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Contribution of migrant coffee labourers infected with Onchocerca volvulus to the maintenance of the microfilarial reservoir in an ivermectin-treated area of Mexico.

Rodríguez-Pérez MA, Cabrera AS, Ortega CL, Basáñez MG, Davies JB - Filaria J (2007)

Bottom Line: The proportion of infected Simulium ochraceum s.l. parous flies was significantly lower in locality I than in locality II, and significantly higher during the stay of the migrants than before their arrival or after their departure.The presence of significant numbers of untreated and potentially infected migrants may contribute to ongoing transmission, and their incorporation into ivermectin programmes should be beneficial for the attainment of the elimination goals of the regional initiative.However, the possibility that the results also reflect transmission patterns for the area cannot be excluded and these should be analyzed further.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centro de Biotecnología Genómica, Instituto Politécnico Nacional, Blvd, del Maestro esquina Elías Piña, Col, Narciso Mendoza, 88710, Reynosa, Tamaulipas, México. mrodriguez@ipn.mx

ABSTRACT

Background: Since 1991, in Mexico, ivermectin has been administered twice a year to all residents in the onchocerciasis endemic foci which are mainly located in the coffee growing areas. However, the presence of a potentially infected itinerant seasonal labour force which is not treated regularly could jeopardise the attainment of the 85% coverage which is the present target for elimination of the disease.

Methods: The prevalence and intensity of Onchocerca volvulus microfilariae (mf), as well as their transmission from humans to vectors, were assessed during the coffee planting-clearing and harvesting seasons of 1997-1998, and 1998-1999 in two localities (I and II) of Southern Chiapas, Mexico, which regularly receive an influx of untreated migrant coffee labourers.

Results: Localities I and II had, respectively, an average of 391 (+/- 32) and 358 (+/- 14) resident inhabitants, and 70 (+/- 52) and 498 (+/- 289) temporary labourers. The ratio of migrants to residents ranged from 0.1:1 in locality I to 2.4:1 in locality II. The proportion of infected Simulium ochraceum s.l. parous flies was significantly lower in locality I than in locality II, and significantly higher during the stay of the migrants than before their arrival or after their departure. Parity and infection were higher in May-July than in November-February (in contrast with the latter being typically considered as the peak onchocerciasis transmission season by S. ochraceum s.l.).

Conclusion: The presence of significant numbers of untreated and potentially infected migrants may contribute to ongoing transmission, and their incorporation into ivermectin programmes should be beneficial for the attainment of the elimination goals of the regional initiative. However, the possibility that the results also reflect transmission patterns for the area cannot be excluded and these should be analyzed further.

No MeSH data available.


Related in: MedlinePlus

Map of the Mexican-Guatemalan border area showing the geographical location of the three villages and four coffee fincas studied within the southern Chiapas focus endemic for human onchocerciasis, Mexico (indicated by A in the inset).
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Figure 1: Map of the Mexican-Guatemalan border area showing the geographical location of the three villages and four coffee fincas studied within the southern Chiapas focus endemic for human onchocerciasis, Mexico (indicated by A in the inset).

Mentions: In 1996, and before the present study was conducted, it had been assumed that the impact on transmission would be more evident in villages with high coverage of and compliance to ivermectin and nodulectomy; therefore three villages with such characteristics were selected for the study described here, namely: Las Golondrinas (92°39'17" W, 15°26'06" N, 920 m above sea level (masl)), Rosario Zacatonal (92°37'47" W, 15°27'25" N, 791 masl), and Nueva América (92°26'38" W, 15°17'08" N, 880 masl), which, prior to the introduction of ivermectin, had microfilarial prevalences of 69%, 79%, and 46% respectively [22]. Las Golondrinas and Rosario Zacatonal are 7.0 km apart from each other and a coffee finca (Palestina) is located between 2.5 and 3.0 km from each village respectively; they all constitute locality I. The village of Nueva América is surrounded by three coffee fincas, namely, La Victoria, La Fortuna, and Santa Fe, which are located at a distance between 2 and 5 km from the village; they all constitute locality II. The study area is depicted in Fig. 1. The closest simuliid breeding sites were located approximately at 6.0 km from Las Golondrinas, 1.0 km from Rosario Zacatonal, 2.5 km from Palestina, 2.0 km from Nueva América, 2.0 km from La Victoria, 1.0 km from La Fortuna, and 0.5 km from Santa Fe, i.e. within the flight range of S. ochraceum s.l. [23,24]. Treatment is typically administered to the eligible resident populations of each village in January and June of each year. In 1996, the average ivermectin treatment coverage among the total population had been of about 80%. However, for the purposes of this study, the residents were not treated as usual in January and June, but immediately after parasitological examination, which took place in May and November to coincide with the commencement of each of the annual coffee seasons (see below). A census of each community was conducted [10,16] at the start of each survey in 1997–1998 and 1998–1999, and eligible residents were treated just after the parasitological examination was completed.


Contribution of migrant coffee labourers infected with Onchocerca volvulus to the maintenance of the microfilarial reservoir in an ivermectin-treated area of Mexico.

Rodríguez-Pérez MA, Cabrera AS, Ortega CL, Basáñez MG, Davies JB - Filaria J (2007)

Map of the Mexican-Guatemalan border area showing the geographical location of the three villages and four coffee fincas studied within the southern Chiapas focus endemic for human onchocerciasis, Mexico (indicated by A in the inset).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2238739&req=5

Figure 1: Map of the Mexican-Guatemalan border area showing the geographical location of the three villages and four coffee fincas studied within the southern Chiapas focus endemic for human onchocerciasis, Mexico (indicated by A in the inset).
Mentions: In 1996, and before the present study was conducted, it had been assumed that the impact on transmission would be more evident in villages with high coverage of and compliance to ivermectin and nodulectomy; therefore three villages with such characteristics were selected for the study described here, namely: Las Golondrinas (92°39'17" W, 15°26'06" N, 920 m above sea level (masl)), Rosario Zacatonal (92°37'47" W, 15°27'25" N, 791 masl), and Nueva América (92°26'38" W, 15°17'08" N, 880 masl), which, prior to the introduction of ivermectin, had microfilarial prevalences of 69%, 79%, and 46% respectively [22]. Las Golondrinas and Rosario Zacatonal are 7.0 km apart from each other and a coffee finca (Palestina) is located between 2.5 and 3.0 km from each village respectively; they all constitute locality I. The village of Nueva América is surrounded by three coffee fincas, namely, La Victoria, La Fortuna, and Santa Fe, which are located at a distance between 2 and 5 km from the village; they all constitute locality II. The study area is depicted in Fig. 1. The closest simuliid breeding sites were located approximately at 6.0 km from Las Golondrinas, 1.0 km from Rosario Zacatonal, 2.5 km from Palestina, 2.0 km from Nueva América, 2.0 km from La Victoria, 1.0 km from La Fortuna, and 0.5 km from Santa Fe, i.e. within the flight range of S. ochraceum s.l. [23,24]. Treatment is typically administered to the eligible resident populations of each village in January and June of each year. In 1996, the average ivermectin treatment coverage among the total population had been of about 80%. However, for the purposes of this study, the residents were not treated as usual in January and June, but immediately after parasitological examination, which took place in May and November to coincide with the commencement of each of the annual coffee seasons (see below). A census of each community was conducted [10,16] at the start of each survey in 1997–1998 and 1998–1999, and eligible residents were treated just after the parasitological examination was completed.

Bottom Line: The proportion of infected Simulium ochraceum s.l. parous flies was significantly lower in locality I than in locality II, and significantly higher during the stay of the migrants than before their arrival or after their departure.The presence of significant numbers of untreated and potentially infected migrants may contribute to ongoing transmission, and their incorporation into ivermectin programmes should be beneficial for the attainment of the elimination goals of the regional initiative.However, the possibility that the results also reflect transmission patterns for the area cannot be excluded and these should be analyzed further.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centro de Biotecnología Genómica, Instituto Politécnico Nacional, Blvd, del Maestro esquina Elías Piña, Col, Narciso Mendoza, 88710, Reynosa, Tamaulipas, México. mrodriguez@ipn.mx

ABSTRACT

Background: Since 1991, in Mexico, ivermectin has been administered twice a year to all residents in the onchocerciasis endemic foci which are mainly located in the coffee growing areas. However, the presence of a potentially infected itinerant seasonal labour force which is not treated regularly could jeopardise the attainment of the 85% coverage which is the present target for elimination of the disease.

Methods: The prevalence and intensity of Onchocerca volvulus microfilariae (mf), as well as their transmission from humans to vectors, were assessed during the coffee planting-clearing and harvesting seasons of 1997-1998, and 1998-1999 in two localities (I and II) of Southern Chiapas, Mexico, which regularly receive an influx of untreated migrant coffee labourers.

Results: Localities I and II had, respectively, an average of 391 (+/- 32) and 358 (+/- 14) resident inhabitants, and 70 (+/- 52) and 498 (+/- 289) temporary labourers. The ratio of migrants to residents ranged from 0.1:1 in locality I to 2.4:1 in locality II. The proportion of infected Simulium ochraceum s.l. parous flies was significantly lower in locality I than in locality II, and significantly higher during the stay of the migrants than before their arrival or after their departure. Parity and infection were higher in May-July than in November-February (in contrast with the latter being typically considered as the peak onchocerciasis transmission season by S. ochraceum s.l.).

Conclusion: The presence of significant numbers of untreated and potentially infected migrants may contribute to ongoing transmission, and their incorporation into ivermectin programmes should be beneficial for the attainment of the elimination goals of the regional initiative. However, the possibility that the results also reflect transmission patterns for the area cannot be excluded and these should be analyzed further.

No MeSH data available.


Related in: MedlinePlus