported in the Galle district. As a response, an MDA was conducted in the Galle district by AFC.

Since the 1980s, the mf rate in Sri Lanka has consistently remained below 1%. Consequently, Sri Lanka was recognized by the World Health Organization (WHO) in 2016 as a country that has eliminated lymphatic filariasis as public health problem. After 2016, the mf rate remained below 0.05%, while the mf rate recorded as 0.0047% in 2024.

Prior to 2016, screening for filariasis was primarily conducted within local communities. However, Anti Filariasis Campaign (AFC) recognized the risk of disease transmission through the immigrant workers and identified them as a significant threat. Consequently, in 2016, a new strategy was implemented to target the immigrant worker community by conducting screening at their work places.

In 2019, in collaboration with the Health Ministry and the International Organization for Migrants (IOM), AFC successfully incorporated filariasis testing in to the visa process for immigrant workers.

This involved utilizing filaria antigen test kits to detect filariasis, specifically bancroftian filariasis. Positive cases were then referred to AFC for appropriate treatment.