RESUMO
As part of the Pacific Program to Eliminate Lymphatic Filariasis (PacELF), baseline surveys were conducted in 1999 and 2004 in Nauru to determine the prevalence of filariasis by rapid immunochromatotraphic test (ICT). In 1999, the survey demonstrated a filariasis prevalence of 0.26%, and Nauru was classified as a non-endemic country at the time. In 2004, the prevalence resulting from the survey was 1.66%. Since it exceeded 1.0%, this high prevalence warranted the implementation of Mass Drug Administration (MDA) according to WHO guidelines and gave rise to an urgent need to re-establish the filariasis policy in Nauru, as the target year for filariasis elimination in the Pacific is 2010. The present study was conducted to determine the current prevalence of filariasis, to decide whether implementation of the MDA program is necessary, and to compare the demographic characteristics of participants according to the ICT test results. Blood sampling and interviews, based on a simple questionnaire asking about filariasis-related symptoms, were conducted by trained health staff members. A total of 1,513 people were enrolled for the survey in January 2007. Filariasis positivitiy was detected in three subjects (0.2%) by ICT test. Nauru was reconfirmed as a non-endemic country and therefore did not require the MDA implementation. The prevalence did not vary significantly according to the demographic characteristics. The three seropositive cases did not have any filariasis-related symptoms. However, two of the three positive cases of filariasis lived in the same district and the other lived in a neighboring district. To assess the interruption of filariasis transmission, further surveys are recommended.
RESUMO
<I>Background</I><br>Samoa was formerly highly endemic for Wuchereria bancrofti filariasis transmitted by Aedes mosquitoes. Previous control efforts including sporadic mass drug administration (MDA) campaigns have reduced the prevalence to low levels but have not succeeded in eliminating the disease. To effectively plan, model and evaluate the worldwide elimination effort, the Global Programme to Eliminate Lymphatic Filariasis (GPFLF) needs data on filariasis epidemiology (including age and sex-specific prevalence and the density of microfilariae (Mf)) and estimates of the number of years of MDA required for elimination. The five-year nationwide MDA campaign carried out in Samoa before the start of the Pacific Programme to Eliminate Lymphatic Filariasis (PacELF) generated extensive data on these issues.<br><I>Methodology⁄Principal Findings</I><br>MDA campaigns were conducted in Samoa with diethylcarbamazine (DEC) in 1993 to 1995 and DEC plus ivermectin in 1996 to 1997 for all persons aged 2 years and above. Coverage of the MDA, as assessed from the campaign village register books, ranged from 62% to 97% depending on the year, and was over 80% in three out of five years. Village based surveys showed that prevalence of Mf declined from 4.3% in 1993 (N=10,256) to 1.1% in 1998 (N=4,054) (Pχ<SUP>2</SUP>=94.4, p<0.001). Males had a three- to five-fold higher prevalence than females, and this difference remained consistent over the five-year period. Transmission was still occurring over the period as shown by the occurrence of new infections in 3 children less than 5 years old out of 5,691 tested (five-year cumulative incidence of 0.53 per thousand children for the period 1993 to 1998). There was a statistically significant reduction in the geometric mean number of Mf per 60 μl in positive cases between 1993 (11.8) and 1998 (6.9) (t=2.61; p<0.01). The proportion of people with a high density of Mf - over 60 Mf per 60 μl (1000 per ml) - declined from to 19.4% to 4.0% (Pχ<SUP>2</SUP>=5.6, p=0.018).<I><br>Conclusions⁄Significance</I><br>Five years of sustained MDA with DEC (3 years) and DEC plus ivermectin (2 years) reduced the prevalence of Mf of <I>W.bancrofti</I> in Samoa by 74%. Density of Mf in infected individuals was also significantly reduced. Males had a three to five-fold higher prevalence than women. New infections in children less than five years old still occurred at a low level, suggesting that transmission was not completely interrupted. These findings helped to prepare a sound monitoring and evaluation plan for PacELF.