LYMPHATIC FILARIASIS
The prevalence of intestinal parasitoses and lymphatic filariasis in the Corentyne Region of Guyana. (A7)
Introduction
Lymphatic Filariasis (LF) is a debilitating, disfiguring infection (Figure) caused by the parasitic nematode Wuchereria bancrofti. The parasite occurs in over 80 countries worldwide and an estimated 120 million people are currently thought to be infected; the majority of cases being in sub-Saharan Africa and Asia. It is increasingly being recognized as an infection contracted in childhood with the disfiguring morbidity evolving slowly and manifesting in older age groups.
In 1997 the World Health Assembly resolved to eliminate LF as a public health problem by 2020. This resolution was made feasible by recent advances in research which had shown that ivermectin and DEC were extremely effective microfilaricides with a long residual suppressive effect on their own and increasingly so with the addition of albendazole.
This revelation, together with the development of a new sensitive, specific immunochromographic (ICT) diagnostic test which only requires a few drops of blood taken at any time of the day provided the tools to make eradication practical. The magnanimous donation by GlaxoSmithKline (albendazole) and Merck (ivermectin – for Africa only) to the program for as long as the global effort takes, coupled to donations from Foundations, international bodies provides great optimism for the parasites demise as a public health problem throughout the world. This possibility is greatly enhanced by the greater understanding of the cause of morbidity associated with the parasite and new treatment methods which have been shown to be remarkably effective.
In the Americas, seven countries are considered to be still endemic for LF although the disease has not been seen in three (Suriname, Costa Rica and Trinidad) for the last 20 years. Active transmission occurs in four countries, Guyana, Haiti, Dominican Republic and Brazil. For the program objectives for the elimination of LF (PELF). LF is not regarded as being a problem in Trinidad and Tobago, Suriname, or Costa Rica and in these countries surveillance and confirmation of the disappearance of the parasite has to be carried out using the ICT test mapping program. An active PELF is now required for the endemic countries and the choice of control program is being studied.
Guidelines for preparing and implementing a national plan to eliminate LF in countries where onchocerciasis is not endemic have been produced by WHO. These guidelines are being followed by the LF endemic countries in the Americas. Most countries have created National Task Forces (NTF-ELF), and are in the process of choosing the best intervention approach, given the unique characteristics in each endemic country. An initial mapping exercise using ICT test cards is to be used by each country and this study was to examine the prevalence of LF in a rural area of Guyana. Since albendazole may be one of the treatment choices this study also aimed to examine the prevalence of the geohelminths in the same region of rural Guyana. Soil transmitted helminths are increasingly being recognized as an important public health problem, especially in developing countries.
The group that harbors the heaviest infection rates, as well as the worst cases of morbidity is school age children. In 1993, the World Bank ranked intestinal helminths as the number one cause of disease burden in children between the ages of 5 and 14 (www.WorldBank.org). During the years of 1995 and 1996, worm infestation was ranked as the second leading cause of morbidity among children in the 0=<4 year range according to the World Health Organization. In 1998, intestinal parasites not only claimed nearly two million lives under the age of five, but also accounted for 1.5 billion bouts of illness in children under five in developing countries.
The hypothesis of this study was that in rural Guyana intestinal helminths would be very prevalent whilst LF would have a low prevalence compared to urban areas. If this hypothesis turned out to be correct then using albendazole in rural areas would have a dual benefit for the local population.
Materials and Methods
Region VI in rural Guyana, a Heavily Indebted Poor Country (HIPC), was selected as an ideal site for the study. Four primary schools in a community in Berbice were selected for study. The work was cleared through WINDREF’s IRB and subsequently through the Ministries of Health and Education in Guyana. Schools were visited and several parent teachers meetings were held to discuss the goal of the study and what it involved. Informed consent was obtained from all who participated in the study. Stool collection cups were given to children and returned with a stool specimen the next day.
Blood samples were taken from children and parents in the same area. All samples were transported to a lab in Georgetown and stored until tested. The blood samples were tested using the ICT test cards provided by CDC. Stool samples were flown to the WINDREF laboratory in Grenada on ice and tested using the salt (hypertonic saline - NaCl) floatation technique. A questionnaire was administered to all participants to examine risk factors. The questionnaire was pre-tested and local terms were applied. Because of dialect differences, the questionnaire was administered by Guyanese trained laboratory staff.
Results
None of the 200 stool samples collected and tested were positive for geohelminths (hookworm, Ascaris lumbricoides or Trichuris trichuria). The results of the ICT test cards is presented in the Table below.
| Age Range | No. Tested | No. Positive | % Positive |
| 12-13 | 179 | 1 | 4.5 |
| 14-20 | 20 | 1 | 3.4 |
| 21-30 | 22 | 0 | 0.0 |
| 31-40 | 27 | 1 | 3.7 |
| 41-50 | 26 | 2 | 7.7 |
| 50+ | 21 | 2 | 9.5 |
| Total | 295 | 14 | 4.8 |
Table: Age prevalence of the blood samples tested for Wuchereria bancrofti.
Discussion
The prevalence of LF in the community did show a gradual increase with age (Table). The overall prevalence was far lower that the > 45% reported from Georgetown. Another study in Georgetown and New Amsterdam found prevalences of 30% and 20% respectively. The prevalence of LF appears to be much lower in rural Guyana as expected. The reasons for this may be the smaller human population, which is spread out and lower transmission infection pressure. Certainly breeding sites (particularly pit latrines for Culex quinquefasciatus which is likely to be the major vector) are numerous.
The fewer number of people infected may contribute to the lower transmission pressure. The negative geohelminth result is surprising. It was noted that the Rotary club of Virginia had recently completed a mass treatment program with albendazole for schoolchildren in the region and this may have been a contributory factor. This fact was not reflected in the answers given in the questionnaire which asked about treatment in the previous months. Albendazole is available in the shops and education is given high value in this community. As elsewhere in the Caribbean treatment of children for worms at the start of the school year is done. Since the introduction of albendazole in the mid eighties the prevalence of intestinal helminths has been falling in many Caribbean nations and they now occur at low levels. Whatever the reason our hypothesis for this aspect had to be rejected and the alternate accepted.
Dr Ramsammy (Minister of Health, Guyana), Dr Macpherson discuss the outcome of the study carried out by Jessica Morlock and Sean Ramsammy (research scientists).
A regional LF meeting hosted by PAHO in Georgetown in 2001 helped determine the choice of elimination strategy to be employed by the local Task Force in Guyana. Ivermectin is to be reserved for use in Africa. Distribution of DEC and albendazole has its own drawbacks in a country where the population is not easily accessible, especially in remote, rural areas. A further option of the use of DEC-fortified salt was suggested and accepted. The feasibility of this approach is due mainly to the fact that there are only 2 suppliers of salt to Guyana: these being Jamaica and Trinidad. Thus strict control on the importation of only fortified salt can be achieved.
The product has a long shelf life, has no odor, is tasteless, is not destroyed by cooking and is effective against the microfilariae at low doses for prolonged periods of time. DEC-fortified salt was in fact the control approach used so successfully by the Chinese to eliminate LF in China. The use of this approach will mean that the intestinal helminths will not be affected. The low prevalence found in this study, however, suggests that local rural populations are taking care of this problem by themselves – at least in our study population.
