Letter to the editor
The disappearance of onchocerciasis without intervention in Tigray Region in Northwest Ethiopia Moses N. Katabarwa1, Tekola Endeshaw2, Aseged Taye2, Zerihun Tadesse2, Richards O. Frank1 1
The Carter Center, Atlanta, GA, USA, 2The Carter Center-Addis, Ababa, Ethiopia
Dear Editor, We would like to inform you that onchocerciasis in Tigray Region in Northwest Ethiopia disappeared without any interventions. Zein et al.1 in a study conducted in 1981 showed that onchocerciasis was endemic in the villages of Baaker, Bewal, Heligen, Umhager, and Humera town of Kafta Humera District in Mi’irabawi Zone of Tigray Region, northwestern Ethiopia. The study assessed 1050 adults and 320 children for subcutaneous onchocercomas (nodules) and skin microfilaria. Among adults, nodule prevalence was 2.0% and microfilaria prevalence, 24.6%. In children, no nodules were observed, and microfilaria prevalence was 2.8%. Interventions against onchocerciasis were never undertaken. We repeated a similar survey in October 2009 to determine if mass drug administration (MDA) for onchocerciasis was needed. We discovered upon visiting the area that most of the population in the district had left as a result of local civil conflict, and the land converted from small holder farming into large scale agricultural enterprises supported by seasonal migrant labour that came from non onchocerciasis endemic areas in Ethiopia. However, all the villages visited by Zein et al.,1 with exception of Umhager (now in Eritrea), were still present and we were able to find persons who were original residents for our repeat survey. A total of 678 adults (resident in the village for over 10 years, and over 20 years of age) and 134 resident children (3–10 years of age) were assessed for microfilaria and nodules using standard techniques.2 We also performed an entomological spot check in the River Takeze, previously known as the main black fly breeding site in October 2009, using techniques we employed previously in Uganda for this purpose.3 Correspondence to: M. N. Katabarwa, The Carter Center, Atlanta, USA. Email: [email protected]
ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2047772414Z.000000000198
Compared to the baseline survey conducted 28 years previously, nodule prevalence among adults had decreased from 2.0% to 1%, and microfilaria rate from 24.6% to 0% (P , 0.0001). In children, no nodules were observed, and microfilaria prevalence was 0% (compared to 2.8% in 1981, P , 0.05). Rapid prospection of the River Takeze did not yield any adult black flies or their aquatic stages, and adult residents who had been living in the proximity of the River Takeze all their lives recounted that they had not suffered from black fly biting for many years. Absence of infection in adults and children indicated that onchocerciasis transmission had disappeared without MDA or entomological intervention. The disappearance of onchocerciasis from this area may have been a result of emigration of the majority of the indigenous population, and/or environmental change resulting from large scale commercial farming techniques that may have had a negative impact on black fly breeding sites. This may have been compounded by the influx of seasonal migratory labour force that may have reduced the proportion of the human population infected below that needed to maintain onchocerciasis transmission. One or more of these changes have resulted in the disappearance of the disease. To our knowledge, this is the first documented evidence of onchocerciasis disappearance due purely to population movement and/or drastic change in land use without mass drug administration or vector control measures.
References 1 Zein ZA. The epidemiology of onchocerciasis in North western Ethiopia. Trop Geogr Med. 1985;38:33–7. 2 Schulz-Key H. A simple technique to assess the total number of Onchocerca volvulus microfilariae in skin snips. Tropenmed Parasitol. 1978;29:51–4. 3 Katabarwa NM, Walsh F, Habomugisha P, Lakwo T, Agunyo S, Oguttu D, et al. Transmission of onchocerciasis in Wadelai focus of northwestern Uganda has been interrupted and the disease eliminated. J Parasitol Res. 2012;2012:748540.
Pathogens and Global Health
2014
VOL.
108
NO.
3
123
The disappearance of onchocerciasis without intervention in Tigray Region in Northwest Ethiopia Moses N. Katabarwa1, Tekola Endeshaw2, Aseged Taye2, Zerihun Tadesse2, Richards O. Frank1 1
The Carter Center, Atlanta, GA, USA, 2The Carter Center-Addis, Ababa, Ethiopia
Dear Editor, We would like to inform you that onchocerciasis in Tigray Region in Northwest Ethiopia disappeared without any interventions. Zein et al.1 in a study conducted in 1981 showed that onchocerciasis was endemic in the villages of Baaker, Bewal, Heligen, Umhager, and Humera town of Kafta Humera District in Mi’irabawi Zone of Tigray Region, northwestern Ethiopia. The study assessed 1050 adults and 320 children for subcutaneous onchocercomas (nodules) and skin microfilaria. Among adults, nodule prevalence was 2.0% and microfilaria prevalence, 24.6%. In children, no nodules were observed, and microfilaria prevalence was 2.8%. Interventions against onchocerciasis were never undertaken. We repeated a similar survey in October 2009 to determine if mass drug administration (MDA) for onchocerciasis was needed. We discovered upon visiting the area that most of the population in the district had left as a result of local civil conflict, and the land converted from small holder farming into large scale agricultural enterprises supported by seasonal migrant labour that came from non onchocerciasis endemic areas in Ethiopia. However, all the villages visited by Zein et al.,1 with exception of Umhager (now in Eritrea), were still present and we were able to find persons who were original residents for our repeat survey. A total of 678 adults (resident in the village for over 10 years, and over 20 years of age) and 134 resident children (3–10 years of age) were assessed for microfilaria and nodules using standard techniques.2 We also performed an entomological spot check in the River Takeze, previously known as the main black fly breeding site in October 2009, using techniques we employed previously in Uganda for this purpose.3 Correspondence to: M. N. Katabarwa, The Carter Center, Atlanta, USA. Email: [email protected]
ß W. S. Maney & Son Ltd 2014 DOI 10.1179/2047772414Z.000000000198
Compared to the baseline survey conducted 28 years previously, nodule prevalence among adults had decreased from 2.0% to 1%, and microfilaria rate from 24.6% to 0% (P , 0.0001). In children, no nodules were observed, and microfilaria prevalence was 0% (compared to 2.8% in 1981, P , 0.05). Rapid prospection of the River Takeze did not yield any adult black flies or their aquatic stages, and adult residents who had been living in the proximity of the River Takeze all their lives recounted that they had not suffered from black fly biting for many years. Absence of infection in adults and children indicated that onchocerciasis transmission had disappeared without MDA or entomological intervention. The disappearance of onchocerciasis from this area may have been a result of emigration of the majority of the indigenous population, and/or environmental change resulting from large scale commercial farming techniques that may have had a negative impact on black fly breeding sites. This may have been compounded by the influx of seasonal migratory labour force that may have reduced the proportion of the human population infected below that needed to maintain onchocerciasis transmission. One or more of these changes have resulted in the disappearance of the disease. To our knowledge, this is the first documented evidence of onchocerciasis disappearance due purely to population movement and/or drastic change in land use without mass drug administration or vector control measures.
References 1 Zein ZA. The epidemiology of onchocerciasis in North western Ethiopia. Trop Geogr Med. 1985;38:33–7. 2 Schulz-Key H. A simple technique to assess the total number of Onchocerca volvulus microfilariae in skin snips. Tropenmed Parasitol. 1978;29:51–4. 3 Katabarwa NM, Walsh F, Habomugisha P, Lakwo T, Agunyo S, Oguttu D, et al. Transmission of onchocerciasis in Wadelai focus of northwestern Uganda has been interrupted and the disease eliminated. J Parasitol Res. 2012;2012:748540.
Pathogens and Global Health
2014
VOL.
108
NO.
3
123
