Browsing by Author "Scott A. Bernhardt"

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Assessing insecticide susceptibility, diagnostic dose and time for the sand fly Phlebotomus argentipes, the vector of visceral leishmaniasis in India, using the CDC bottle bioassay
(Public Library of Science, 2023) Rahul Chaubey; Ashish Shukla; Anurag Kumar Kushwaha; Puja Tiwary; Shakti Kumar Singh; Shawna Hennings; Om Praksh Singh; Phillip Lawyer; Edgar Rowton; Christine A. Petersen; Scott A. Bernhardt; Shyam Sundar
Visceral leishmaniasis (VL) is a vector-borne protozoan disease, which can be fatal if left untreated. Synthetic chemical insecticides are very effective tools for controlling of insect vec-tors, including the sand fly Phlebotomus argentipes, the vector of VL in the Indian subconti-nent. However, repeated use of the same insecticide with increasing doses potentially can create high selection pressure and lead to tolerance and resistance development. The objec-tive of this study was to determine the lethal concentrations and assess levels of susceptibility, diagnostic doses and times to death of laboratory-reared P. argentipes to five insecticides that are used worldwide to control vectors. Using the Center for Disease Control and Prevention (CDC) bottle bioassay, 20–30 sand flies were exposed in insecticide-coated 500-ml glass bot-tles. Flies were then observed for 24 hours and mortality was recorded. Dose-response survival curves were generated for each insecticide using QCal software and lethal concentrations causing 50%, 90% and 95% mortality were determined. A bioassay was also conducted to determine diagnostic doses and diagnostic times by exposing 20–30 flies in each bottle containing set concentrations of insecticide. Mortality was recorded at 10-minute intervals for 120 minutes to generate the survival curve. Phlebotomus argentipes are highly susceptible to alpha-cypermethrin, followed by deltamethrin, malathion, chlorpyrifos, and least susceptible to DDT. Also, the lowest diagnostic doses and diagnostic times were established for alpha-cypermethrin (3μg/ml for 40 minutes) to kill 100% of the flies. The susceptibility data, diagnostic doses and diagnostic times presented here will be useful as baseline reference points for future studies to assess insecticide susceptibility and resistance monitoring of field caught sand flies and to assist in surveillance as VL elimination is achieved in the region. © 2023 Chaubey et al.
Dogs as Reservoirs for Leishmania donovani, Bihar, India, 2018–2022
(Centers for Disease Control and Prevention (CDC), 2024) Anurag Kumar Kushwaha; Ashish Shukla; Breanna M. Scorza; Rahul Chaubey; Dharmendra Kumar Maurya; Tulika Kumari Rai; Shyamali Yaduvanshi; Shweta Srivastava; Gaetano Oliva; Epke A. Le Rutte; Rajiv Kumar; Om Prakash Singh; Puja Tiwary; Shakti Kumar Singh; Scott A. Bernhardt; Phillip Lawyer; Edgar Rowton; Christine A. Petersen; Shyam Sundar
Visceral leishmaniasis derived from Leishmania donovani is transmitted by sand flies (Phlebotomus argentipes) throughout the Indian subcontinent. Although considered anthroponotic, L. donovani infects other mammals susceptible to sand fly bites, including dogs. Aggressive strategies to reduce sand fly populations in India have led to flies seeking nonhuman hosts, so understanding the role of dogs in L. donovani transmission has become critical. Our study investigated L. donovani infection in dogs and the potential for such infections to be transmitted back to sand flies. We performed xenodiagnosis by using P. argentipes on dogs (n = 73) with quantitative PCR–detectible parasitemia in both endemic and outbreak villages. We found that 12% (9/73) of dogs were infectious to sand flies during winter and rainy seasons. Patients with visceral leishmaniasis remain primary sources of L. donovani transmission, but our findings suggest a possible link between canine infection and human exposure. © 2024 Centers for Disease Control and Prevention (CDC). All rights reserved.
Livestock and rodents within an endemic focus of Visceral Leishmaniasis are not reservoir hosts for Leishmania donovani
(Public Library of Science, 2022) Anurag Kumar Kushwaha; Ashish Shukla; Breanna M. Scorza; Tulika Kumari Rai; Rahul Chaubey; Dharmendra Kumar Maurya; Shweta Srivastva; Shreya Upadhyay; Abhishek Kumar Singh; Paritosh Malviya; Om Prakash Singh; Vivek Kumar Scholar; Puja Tiwary; Shakti Kumar Singh; Phillip Lawyer; Edgar Rowton; Scott A. Bernhardt; Christine A. Petersen; Shyam Sundar
Leishmaniasis on the Indian subcontinent is thought to have an anthroponotic transmission cycle. There is no direct evidence that a mammalian host other than humans can be infected with Leishmania donovani and transmit infection to the sand fly vector. The aim of the present study was to evaluate the impact of sand fly feeding on other domestic species and provide clinical evidence regarding possible non-human reservoirs through experimental sand fly feeding on cows, water buffalo goats and rodents. We performed xenodiagnosis using colonized Phlebotomus argentipes sand flies to feed on animals residing in villages with active Leishmania transmission based on current human cases. Xenodiagnoses on mammals within the endemic area were performed and blood-fed flies were analyzed for the presence of Leishmania via qPCR 48hrs after feeding. Blood samples were also collected from these mammals for qPCR and serology. Although we found evidence of Leishmania infection within some domestic mammals, they were not infectious to vector sand flies. Monitoring infection in sand flies and non-human blood meal sources in endemic villages leads to scientific proof of exposure and parasitemia in resident mammals. Lack of infectiousness of these domestic mammals to vector sand flies indicates that they likely play no role, or a very limited role in Leishmania donovani transmission to people in Bihar. Therefore, a surveillance system in the peri-/post-elimination phase of visceral leishmaniasis (VL) must monitor absence of transmission. Continued surveillance of domestic mammals in outbreak villages is necessary to ensure that a non-human reservoir is not established, including domestic mammals not present in this study, specifically dogs. © 2022 Kushwaha et al.
Monitoring alpha-cypermethrin susceptibility of Phlebotomus argentipes, the vector of visceral leishmaniasis in India, using the CDC bottle bioassay
(BioMed Central Ltd, 2024) Rahul Chaubey; Ashish Shukla; Anurag Kumar Kushwaha; Shakti Kumar Singh; Om Prakash Singh; Rajiv Kumar; Phillip Lawyer; Edgar Rowton; Christine A. Petersen; Scott A. Bernhardt; Shyam Sundar
Background: Visceral leishmaniasis (VL), known as Kala-azar on the Indian subcontinent, is a parasitic disease caused by the flagellated protozoa Leishmania donovani and can be fatal if left untreated. The sand fly Phlebotomus argentipes is the only proven vector of VL in the Southeast Asia region, and VL control in this region has relied on the use of synthetic insecticides for indoor residual spraying (IRS). The use of DDT in VL control programmes has led to the development of resistance to this insecticide in sand flies, resulting in DDT being replaced with the insecticide alpha-cypermethrin. However, alpha-cypermethrin has a similar mode of action as DDT and, therefore, the risk of resistance development in sand flies increases under the pressure of regular exposure to this insecticide. In the present study we assessed the susceptibility status of wild-caught sand flies and F1 progeny using the CDC bottle bioassay. Methods: Sand flies were collected from 10 villages in Muzaffarpur District, Bihar, India. Eight of these villages are receiving continuous IRS with alpha-cypermethrin, one village had discontinued IRS with alpha-cypermethrin and one village had never received IRS with alpha-cypermethrin. The collected sand flies were exposed to a pre-determined diagnostic dose for a specific time duration (3 µg/ml for 40 min), and knockdown and mortality at 24 h post-exposure were recorded. Results: Knockdown ranged from 91.19% to 99.47% for wild-caught sand flies and from 91.70% to 98.89% for their F1 progeny. At 24 h post-exposure, mortality ranged from 89.34% to 98.93% for wild-caught sand flies and from 90.16% to 98.33% for F1 progeny. Conclusions: The results of this study showed that P. argentipes is potentially developing resistance, signalling the need for continuous monitoring and vigilance to sustain the validation of elimination once achieved. © The Author(s) 2024.