Identifying suitable methods for evaluating the sterilizing effects of pyriproxyfen on adult malaria vectors: a comparison of the oviposition and ovary dissection methods

Abstract Background Nets containing pyriproxyfen, an insect growth regulator that sterilizes adult mosquitoes, have become available for malaria control. Suitable methods for investigating vector susceptibility to pyriproxyfen and evaluating its efficacy on nets need to be identified. The sterilizing effects of pyriproxyfen on adult malaria vectors can be assessed by measuring oviposition or by dissecting mosquito ovaries to determine damage by pyriproxyfen (ovary dissection). Method Laboratory bioassays were performed to compare the oviposition and ovary dissection methods for monitoring susceptibility to pyriproxyfen in wild malaria vectors using WHO bottle bioassays and for evaluating its efficacy on nets in cone bioassays. Blood-fed mosquitoes of susceptible and pyrethroid-resistant strains of Anopheles gambiae sensu lato were exposed to pyriproxyfen-treated bottles (100 μg and 200 μg) and to unwashed and washed pieces of a pyriproxyfen long-lasting net in cone bioassays. Survivors were assessed for the sterilizing effects of pyriproxyfen using both methods. The methods were compared in terms of their reliability, sensitivity, specificity, resources (cost and time) required and perceived difficulties by trained laboratory technicians. Results The total number of An. gambiae s.l. mosquitoes assessed for the sterilizing effects of pyriproxyfen were 1745 for the oviposition method and 1698 for the ovary dissection method. Fertility rates of control unexposed mosquitoes were significantly higher with ovary dissection compared to oviposition in both bottle bioassays (99–100% vs. 34–59%, P  99%), but not with the oviposition method (69%). Both methods showed similar levels of sensitivity (89–98% vs. 89–100%). Specificity was substantially higher with ovary dissection compared to the oviposition method in both bottle bioassays (99–100% vs. 34–48%) and cone tests (100% vs.18–76%). Ovary dissection was also more sensitive for detecting the residual activity of pyriproxyfen in a washed net compared to oviposition. The oviposition method though cheaper, was less reliable and more time-consuming. Laboratory technicians preferred ovary dissection mostly due to its reliability. Conclusion The ovary dissection method was more accurate, more reliable and more efficient compared to the oviposition method for evaluating the sterilizing effects of pyriproxyfen on adult malaria vectors in susceptibility bioassays and for evaluating the efficacy of pyriproxyfen-treated nets

Enteric pathogen detection among children discharged from outpatient treatment for severe acute malnutrition and associations with subsequent relapse in South Sudan

Severe acute malnutrition (SAM) affects millions of children each year, putting them at increased risk of death and disease. Many children relapse to acute malnutrition (AM) or SAM following community-based management of acute malnutrition (CMAM) programmes. Enteric infection is hypothesized to be a risk factor for relapse. We collected rectal swabs from children recently recovered from uncomplicated SAM in South Sudan and tested them for a suite of enteric pathogens using a TaqMan Array Card. We estimated enteric pathogen prevalence and examined associations between pathogen detection and risk of relapse to AM and SAM within three and six months of recovery. One or more enteric pathogen was detected in 82% of children (389/476). Bacterial and protozoan pathogens were the most frequently detected pathogen types, with each detected in 57% of children, followed by enteric viruses (10%) and helminths (4.4%). Detection of one or more enteric pathogen, protozoan pathogen, or viral pathogen was not associated with relapse to AM or SAM at either time point. Detection ≥1 helminth was associated with increased risk of relapse to SAM, and ≥1 bacterial pathogen was associated with decreased risk of relapse to AM. Both enterotoxigenic E. coli and enteroaggregative E. coli were associated with decreased risk of relapse to SAM and/or AM at three- or six-months post-recovery. Shigella was the only individual pathogen associated with increased risk of relapse to AM and SAM. In this setting, most children suffering from SAM were exposed to enteric pathogens during treatment. However, we found no consistent relationship between pathogen detection at treatment discharge and risk of relapse to AM or SAM within three or six months of recovery. Despite this, limiting pathogen exposures during this vulnerable period remains important given the high risk of serious adverse health effects. These results highlight the lack of access to safe water, sanitation, and hygiene and reinforce the potential importance of anthelmintics as part of CMAM