Onchocerca volvulus: striking decrease in transmission in the Vina valley (Cameroon) after eight annual large scale ivermectin treatments

Abstract

The impact of repeated ivermectin treatments on the transmission of Onchocerca volvulus was evaluated in the Vina valley, northern Cameroon, by comparing the prevalence and intensity of infection observed in untreated 5-7 years old children living in the treated communities before and after 7-8 successive annual rounds of ivermectin treatment of the general population of those communities. The villages studied were Ngoumi and Babidan, where the initial community microfilarial loads (CMFL) were 83.7 and 216.4 microfilariae per skin snip, respectively. In 1995, after 8 annual treatments, the prevalence and intensity in Ngoumi had decreased by more than 90%, compared with the pretreatment values, and the prevalence continued to decrease between 1992 and 1995. In Babidan, after 7 annual treatments, the prevalence and intensity had also decreased significantly, but less than in Ngoumi. The study demonstrated that repeated treatments brought about a notable reduction in the transmission of O. volvulus in the Vina valley, despite unfavourable factors such as mean drug coverages below 60% and the good vectorial competence of Simulium damnosum s.s. and S. sirbanum.

Seventeen Years of Annual Distribution of Ivermectin Has Not Interrupted Onchocerciasis Transmission in North Region, Cameroon

“…However, previous work in Toubouro showed mf rates of > 90% in two of six villages (Babidan and Koubao) that we reexamined in 2009. 28 This result is higher than the baseline recorded by Renz for Tchollire (39%) or Rey-Bouba (58%; unpublished data). Baseline ATP ( Figure 3 ) in Toubouro was over seven times the baseline ATP in Tchollire.…”

“…The force of infection is a combination of high vector density and human hyperendemicity, and these observations suggest that the initial force of transmission may have been highest in Toubouro. 8,28 However, the standard measure of intensity of infection (which is related to force of infection) is the community mf load (CMFL); this measure could not be calculated in the present study, because mf counts were not done and weights of the snips were not known. Corneoscleral punches, which have traditionally been used to provide a consistent skin snip sample (mf/snip) from which CMFL can also be calculated, were not used in this study.…”

Pool screen polymerase chain reaction for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control.

“…19,20 A similar situation is also likely to arise in areas subject to long-term ivermectin distribution. 8 The use of the PCR pool screening technique will make it possible to determine the level of transmission in a given area with a limited investment of human and material resources. This technique may thus be a valuable tool for the surveillance activities to be conducted in the OCP area following the cessation of active vector control in 2002.…”

“…This is true both for programs relying on vector control 7 and for those using mass ivermectin distribution. 8 Thus, the classic dissection method to determine the prevalence of infection becomes progressively less efficient in areas where control has been successful.…”

Nodding syndrome in Mundri county, South Sudan: Environmental, nutritional and infectious factors

“…[96][97] Consequently single treatments with ivermectin do not change the infection status of treated subjects, and the effect of ivermectin mass treatment on infection prevalence is primarily due to reduction in transmission. [98][99][100][101][102][103] Between 1987 and 2011, the Mectizan Donation programme approved 139,265,010 ivermectin treatments for Africa. 104 Adverse reactions to ivermectin treatment of O. volvulus infection constitute the body's reaction to the microfilaria killed and include primarily itching, rash, gland pain and tenderness, joint and muscle pain, fever and headache, pulse and blood pressure changes, all of which disappear within a few days.…”