prevent ova sinking. Similarly, they argue that flotation methods suffer
from a number of disadvantages which is reflected in the extreme variation
in the enumeration results when using this method. Some flotation fluids
can foam and trap the ova and compost debris can drag ova to the bottom.
Their favoured approach for enumerating Ascaris ova in composts is the
filtering method using the Visser filter.
A demonstration of this method waspresented at a dry sanitation workshop attended by the author in San Salvador, El Salvador, in January,
1996.
For viability determination it was recommended that ova are placed into a
shallow solution of
0.1
N sulphuric acid or0.5%
formalin in a cottonstoppered Erlenmeyer flask and then incubated in the dark at 22°C for three weeks.
3.3.3
Enumeration and at theWHO
Centre .
One of the few places conducting research into
Trichuris trichiura
is a groupat the Well come Centre for the Epidemiology of Infectious Disease, Department of Zoology and WHO Collaborating Centre, University of
Oxford in the United Kingdom.
In 1996, the group was conducting human
immunoepidemiological research using
Trichuris
ova and larvae. Aftergrinding, oxantel (adult female worms) are sieved through a simple tea strainer to isolate the ova which are then scraped from the underside of the
sieve. Ova are then washed and re-suspended in
0.25%
formalin and distilledwater before transferring to wide-bottomed tissue culture flasks. The flasks allow for an adequate oxygen supply during incubation. The flasks are then
stored in the dark at ambient temperature (Pers. comm. Needham,
1996).
Itwas decided to adapt this method in
1998 for the final stages of this research
study as described in section
•
3.4.5
(c). It was deemed appropriate to utilize this procedure because of itssimplicity and the fact that this group were actually working with
Trichuris
rather than
Ascaris.
3.3.4
assessment of toilet theand Health Studies Pakistan
Useful discussions and an exchange of information took place with
microbiologists at the Water, Sanitation, Hygiene and Health Studies Project (WSHHSP) laboratories in Gilgit and Skardu, Baltistan during the research
visit to the Northern Areas of Pakistan (Chapter
2.4.1).
Tasks performed bythe team of microbiologists assessing latrine compost included:
• odour from the compost chamber on opening;
• presence of flies;
• temperature of the centre of the pile;
• appearance of the compost; 108
• number of Ascaris lumbricoides ova per gram of compost sample; • number of Ascaris lumbricoides ova per gram of sample; • pH;
• moisture content; and
• bacteriological examination for faecal coliforms (Collett
1995: 3).
Direct sampling, flotation techniques and the modified formol-ether concentration procedure for detecting and enumerating Ascaris lumbricoideswere used by WSlffiSP in their field laboratories. The most consistent recovery was obtained using the modified formol-ether process. Viability of ova was determined by observing their morphological characteristics and the activity of larva within the egg after embryonation. Determining larva activity was achieved through irritation of the larva using
1%
sodium hypochlorite solution (bleach powder) (Raza and Abbas1996;
Ahmed et al.1995).
This method of inducing larval motility in embryonated Ascarislumbricoides ova was first described by Smith
(1991: 760)
and was utilized by both Moody (Pers. comm.17
December,1996)
and Needham (Pers. comm.14 March, 1996).
A suggestion was made to the author for incubating Trichuris trichiura ova based on advice given to the microbiologists at WSHHSP by Tony Moody from the Department of Parasitology, Hospital for Tropical Diseases, London. He visited Gilgit in
1995
to train the microbiologists in laboratory techniques and field investigation procedures relating to the health aspects ofexcreta management systems. Moody recommended using a charcoal
culture for detecting larvae of Strongyloides and hookworm in human stool (Fleck and Moody
1988: 35)
. The suggestion was made to adapt this technique for incubating Trichuris ova. It was also recommended to use a method for incubating helminth ova that had been observed by a WSlffiSP microbiologist at the International Centre for Diarrhoeal Disease Research in Bangladesh. Helminth ova are incubated in1%
Hydrochloric acid at ambient temperature over7
days in50
mL pyrex containers, in the dark,. and without a lid. The ova are checked every24
hours (Pers. comm. Raza1996).
Also of interest was the method used for collecting samples of compost from latrines in Gilgit and Baltistan. PVC pipe is used to
insert
into the pile to the required depth. The pipe is then removed and the section containing the core sample required is cut off with a hacksaw.Results from the parasite testing of compost from traditional latrines and Twin Pit Composting Latrines (TPCL) located throughout Gilgit and Baltistan
indicate that many of the compost samples still contain viable
Ascaris
ova,particularly manure from wetter latrines which sometimes have high percentages of ova.
3.3.5 Parasite in Vietnam
According to members of staff at the Parasite Department of the Institute for Research Tropical Medical, Bac Mai Hospital in Hanoi, Vietnam,
approximately 30% of the people in the north and only 3% of people in the south of the country were infected with
Trichuris trichiura24•
Direct morphological methods are used for identifying human intestinal nematodes. There are many kinds of parasites in Vietnam. As in most medical contexts, the main focus at the Institute is on the identification of any parasite present in the stool samples of patients. Chemotherapy is then used to eliminate the infection in the host. A ten step system is used to determine the viability of parasite ova based on morphological observation. One method used to determine ova viability is to place the ova intoBaragallo (H20 + formalin) at the rate of 8.5mL of formalin to 1 000 mL of
water. The other solution that has been used is Ringer solution which is used as a drip in the hospital and comes in sealed plastic drip containers. It was suggested that ova should embryonate in 2-7 days at ambient temperature in Ringer solution. Compost samples are taken from different levels in the latrine when inspecting for ova presence. Sometimes broken fluorescent tubes are used to extract samples from the latrines, using a different tube for collecting each level of sample (Pers. comm. Dr Nguyen Van Tien and Dr. Kieu Tung Lam 12 October, 1996).
3.3.6 The Method for ova
This method was developed for identifying, quantifying and determining the viability status of helminth ova in solid and semi-solid samples. The process uses a combination of.sedimentation and flotation techniques incorporating an acid-alcohol/ ether extraction step before the concentrate is incubated at 26°C until embryonation takes place (Pers. comm. Schwartzbrod 6
24 UNICEF, Hanoi
claims that Ascaris
infection is 114% in the north and 40% in the south andhookwonn infection is 60% in the North and 25% in the South (Pers. comm. Quynh. 9 October, 19%).