Worm expulsions

Update by Rita Oliveira, PhD student, Imperial College London

The community-based baseline parasitological survey was completed in Kwale County just in time for the National School-Based Deworming Programme to administer albendazole to all school-age children in the county, which took place on the 4th June 2015. The survey provided info on the prevalence of soil-transmitted helminths (STH) in the county, and revealed hookworm to be the most prevalent species in the area, followed by Trichuris trichiura (whipworm) and Ascaris lumbricoides (roundworm).

Following treatment with albendazole, infected individuals pass dying worms in their stool over a few days. Collecting and counting these worms provides a direct measurement of the actual burden of infection that each person carries. This contrasts with the indirect measurement made during the parasitological survey, which is based on parasite egg counts, which are also passed in stool during infection. Individual information on both the number of eggs per gram of stool (EPG) and the number of worms expelled following treatment allows us to obtain an estimate of eggs per worm, which in turn allows us to better estimate the burden of infection in future egg counts. Knowing these details can improve the control of soil-transmitted helminths (STH), particularly as it will improve predictions of the efficacy of deworming programmes and, thus, the design of control programmes.

Activities

For the TUMIKIA worm expulsion study, three clusters were selected based on their STH prevalence, one with high, one with medium and one with low hookworm prevalence. Following the school-based deworming, 120 school-age children from each cluster (a total of 360) were randomly selected to collect whole stool output over a period of six days, starting on the day following deworming. The children were required to store all their stools in a recipient, which was collected and replaced daily by their village’s community health workers. These recipients were then taken to three laboratories, where technicians would sieve them to collect, count and store any worms present.

A group of 24 local and national lab technicians (3 teams of 8) were trained on the techniques required for hookworm collection from whole stool samples. In short, it involves sieving stools through sieves with openings consecutively smaller, to obtain a fine residue with (possibly) hookworms. This residue is then placed in a tray and carefully searched for worms. This is required due to the very small size of adult hookworms, with males usually 5 to 9mm long and females about 1cm long. Any possible worms found are then checked under the microscope to confirm identification and gender – important since only female worms produce eggs. All hookworms from a single individual are then stored in a labelled tube and kept frozen.

Following training, technicians carried out a parasitological survey of the 300 selected children on the day of deworming treatment. This provided a recent measurement of eggs per gram of stool for each child, to be compared with worm numbers in the following days.
Over the following six days each team of 8 technicians, organized in working pairs, sieved through 100 whole stools per day collected by the community health workers in each cluster and successfully recovered not only hookworms but also roundworms, whipworms and a large number of pinworms.

Challenges

The main challenges faced by any worm expulsion study are:

  1. Compliance – many people feel uncomfortable collecting and storing their whole stools, and might be unwilling to keep participating over the course of the collection period. Fortunately, most children were willing to comply and kept providing their stools over the 6 days.
  2. Manual labour and thoroughness required – hookworms are very small and whole stools are usually composed of many fibres which are similar in size and shape to worms. Carefully searching through a whole stool requires time, patience and good eyesight, as well as a certain tolerance to foul smells.

Next steps

Community-based treatment is scheduled to take place in the villages involved in the TUMIKIA study from mid-July, in collaboration with EvidenceAction. In the three clusters involved in the worm expulsion studies a total of 840 pre-school children and adults (280 per cluster) were also randomly selected to provide whole stools over five days. This will take place over 2 weeks, with half of the participants being treated on the first deworming day and providing stools over the first week and the other half being treated and collecting stools on the second week. This will ensure that each technician team will have a manageable number of recipients (120 to 140) to be checked each day.

This section of the population, in particular the adults, are expected to harbour a larger number of hookworms than school-age children, not only because school-age children have been dewormed at school in previous years, but also because hookworm infection burden tends to increase with age in any given community – it is still not completely understood why, but it might be related to a more prolonged exposure to infection while farming barefoot in contaminated fields.

 

Lab work:

 

 

 

Trichuris worm collected from pot:

 

Lab team. Rita is in the middle:

 

One of the rural villages taking part in the study: