Didilia sp. Infecting Phlebotomus stantoni in Thailand

Nematode infection in wild caught Phlebotomine sand flies was investigated in Thailand. Light microscopy (LM) and scanning electron microscopy (SEM) were used to detect and morphologically characterize entomopathogenic nematodes that presented in the sand flies. Didilia sp. nematodes were found for the first time in the body cavity of wild caught male Phlebotomus stantoni sand flies. The Didilia sp. was identified based on the morphology of the adult nematodes, from their stylet and teeth at the anterior tip, body length, and egg shell sculpture. It was noted that every infected male sand fly had unrotated genitalia, which would not allow them to mate, thus leading to the loss of their offspring. This finding provided information that might lead to study on whether or not the Didilia sp. has the potential to control sand fly population

Species composition and population dynamics of phlebotomine sand flies in a Leishmania infected area of Chiang Mai, Thailand

Phlebotomine sand flies are established vectors of leishmaniasis in humans. In Thailand, Leishmania martiniquensis and “Leishmania siamensis” have been described as causative agents of leishmaniasis. In this study, a survey of sand flies in the Leishmania infected area of Hang Dong district, Chiang Mai, Thailand was performed using CDC light traps for eight consecutive months, from January to August 2016. A total of 661 sand flies were collected, and of 280 female sand flies, four species of the genus Sergentomyia including Sergentomyia gemmea, S. barraudi, S. indica, and S. hivernus and one species of the genus Phlebotomus, Phlebotomus stantoni, were identified. S. gemmea and S. hivernus were found in Chiang Mai for the first time. The density of captured female sand flies was high in warm and humid periods from June to August, with temperatures of around 26°C and relative humidity about 74%. In addition, S. gemmea was the most predominant species in the area. Further studies as to whether or not these sand fly species could be a vector of Leishmaniasis in Thailand are required

Artesunate dose escalation for the treatment of uncomplicated malaria in a region of reported artemisinin resistance: A randomized clinical trial

Background: The emergence of artemisinin resistance has raised concerns that the most potent antimalarial drug may be under threat. The currently recommended daily dose of artesunate (AS) is 4 mg/kg, and is administered for 3 days together with a partner antimalarial drug. This study investigated the impact of different AS doses on clinical and parasitological responses in malaria patients from an area of known artemisinin resistance in western Cambodia. Methods: Adult patients with uncomplicated P. falciparum malaria were randomized into one of three 7-day AS monotherapy regimens: 2, 4 or 6 mg/kg/day (total dose 14, 28 and 42 mg/kg). Clinical, parasitological, pharmacokinetic and in vitro drug sensitivity data was collected over a 7-day inpatient period and during weekly follow-up to 42 days. Results: 143 patients were enrolled (n = 75, 40 and 28 to receive AS 2, 4 and 6 mg/kg/day respectively). Cure rates were high in all treatment groups at 42 days despite almost half the patients remaining parasitemic on Day 3. There was no impact of increasing AS dose on median parasite clearance times, median parasite clearance rates or on the proportion of patients remaining parasitemic on Day 3. However at the lowest dose used (2 mg/kg/d) patients with parasitemia >10,000/μL had longer median (IQR) parasite clearance times than those with parasitemia <10,000/μL (63 (48-75) vs. 84 (66-96) hours, p<0.0001). 19% of patients in the high-dose arm developed neutropenia (absolute neutrophil count <1.0×109/L) by Day 14 and resulted in the arm being halted early. Conclusion: There is no pharmacodynamic benefit of increasing the daily dose of AS (4mg/kg) currently recommended for short-course combination treatment of uncomplicated malaria, even in regions with emerging artemisinin resistance, as long as the partner drug retains high efficacy

Proteases of haematophagous arthropod vectors are involved in blood-feeding, yolk formation and immunity : a review

Ticks, triatomines, mosquitoes and sand flies comprise a large number of haematophagous arthropods considered vectors of human infectious diseases. While consuming blood to obtain the nutrients necessary to carry on life functions, these insects can transmit pathogenic microorganisms to the vertebrate host. Among the molecules related to the blood-feeding habit, proteases play an essential role. In this review, we provide a panorama of proteases from arthropod vectors involved in haematophagy, in digestion, in egg development and in immunity. As these molecules act in central biological processes, proteases from haematophagous vectors of infectious diseases may influence vector competence to transmit pathogens to their prey, and thus could be valuable targets for vectorial control

Human population movement and behavioural patterns in malaria hotspots on the Thai–Myanmar border: implications for malaria elimination

Background Malaria is heterogeneously distributed across landscapes. Human population movement (HPM) could link sub-regions with varying levels of transmission, leading to the persistence of disease even in very low transmission settings. Malaria along the Thai–Myanmar border has been decreasing, but remains heterogeneous. This study aimed to measure HPM, associated predictors of travel, and HPM correlates of self-reported malaria among people living within malaria hotspots. Methods 526 individuals from 279 households in two malaria hotspot areas were included in a prospective observational study. A baseline cross-sectional study was conducted at the beginning, recording both individual- and household-level characteristics. Individual movement and travel patterns were repeatedly observed over one dry season month (March) and one wet season month (May). Descriptive statistics, random effects logistic regressions, and logistic regressions were used to describe and determine associations between HPM patterns, individual-, household-factors, and self-reported malaria. Results Trips were more common in the dry season. Malaria risk was related to the number of days doing outdoor activities in the dry season, especially trips to Myanmar, to forest areas, and overnight trips. Trips to visit forest areas were more common among participants aged 20–39, males, individuals with low income, low education, and especially among individuals with forest-related occupations. Overnight trips were more common among males, and individual with forest-related occupations. Forty-five participants reported having confirmed malaria infection within the last year. The main place of malaria blood examination and treatment was malaria post and malaria clinic, with participants usually waiting for 2–3 days from onset fever to seeking diagnosis. Individuals using bed nets, living in houses with elevated floors, and houses that received indoor residual spraying in the last year were less likely to report malaria infection. Conclusion An understanding of HPM and concurrent malaria dynamics is important for consideration of targeted public health interventions. Furthermore, diagnosis and treatment centres must be capable of quickly diagnosing and treating infections regardless of HPM. Coverage of diagnosis and treatment centres should be broad, maintained in areas bordering malaria hotspots, and available to all febrile individuals.</p

Spatial heterogeneity and temporal trends in Malaria on the Thai–Myanmar Border (2012–2017): a retrospective observational study

Malaria infections remain an important public health problem for the Thai-Myanmar border population, despite a plan for the elimination by the end of 2026 (Thailand) and 2030 (Myanmar). This study aimed to explore spatiotemporal patterns in Plasmodium falciparum and Plasmodium vivax incidence along the Thai-Myanmar border. Malaria cases among Thai citizens in 161 sub-districts in Thailand's Kanchanaburi and Tak Provinces (2012-2017) were analyzed to assess the cluster areas and temporal trends. Based on reported incidence, 65.22% and 40.99% of the areas studied were seen to be at elimination levels for P. falciparum and P. vivax already, respectively. There were two clear clusters of malaria in the region: One in the northern part (Cluster I), and the other in the central part (Cluster II). In Cluster I, the malaria season exhibited two peaks, while there was only one peak seen for Cluster II. Malaria incidence decreased at a faster rate in Cluster I, with 5% and 4% reductions compared with 4% and 3% reductions in P. falciparum and P. vivax incidence per month, respectively, in Cluster II. The decreasing trends reflect the achievements of malaria control efforts on both sides of the Thai-Myanmar border. However, these clusters could act as reservoirs. Perhaps one of the main challenges facing elimination programs in this low transmission setting is maintaining a strong system for early diagnosis and treatment, even when malaria cases are very close to zero, whilst preventing re-importation of cases

Geometric morphometrics approach towards discrimination of three member species of Maculatus group in Thailand

Members of the Maculatus group are important malaria vectors in the border regions of Thailand. However, the role of each species in malaria transmission remains unclear because of their highly similar morphologies, making them difficult to be differentiated. Whereas An. pseudowillmori may be identified by the color pattern of some scales on abdomen and wings, the distinction between An. maculatus and An. sawadwongporni relies on the wings only. Scales are labile structures, as they may be accidentally removed during capture and transportation to the laboratory. To discriminate among the species of this group, we tested the suitability of geometric techniques. Shape variables were used as input for discriminant analyses and validated reclassification. Both landmark- and outline-based geometric techniques disclosed significant differences between the three species. For the delicate An. maculatus - An. sawadwongporni distinction, the outline-based approach appeared as the most promising, with validated reclassification scores reaching 93%, as compared to 77% obtained by landmark data. For An. pseudowillmori, reclassification scores were 100% and 94%, respectively. Geometric morphometrics may provide an alternative and useful complement for discriminating members of the Maculatus group