Loiasis

Public Health and Prevention

RAPLOA and Onchocerciasis

The severe side effects of Ivermectin on individuals being treated for onchocerciasis that are also infected with Loa loa is of great concern, especially in the mass treatment programs in Africa. A WHO/UNDP/World Bank/African Program for Onchocerciasis Control study was carried out in 2001 in Cameroon and Nigeria to develop and evaluate a rapid assessment procedure for loiasis endemicity (RAPLOA) and the risk of these side effects in populations being treated for onchocerciasis. While the risk of side effects increases greatly with increasing intensity of loiasis infection, as measured by microfilaria/mL of blood, it is not feasible to determine this for every person being treated in Ivermectin mass treatment programs, as blood smears are time consuming

In this study interviews were conducted that asked individuals about their knowledge of other people who had experience with eye worms, Calabar swellings, and if they themselves had these symptoms, what they called the symptoms locally, and how long they lasted. Thick blood films from each of these individuals were also prepared. The study made the important linkage between prevalence and intensity of loiasis, which means that a higher microfilaremic load is likely to be indicated by a widespread prevalence in the area. The results were consistent with another study that asserted that a 20% prevalence rate of loiasis indicated a 5% prevalence of high microfilaric loads (>8,000 mf/ml) and a 2% prevalence of very high loads (>30,000 mf/ml).

The interviews were scored according to answers and scores of 40% or greater were indicative of a high risk of adverse reaction to Ivermectin treatment. By far the best indicator was based on the definition of the eye worm, and in all highly endemic areas the local population had a specific name for it, which was not the case throughout the villages studies. For more information on this study, please go to http://www.who.int/tdr/publications/publications/pdf/raploa.pdf.

Prophylaxis

DEC can be used as in prophylaxis for uninfected people who are entering endemic areas for extended stays, with an adult dosage of 300 mg each week. The most important precaution in endemic areas is to avoid the bite of the vector with insect repellent and long sleeved shirts and pants. Heavy clothing offers better protection than light clothing as tabanids can bite through some clothing.

Control of the vector is not an easy option in this case because of the widespread distribution and biting habits of the tabanids. They do not usually bite indoors either, so indoor spraying of insecticide is not an effective countermeasure.

Monkeys and American Deerflies

Recent public health concerns center around the fact that some African monkeys can become infected with Loa loa, but the possibility of transmission to humans is not proven. Also, the monkey strain has a nocturnal periodicity and is carried by a different species of Chrysops than the human strains.

Also, it was reported that a species of American deerfly, Chrysops atlanticus, can harbor Loa loa and even transmit it to monkeys, so a viable vector may exist stateside for this parasite.

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