Current WHO protocols for mass drug administration in helminth control

Soil transmitted helminths (STH), comprising Ascaris, Trichuris, Strongyloides and the hookworms remain a significant cause of morbidity amongst people in many parts of the world, including Australia. Other important helminth infections include lymphatic filariasis (LF), schistosomiasis and onchocerciasis. Preventive chemotherapy (mass drug administration [MDA]) campaigns are frequently conducted for these helminth infections in endemic areas, but the target population groups, duration of campaigns, cointerventions (e.g. vector control) criteria for inclusion, drugs used and doses of drugs differ.

The benefits of deworming individuals, especially children, who are infected with soil-transmitted helminths and schistosomiasis, include reduction in anaemia and improved growth. Rarer, but more severe presentations, such as intestinal obstruction with A. lumbricoides and rectal prolapse due to T. trichiura infection, will also be reduced¹. Treatment for filariasis and onchcocerciasis in childhood will prevent the development of later severe consequences of these diseases including lymphoedema, hydrocoele, elephantiasis and blindness.

In situations of moderate to high endemicity, it has been considered more efficient and cost-effective to treat the entire eligible population in particular age groups or communities for these diseases, rather than first testing individuals to determine who is infected. The goals of such MDA are morbidity control in some cases and interruption of transmission through vectors in others. For these reasons, MDA for STH is usually undertaken for school age children, while for schistosomiasis, MDA is performed either in children or in eligible people of all ages, depending on the endemicity level. For the insect borne helminths, onchocerciasis and LF, the goal is transmission interruption and the entire community is eligible for MDA.

The frequency of MDA for STH in school-age children is dependent on the prevalence of infections in a given population (Table 1). Current WHO protocols for STH control recommend MDA with a single oral dose of albendazole (400 mg), mebendazole (500 mg) or levamisole (80 mg)¹. Mebendazole is more effective than albendazole for T. trichiura, whilst albendazole is slightly more effective against hookworm than mebendazole. The two drugs have equally high efficacy when used against Ascaris lumbricoides¹. Despite these differences, in practice when administered biennially over a number of years, either drug used on its own is effective for overall STH control¹.

Table 1. Current recommended regularity of mass drug administration (MDA) for helminth (STH) infections in school-age^A children (adapted from WHO 2011)¹.

Onchocerciasis control and/or elimination requires annual or biannual treatment with ivermectin for many years (up to 20 in some cases), while lymphatic filariasis uses annual administration with albendazole and either ivermectin or diethylcarbamazine (DEC) with at least 65% population coverage for at least five years. Thus ivermectin and/or albendazole administration may occur in some communities annually or biannually as part of onchocerciasis or LF elimination programs. Where this occurs, STH control programs should be harmonised to ensure that there is a 6 month delay between albendazole administrations¹. In communities with endemic schistosomiasis, the addition of praziquantel (40 mg/kg) is recommended (Table 1). Reductions in the frequency of MDA may be considered after 5–6 years of consistent >75% population coverage, after testing of the residual prevalence of helminths in that population. Such a decision is based on several factors, specific details of which may be found in the World Health Organization guide for managers of control programmes¹.

Reliance on albendazole and mebendazole in WHO recommendations for MDA will result in a lower impact on the clearance of Strongyloides stercoralis, for which ivermectin and thiabendazole are more effective drugs². Thiabendazole was discontinued in Australia in 2003 and due to the lower rate of side effects, ivermectin has been recommended by some as the treatment of choice². Due to the auto-infective cycle of this helminth, some authors have recommended re-treatment at one and two months to ensure elimination³. Only one randomised trial has been performed thus far, in which treatment twice at 2 weeks apart was found to have no greater benefit than a single dose⁴. Both the authors of this paper and others² recommend further studies into the optimal dose schedules for ivermectin in the control of Strongyloidiasis within a larger cohort of participants.

Recently, there has been discussion about the outcomes and optimal age range for MDA programs to control STH and more evidence on the impacts is required^5–7; this controversy is outside the scope of this review. A novel concept of elimination of STH by MDA ‘one village at a time’ rather than by wide-scale MDA has been proposed for remote areas with low populations, such as many remote Australian Aboriginal communities. This approach is currently being trialled in a remote area of the Solomon Islands⁸. It advocates allowing individual communities to act as autonomous units and to employ control options specifically tailored to the geographic, cultural, economic, aetiological and environmental factors influencing STH transmission in their own community⁸ (Figure 1).

Figure 1. A Solomon Islander researcher undertaking a community wide STH prevalence survey as part of an integrated STH control program (photograph by Richard Bradbury).

Deworming of school-age children has been a mainstay of helminth control for many years. Discussion continues on the optimal method of MDA for this purpose. In some cases, such as where high rates of strongyloidiasis or onchocerciasis are present, the addition of other drugs may be warranted. Further consideration of new therapies, combination therapies, the reconsideration of use of the use of ‘old’ anti-helminthic therapies have all been postulated as mechanisms by which to improve absolute cure rates in MDA programs and to reduce the possible development of antihelminthic resistance⁹. Ways to improve MDA participation, as well as paediatric formulations of praziquantel for schistosomiasis prevention in preschool children may also be added to this list. The current WHO protocols for MDA provide an important baseline guide to those undertaking MDA for helminth control in endemic areas.