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Nodding Syndrome

Close to Solving the Mystery

Bhwana, Dan MD; Mmbando, Bruno PhD; Hotterbeekx, An PhD; Colebunders, Robert MD, PhD

The Pediatric Infectious Disease Journal: November 2019 - Volume 38 - Issue 11 - p e313
doi: 10.1097/INF.0000000000002442
Letters to the Editor
Free

Tanga Research Centre, National Institute for Medical Research, Tanga, Tanzania

Tanga Research Centre, National Institute for Medical Research, Tanga, Tanzania

Global Health Institute, University of Antwerp, Antwerp, Belgium

Global Health Institute, University of Antwerp, Antwerp, Belgium.

The authors have no funding or conflicts of interest to disclose.

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To the Editors:

We read with interest the review paper by G Abd-Elfarag and B Hensbroek on nodding syndrome (NS).1 We would like to complement their findings by highlighting some recent research updates which are not cited in the paper, but are important to solve the mystery.

The authors mention that NS poses a major public health problem in parts of Uganda, South Sudan and Tanzania. It is, however, important to note that new cases of NS have stopped to appear in northern Uganda since bi-annual mass ivermectin distribution and larviciding of rivers were successfully implemented.2 This is in contrast to onchocerciasis-endemic regions in South Sudan, where the onchocerciasis elimination efforts have been interrupted for many years and where children continue to develop NS.3

The authors mention that the current burden of NS in Tanzania is not known. Observations from community-based studies clearly reveal that the burden of disease caused by NS in Tanzania is much lower than in northern Uganda and South Sudan. We recently performed a house-to-house epilepsy survey in 2 rural and 2 sub-urban villages in the Mahenge area in the Ulanga district of Tanzania.4 The prevalence of epilepsy in the 2 rural villages was 3.5% compared with 1.5% in the sub-urban villages (P < 0.001). Twelve cases of NS (0.49%) were identified among 2499 inhabitants in the rural villages while only 1 case of NS (0.06%) was identified among 1738 inhabitants in the sub-urban villages.4 These differences in epilepsy prevalence are most likely explained by the high degree of Onchocerca volvulus transmission in the rural villages, which are located close to blackfly (the vector transmitting onchocerciasis) breeding sites. This hypothesis is backed by the higher prevalence of O. volvulus (OV16) antibodies among children 6–10 years old in the rural villages compared with the sub-urban villages, respectively, 42.6% versus 4.7% (P < 0.001).4

One of the arguments cited by the authors against an etiologic link between Onchocerciasis and NS is that NS has only been observed in onchocerciasis-endemic areas in East Africa. This argument can no longer be used as NS and NS-like manifestations such as the Nakalanga syndrome have also be reported in West- and Central Africa.2

In onchocerciasis-endemic areas with high O. volvulus transmission, NS cases and other forms of epilepsy occur clustered in villages and families located close to blackfly-breeding sites,5 suggesting NS is most likely part of an epilepsy spectrum triggered directly or indirectly by O. volvulus infection.5 Therefore, NS is preventable by strengthening onchocerciasis elimination efforts. In the meantime, research needs to continue to identify the pathophysiologic mechanism causing NS.

Dan Bhwana, MD

Tanga Research Centre, National Institute for Medical Research, Tanga, Tanzania

Bruno Mmbando, PhD

Tanga Research Centre, National Institute for Medical Research, Tanga, Tanzania

An Hotterbeekx, PhD

Global Health Institute, University of Antwerp, Antwerp, Belgium

Robert Colebunders, MD, PhD

Global Health Institute, University of Antwerp, Antwerp, Belgium.

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REFERENCES

1. Abd-Elfarag G, van Hensbroek MB. Nodding syndrome: the unresolved mystery of a pediatric disease in sub-saharan Africa. Pediatr Infect Dis J. 2019;386S suppl 1S67–S71.
2. Colebunders R, Nelson Siewe FJ, Hotterbeekx A. Onchocerciasis-associated epilepsy, an additional reason for strengthening onchocerciasis elimination programs. Trends Parasitol. 2018;34:208–216.
3. Colebunders R, Carter J, Olore PC, et al. High prevalence of onchocerciasis-associated epilepsy in villages in Maridi County, Republic of South Sudan: a community-based survey. Seizures. 2018;63:93–101.
4. Mmbando BP, Suykerbuyk P, Mnacho M, et al. High prevalence of epilepsy in two rural onchocerciasis endemic villages in the Mahenge area, Tanzania, after 20 years of community directed treatment with ivermectin. Infect Dis Poverty. 2018;7:64.
5. Colebunders R, Abd-Elfarag G, Carter JY, et al. Clinical characteristics of onchocerciasis-associated epilepsy in villages in Maridi County, Republic of South Sudan. Seizure. 2018;62:108–115.
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