Treating neglected tropical diseases
The name neglected tropical diseases (NTDs) covers a range of diseases that cause disability, early death, and slowed physical and mental development. The first two in entries Table 1 are diseases that cause blindness. These diseases of neglected and impoverished peoples maintain a cycle of poverty and delayed development of the populations affected. The diseases themselves have been neglected in the push to control malaria, TB and AIDS.
The NTDs fall into two main groups. The first group, which we will deal with here, are those for which we have tools (easy community diagnosis or mapping, as well as the drugs or medicines). These NTDs can be treated – where safe to do so – in large populations of patients using a mass drug administration (MDA) strategy. Dosages are standardised, and a dose pole can be used to measure the height of a person in order to calculate the dose required.
The second group of diseases, which we will not discuss here, require either more difficult or costly diagnosis and the people affected often need individualised treatment.
Treatment with drugs is important. Repeated annual or semi-annual drug distribution can lower the prevalence of a disease and, in some settings, eliminate transmission. However, in order to maintain these gains, more intensive efforts need to be made to provide safe water, sanitation, and hygiene. Specific measures are also required in trachoma and lymphatic filariasis (LF) to address the symptoms and consequences of these diseases, e.g. trichiasis surgery to correct in-turned eyelashes and prevent corneal scarring in people affected by trachoma and hydrocoele surgery for male genital deformity due to LF. The existence of an MDA programme is not a reason to ignore these other measures.
Table 1. Current treatment guidelines for the five neglected tropical diseases for which mass drug administration is possible
|Disease||Drugs and Dosages||Threshold for implementation||Frequency of Intervention|
|Trachoma||Azithromycin 20 mg/kg, with a maximum dose of 1 g in adults. Use a dose pole to determine dose. Offer tetracycline eye ointment for children <6 months||
||Annual. Must be part of an integrated SAFE strategy (Surgery, Antibiotics, Facial cleanliness, Environmental improvement)|
|Onchocerciasis||Ivermectin 150 μ/Kg using dose pole for everyone >5 years (or >90 cm), except the chronically ill and pregnant and lactating women during the first week after delivery||For control: nodule prevalence ≥20% or skin microfilaria ≥40%
For elimination: under discussion. APOC is using nodule prevalence ≥5%
|Annual or twice yearly. (Exceptionally quarterly)|
|Lymphatic filariasis||Albendazole 400 mg for children aged >2 years plus diethylcarbamazine (DEC) 6 mg/kg in countries where onchocerciasis is not co-endemic, or ivermectin 150 μ/Kg in countries where onchocerciasis is endemic||Prevalence of ≥1%||Annual. Treatment must be combined with limb care of patients with elephantiasis or hydrocoele surgery|
|Soil-transmitted helminths (STH) (Ascaris, hookworms and Trichuris)||Albendazole 400 mg for children above 2 years, or mebendazole 500 mg||Prevalence ≥50%:treat school-aged children, and adults at high risk, twice yearly
Prevalence >20% to <50%: treat school-aged children once per year.
Prevalence <20%: individualised treatment. Pre-school children and women of childbearing age should also be treated (as part of maternal and child health programmes)
|Annual or twice yearly depending on prevalence. Water and sanitation strategies must be implemented|
|Schistosomiasis||Praziquantel 40 mg/kg (using dose pole) for children over 4 years (or 94 cms)||Prevalence ≥50%: treat all school-aged children. Adults at high risk may also be treated
Prevalence >10% to <50%: treat children once every two years
Prevalence <10%: individualised treatment
|Annual treatment Treatment holidays can be given if prevalence drops. Water and sanitation strategies must be implemented|
Adapted from: ‘Preventive Chemotherapy in Human Helminthiasis.’1 This book should be consulted before commencing any MDA, however, the situation is continually changing as new research leads to new strategies.
Many of the drugs used in MDA can be given together, at one time, so making distribution much more efficient. In Africa, ivermectin should be given with albendazole to eliminate LF. Both these drugs have an effect on soil-transmitted helminths (STHs), and ivermectin also kills ectoparasites such as scabies. Where populations are treated for LF, onchocerciasis and STHs will be treated at the same time. Praziquantel can also be given with ivermectin and albendazole. At the present time, research is ongoing into co-administration of azithromycin with ivermectin and albendazole, but for the moment there should be an interval of 2 weeks between the administration of azithromycin and the other drugs.
Drugs used in MDA have certain adverse effects and there are several precautions to be taken before using them. Where there is a high worm load in onchocerciasis, there will be symptoms of pain, fever, itching and swelling after treatment, depending on the number of parasites present. These symptoms last for up to 2 days and need symptomatic treatment. Second and subsequent rounds of treatments have far fewer side effects and after three annual treatments there are usually no further adverse effects.
In forested areas of Africa where the parasite Loa loa (tropical eye worm) is present, ivermectin should only be given following strict guidelines, otherwise the effects can be severe and sometimes life threatening. Praziquantel should not be given on an empty stomach and will provoke nausea and vomiting in some children, particularly if they have not eaten. Azithromycin also can cause some minor stomach problems. Apart from the Loa loa situation, the adverse effects are minor and are not contra-indications to treatment; however, in people who suffer with many different parasites, drugs should not all be given together at the first administration.