Polymerase Chain Reaction Monitoring of Transmission of Onchocerca Volvulus in Two Endemic States in Mexico

Abstract

To investigate the impact of mass ivermectin treatments in Mexico on Onchocerca volvulus transmission, entomologic surveys were carried out in the two endemic states of Oaxaca and Chiapas. The data suggest that substantial progress towards the goal of elimination has been made. A comparison pre- and post-ivermectin data from a community in Southern Chiapas showed a 97% decrease in seasonal transmission potential, but some level of polymerase chain reaction positivity was still detectable. In other communities from northern Chiapas and Oaxaca where there are no baseline data, there was an absence or near absence of infective flies. Residual transmission was not evenly distributed because differences were seen in the infection and infective rates from different catch points. These findings suggest that while substantial progress towards elimination has been made in Mexico, it may be necessary to modify ivermectin distribution strategies to eliminate transmission in areas where transmission persists.

Interruption of Transmission of Onchocerca volvulus in the Oaxaca Focus, Mexico

“…6 The separated head and body pools were tested for O. volvulus parasites by using a PCR assay specific for O. volvulus . Details of protocols for genomic DNA purification, primer sequences, PCR conditions, and detection of PCR products by enzyme-linked immunosorbent assay (ELISA) have been published elsewhere.…”

Polymerase Chain Reaction Pool Screening Used To Compare Prevalence of Infective Black Flies in Two Onchocerciasis Foci in Northern Sudan

“…Black flies were obtained and head pools of ≤ 100 heads were processed for O. volvulus -specific the O-150 polymerase chain reaction (PCR) and PCR-based enzyme-linked immunosorbent assay (ELISA) as reported. [15][16][17] A sample was considered putatively positive if it had an ELISA score at or above the cutoff (i.e., the mean of 10 internal negative controls plus 3 SD). Samples positive after a second independent PCR and ELISA were reported as confirmed positive.…”

Lack of Active Onchocerca volvulus Transmission in the Northern Chiapas Focus of Mexico

“…[2][3][4][5] However, entomologic and serologic studies carried out in 2001 and 2005 indicated that autochthonous transmission of O. volvulus might be occurring in the northern Chiapas focus, albeit at a low level. [6][7][8] The conclusion that transmission of O. volvulus is rare or non-existent in northern Chiapas is supported by the clinical incidence reports from the local health officials. The last five new clinical cases (i.e., individuals diagnosed positive for nodules or skin microfilariae [mf] for the first time) were reported in 1996 ( Figure 2 ), when four individuals who had traveled outside of northern Chiapas were found to contain mf in skin snips.…”

“…Entomologic study. Black flies were collected by using standard procedures 6,11 from February to May 2005 coinciding with the peak O. volvulus transmission season. 12 The collections were carried out during the first 50 minutes of Black flies were collected before they began feeding.…”