Viability of Ascaris and other helminth genera non larval eggs in different conditions of temperature, lime (pH) and humidity

Abstract

Helminth eggs are the pathogens most resistant to inactivation during sludge and wastewater treatment. For this reason, in several regulations and the WHO guidelines for wastewater and excreta reuse for agriculture and aquaculture they are considered as indicators of the performance of the treatment process. Conditions required to inactivate helminth eggs, notably Ascaris lumbricoides, are recommended in the literature, but in practice these have not always proven effective, not only for Ascaris but also other genera of helminth eggs. The objective of this research was to study the inactivation of a high total content of non larval Ascaris and other genera of helminth eggs of medical importance to developing countries under controlled conditions of (a) temperature (30 °C to 80 °C) and humidity (80, 90 and 95%) and (b) lime doses (15 and 20% of CaO w/w dry basis) and humidity (90 and 80%), using different contact times in both cases. The inactivation data obtained for different genera of non larval helminth eggs is presented. Results showed that there is a combination of conditions (temperature, pH and humidity) that is optimal for inactivation. To completely inactivate any genera of non larval helminth eggs: (a) a temperature above 70 °C and 80% humidity for a duration of 120 min; and, (b) a 20% CaO dose (pH 12.5) and a humidity level of 80% for a duration of 8 months are needed. With regard to the resistance of different genera of helminth eggs, Ascaris, Toxocara and Taenia, in that order, were the most resistant, while the most sensitive were Trichuris and Hymenolepis. For most of the conditions tested Ascaris showed the highest resistance, probably due to the chemical arrangement of its membrane.

Comparison of methodologies for enumerating and detecting the viability of Ascaris eggs in sewage sludge by standard incubation-microscopy, the BacLight Live/Dead viability assay and other vital dyes

“…Eggs of A. suum are morphologically indistinguishable from eggs of A. lumbricoides and the two species exhibit similar w a t e r r e s e a r c h 6 8 ( 2 0 1 5 ) 5 3 3 e5 4 4 resistance to environmental stress (Maya et al, 2010). Moreover, eggs of A. suum are readily available in sufficient quantities for experimental purposes and are safer to handle in the laboratory than eggs of A. lumbricoides, as A. suum rarely infects humans (Nejsum et al, 2012).…”

Environmental tolerance of free-living stages of the poultry roundworm Ascaridia galli

“…On the other hand, according to Maya et al (2010), pH of 12.5 and 80% humidity for a duration of 8 months is needed to completely inactivate any genera of non-larval helminthes eggs. Despite the fact that development continued at all different pH levels, Lazdina and Grinberga (1978) noted that prolonged preservation of the A. galli eggs in acid media considerably inhibits the establishment of the A. galli in the chicken.…”

Physicochemical and parasitological quality of vegetables irrigation water in Ouagadougou city, Burkina-Faso

“…In general, available evidence indicates that helminthes eggs are more resistance to environmental stresses than protozoan cysts. This can be attributed to the fact that helminthes eggs have strong membrane with several layers acting as barriers to environment condition (Maya et al, 2010). Contrary to Escherichia coli that shows no viable cysts, E. histolytica presented high rate of viable cyst.…”