A practical strategy for responding to a case of lymphatic filariasis post-elimination in Pacific Islands

Lymphatic filariasis (LF) due to Wuchereria bancrofti is being eliminated from Oceania under the Pacific Elimination of Lymphatic Filariasis Programme. LF was endemic in Solomon Islands but in the 2010-2020 Strategic Plan of the Global Programme to Eliminate LF, Solomon Islands was listed as non-endemic for LF. In countries now declared free of LF an important question is what monitoring strategy should be used to detect any residual foci of LF?

The index case, a 44 year old male, presented to Atoifi Adventist Hospital, Malaita, Solomon Islands in April 2011 with elephantiasis of the lower leg. Persistent swelling had commenced 16 months previously. He was negative for antigen by TropBio Og4C3 ELISA and for microfilaria. A week later a survey of 197 people aged from 1 year to 68 years was conducted at Alasi, the index case's village, by a research team from Atoifi Adventist Hospital and Atoifi College of Nursing. This represented 66.3% of the village population. Blood was collected between 22:00 and 03:00 by finger-prick and made into thick smears to detect microfilaria and collected onto filter paper for W. bancrofti antigen tests. A second group of 110 specimens was similarly collected from residents of the Hospital campus and inpatients. W. bancrofti antigen was tested for using the Trop-Bio Og4C3 test.

One sample (1/307) from an 18 year old male from Alsai was positive for W. bancrofti antigen. No samples were positive for microfilaria. Although antigen-positivity indicated a live worm, the case was regarded as having been acquired some years previously.

We propose that when LF has been eliminated from a country, a case of elephantiasis should be a trigger to conduct a survey of the case's community using a decision pathway. W. bancrofti antigen should be tested for with screening for microfilariae in antigen positive cases. The field survey was designed and conducted by local researchers, highlighting the value of local research capacity in remote areas.