Reinfection of people with Ascaris lumbricoides following single, 6-month and 12-month interval mass chemotherapy in Okpo village, rural Burma

Abstract

A longitudinal study on reinfection with Ascaris lumbricoides was continued on a random sample of 50% of the infected population following a horizontal cross-sectional study in Okpo village, near Rangoon. The study sample was again randomly divided into two subsamples, the six-month interval worming group and the 12-month interval worming group. Microscopic examination of stool for Ascaris eggs on the 7th day and 30th day, combined with counting eggs and worming with levamisole, were carried out at two successive six-month intervals on the first subsample. Stools were examined and eggs counted on the 7th day and then monthly up to 12 months, followed by worming, in the second subsample. The worms expelled in the first 72 hours after treatment were counted. The findings over a 12-month follow-up period after one treatment included: mean monthly incidence of 20%, higher and more rapid return to previous prevalence and intensity of infection in children or 'wormy' persons than in adults or 'non-wormy' persons. Six-monthly chemotherapy definitely reduced intensity of infection in the children and adults whereas 12-monthly treatment lowered intensity in adults only. Predisposition to acquisition of high or low intensity of infection was also observed. Other findings and the implications of this study for strategies for control of ascariasis are discussed.

Can chemotherapy alone eliminate the transmission of soil transmitted helminths?

“…Once R 0  > 2 some of either adults, pre-SAC or both must be treated as well at high coverage levels (Figure  3b,c,e,f). In most settings where Ascaris and/or Trichuris are prevalent, R 0 exceeds 2.5 in value [31,32]. Treating both SAC and pre-SAC, as sometimes carried out by control programmes, with high coverage (>80%) results in good suppression but the ‘breakpoint’ is not crossed.…”

The Impact of a School-Based Hygiene, Water Quality and Sanitation Intervention on Soil-Transmitted Helminth Reinfection: A Cluster-Randomized Trial

“…Although the impact of the intervention on A. lumbricoides reinfection was substantial and significant, we cannot rule out that our findings are a consequence of baseline imbalances and differential rate patterns of reinfection between study arms. We expect that infection would revert to baseline levels in as few as 6 months [42][43][44] ; our follow-up was 10 months after deworming. However, we saw a secular trend of decreased prevalence of helminth infection among children in control schools.…”

Patterns of soil-transmitted helminth infection and impact of four-monthly albendazole treatments in preschool children from semi-urban communities in Nigeria: a double-blind placebo-controlled randomised trial

“…Prevalence is regarded as a relatively insensitive measure of reinfection because of the aggregated distribution of worms per child [9]. It has been well documented that marked changes in intensity may be accompanied by only small changes in prevalence [35-37]. Furthermore, because of high rates of reinfection in endemic regions the aim of deworming is not to reduce prevalence but to reduce morbidity by decreasing worm burden.…”