Identification and control of an isolated, but intense focus of lymphatic filariasis on Satawal Island, Federated States of Micronesia, in 2003

Abstract

BackgroundThere is very limited data available on the prevalence of Bancroftian filariasis in the Federated States of Micronesia (FSM). Considerable attempts to eliminate the disease had occurred in the Pacific region by the year 2003, and the prevalence in FSM was thought to be sufficiently low that the region was considered non-endemic. However, a survey conducted in 2003 on an isolated atoll of FSM, Satawal Island, challenged that assumption.MethodsParticipants on Satawal Island were recruited and their blood tested for Wuchereria bancrofti antigen by the filariasis immunochromatographic test (ICT) card and circulating microfilaria by Knott’s concentration technique. A survey for active cases of lymphoedema, elephantiasis and hydrocoele was performed and mosquitoes were trapped and dissected to detect larvae of W. bancrofti.ResultsA total of 104 males and 149 females from early teens to mid-80s were tested. Men had a significantly higher prevalence of infection than women in both the ICT test (53 vs 28%; p < 0.001) and by Knott’s concentration results (37 vs 11%; p < 0.001). Microfilaria prevalence was higher in subjects ≤25 than in those >25 years of age. All persons sampled were treated for LF. No cases of elephantiasis or hydrocoele were detected. No Aedes dissected were positive but three of nine culicine mosquitoes were positive for L1–3 larval stages of W. bancrofti by microscopy. In depth interviews were conducted with residents and chiefs.ConclusionsThis survey showed that even in regions thought to be close to elimination, isolated high intensity foci of lymphatic filariasis may occur. These need to be recognized and control measures instituted such as local MDA as in the current study.

Detection of Wuchereria bancrofti in the city of São Luís, state of Maranhão, Brazil: New incursion or persisting problem?

“…Analyzing the factors that contribute to the reestablishment of LF transmission by migration, this hypothesis cannot be excluded, especially if the migrants are from endemic areas to areas with unsanitary conditions and where mosquito control measures are lacking [ 32 ]. A similar situation also was identified in a survey by Pretrick in a region in Satawal Island that was thought to have almost achieved the elimination of LF [ 33 ]; in this survey, culicine mosquitoes were found to be positive for W . bancrofti .…”

The History of Bancroftian Lymphatic Filariasis in Australasia and Oceania: Is There a Threat of Re-Occurrence in Mainland Australia?

“…In 2002, a survey of 50 children in a remote atoll of FSM identified 38% as being seropositive. A follow-up survey in the following year also examined adults ( n = 253), finding 38% seropositivity in the whole community and an mf prevalence of 22% [ 93 ]. Transmission was obviously still active at this site, reinforcing the need to continue surveillance in at risk areas.…”

“…Transmission was obviously still active at this site, reinforcing the need to continue surveillance in at risk areas. At the time, the local inhabitants reported an increase in the mosquito population, which may have accounted for the increase in LF transmission—although LF still had to be present in the community for transmission to occur; as a result, the local residents embarked on mosquito control themselves [ 93 ].…”