Bionomics of malaria vectors in Lao PDR, 2018-2020: entomological surveillance as a key tool for malaria elimination.

BACKGROUND: The Lao PDR National Strategic Plan for malaria control and elimination for year 2021-2025 emphasizes the importance of routine entomological surveillance being conducted in areas with high transmission and in active malaria foci in elimination targeted areas. The collection of entomological surveillance data that is closely linked to recent epidemiological data is crucial for improving impact, as it contributes to the evidence package that supports operational and strategic decision-making of national malaria programmes, as they accelerate their last mile of elimination. METHODS: The Center for Malariology Parasitology and Epidemiology (CMPE) entomology team conducted entomological surveillance activities at 13 sentinel sites in 8 provinces and at active transmission foci sites from 2018 to 2020. The techniques used for the mosquito collection were indoor and outdoor human landing collections (from houses and from cultivation areas) and cattle baited net trap collections. RESULTS: There were 5601 Anopheles mosquito females captured and identified throughout the study, on both human and cow bait. They represented 15 different species or species complexes. The primary malaria vectors as well as the secondary vectors were present in all collection sites in the south, indicating that people living in these rural areas with high malaria incidence are exposed to the vectors. The vectors were highly zoophilic, but they still bite humans throughout the night with a high peak of activity before midnight, both indoors and outdoors. Overall, 17% of the malaria vectors were collected indoors when the people are sleeping. This confirms the importance of bed net use during the night. Thirty-two percent of primary and secondary vectors were collected outdoors at times when people are usually awake and outdoors, which shows that people are exposed to potentially infectious mosquitoes and the importance of personal protection at these times. The findings showed that residual transmission may occur outdoors in the villages, and outside the villages in cultivation fields and forested areas. Epidemiological data showed that transmission was higher in surveillance sites which were targeted as part of a malaria response rather than sentinel sites. CONCLUSIONS: Understanding where and how transmission is persisting, monitoring and mapping vector species distribution in areas with active transmission, monitoring biting trends, and designing evidence based and effective vector control interventions are critical to accelerating progress toward malaria elimination. In this context, the role of entomological surveillance combined with epidemiological data should be considered as a cornerstone in achieving malaria elimination.

A pilot study to investigate the risk of SARS-CoV-2 household transmission following hospital discharge of confirmed cases in Vientiane Capital, Lao PDR.

Background: Global guidelines from the World Health Organization on discharging patients diagnosed with COVID-19 changed in 2021 to a symptom-based rather than negative PCR-based approach. Studies have shown that shedding of viable virus continues for approximately eight days after symptom onset in most patients. In Vientiane, Laos, until now, patients diagnosed with asymptomatic or mild COVID-19 are hospitalised for 2 weeks and then, if they still test PCR positive for SARS-CoV-2, stay for a further week in a designated quarantine hotel before being discharged home. Objective: The aim of this pilot study was to investigate the risk of transmission of SARS-CoV-2 to household contacts of discharged patients who are still PCR-positive following 2-3 weeks quarantine in Vientiane, Lao PDR. Methods: Adult participants, who were resident in Vientiane Capital and who were about to be discharged from hospital (after 2 weeks hospitalisation), or from a quarantine hotel, following a further one-week quarantine, were screened to assess eligibility for the study. The household of each case was visited a maximum of 48 hours before or up to 24 hours after the participant was discharged and a nasopharyngeal swab was taken from all household members. Repeat nasopharyngeal swabs from cases and contacts were taken on day 7 and day 14 after discharge home of each case. Results: Between 20th May 2021 and 27th August 2021, 55 cases and 84 contacts in 27 households were enrolled in the study. The median [range] age of all 139 included participants was 26.5 years [3 months to 83 years] and 83 (60%) were female. By household, the median [range] number of cases and contacts were 1 [1-6] and 3 [1-13] respectively. At discharge home 32/48 (67%) cases tested positive for SARS-CoV-2. By day 7 11 of 47 cases (23%) still tested positive for SARS-CoV-2 by PCR and by day 14 this number was 2/24 (8%). No contacts tested positive during follow up and the numbers tested at the time of discharge of the case, 7 days later and 2 weeks later were 56, 57 and 37 respectively. Loss to follow up at day 7 and day 14 ranged from 15-50% (participants not at home at the time of visits). Conclusion: In this pilot study we found no evidence of onward transmission of SARS-CoV-2 to contacts of cases discharged home with a positive PCR result. This suggests the current discharge policy for mild to moderate COVID-19 case following 2 weeks in hospital in the Lao PDR is safe.