Ascaris suum: nutrient absorption, growth, and intestinal pathology in young pigs experimentally infected with 15-day-old larvae

Thymus-independent crypt hyperplasia and villous atrophy in the small intestine of mice infected with the trematode Echinostoma revolutum

Conventional mice and congenitally athymic, nude mice were infected with 20 metacercariae of the intestinal trematode Echinostoma revolutum. The sequential events in the pathological changes in the intestine were studied at different intervals post-infection. By day 11 onwards the conventional mice displayed dilatation of the region of the intestine which harboured the parasites. The mucosa in the dilated region showed marked crypt hyperplasia, villous atrophy and subepithelial fibrosis as the most conspicuous features which, together with a hypertrophy of the muscular layers, made the wall of the gut in the dilated region thicker than normal. The changes were thymus-independent as they were found to be as severe in the athymic, nude mice as in the conventional mice. The main histological features observed in the mice are discussed in relation to other conditions with similar changes, such as coeliac disease, nippostrongyliasis and trichinellosis. It is concluded that the present results support the view that there may be more than one effector mechanism of the change.

Methods to evaluate nutritional and economic implications of Ascaris infection

Ascaris infection has important economic implications for human populations, due to its negative effects on growth of undernourished children and its less common role in causing intestinal obstruction. The deleterious effects of Ascaris infection on growth of undernourished children have been demonstrated in studies conducted in India, Kenya and Tanzania; deworming has resulted in improved weight gains of 20-35% compared with uninfected children. However other studies in Ethiopia, Bangladesh and Guatemala have not found statistically significant improvements in growth of children after treatment for Ascaris infection, most likely due to inadequacies in choice of population, sample size, experimental design, data analysis and/or relative failure of drug treatment. Field studies which attempt to measure the magnitude of growth deficits due to Ascaris must take the following into account: (1) rapidly growing preschool age children from communities with a high prevalence of protein-energy malnutrition are the most important group to study. (2) A longitudinal design, preferably using randomly allocated treatment and placebo groups, is highly desirable. (3) A sufficient period of time for growth improvement must be allowed between the beginning of the intervention and final measurements. (4) The sample sizes necessary to test hypotheses adequately should be calculated in advance. (5) The drug chosen for treatment of Ascaris should produce high cure rates and reinfection rates should be determined. Possible effects of the drug on other diseases prevalent in the population should be considered in the data analysis. (6) Evaluation of worm loads are very important in interpretation of results. (7) The data analysis must be appropriate for the individual study and must be designed to consider confounding factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Eimeria tenella: cecal contraction in infected chickens

The muscle of ceca from chickens infected with Eimeria tenella had an increased amplitude of contraction when compared to the cecal muscle of uninfected control chickens. The increased amplitude was significant (P less than or equal to 0.05) at 5 days postinoculation (PI) and became nonsignificant at 7 days PI. The amplitude also increased with the severity of the infection. The sensitivity of the muscle from infected ceca to acetylcholine (ACH) was greater than the control. Infection by different strains of E. tenella also increased the sensitivity of the cecal muscle to ACH when compared to the uninfected control. The rate of spontaneous contractions was not different in any group or treatment. The wet weight of infected ceca increased with days PI and severity of infection.

The contribution of Ascaris limbricoides to malnutrition in children

There is a need for more applied and experimental research to determine more precisely the relationships between nutrition, particularly childhood malnutrition, and intestinal parasitic infections, particularly Ascaris infection. Nevertheless, it is clear that in certain communities Ascaris infection is associated with poor growth in malnourished children and that deworming improves growth. Periodic deworming of children using a mass treatment approach may be needed to control soil-transmitted helminths in areas where parasites and protein energy malnutrition are highly prevalent. The main aims of treatment should be to reduce parasite loads below the level of clinical significance for the individual child and to reduce future environmental contamination with infective faeces for the sake of the community.