The effects of physical and chemical factors on the development of eggs of Ascaris lumbricoides and Trichuris trichiura

Abstract

The study was done in the Parasitology Laboratory at the Department of Medical Microbiology of the University of Nairobi. It was an invitro experimental study. Also the development of eggs (segmentation and embryonation) in the external soil environment and their occurrence in a natural peridomestic urban environment were studied. The objective was to study the effects of various physical and chemical factors on the development of eggs of Ascaris lumbrocides and Trichuris trichiura. Positive stool specimens for eggs of Ascaris lumbrocides and/or Trichuris trichiura were identified from the collected and examined stool specimens of the patients at the Kenyatta National Hospital. Also soil specimens were collected and examined for similar eggs from two underprivileged areas in Nairobi. stool specimens were re-examined and confirmed microscopically using the formal-ether concentration (FEC) method by the Principal investigator and a senior laboratory technologist. The positives were pooled together and analyzed in bulk. also included. Control samples were The experiments done included the incubation of the stool samples in different physical and chemical conditions such as temperature, humidity, acidity and alkalinity. Samples were incubated for a duration of five weeks. They were examined weekly for egg development. These were then counted and recorded

~developed, segmented or embryonated. As described in the results, Ascaris lumbricoides eggs were majority and Trichuris trichiura eggs were few. The results how that for the temperatures (22 to 28uc) studied, development eggs was best at 28JC, less well at 37°C and not at The eggs developed at room temperature better than 37~ under similar conditions. The eggs developed better in acidic conditions compared to alkaline ones. The eggs developed in both 4% and 10% formalin solutions but better in the former solution. The eggs developed in conditions of adequate moisture but not in those without moisture. In general, development of eggs was better aerobically than anaerobically except in 10% formalin solution. In most of the experiments, the proportion of eggs developed was highest at week three and thereafter declined in weeks 4 and 5.This was more evident under alkaline conditions and at 37cC. The results of egg development in the external soil environment showed that about one sixth of the eggs developed.The eggs seen and identified from examination of soil collected in the urban periaomestic environment were of Ascaris lumbricoides and few of them were segmented or embryonated.