Samuel T Darling – Pioneer and Malariologist

Samuel T Darling – Pioneer and Malariologist

Sam Darling, founder of NO MO Foundation and inventor of NO MO repellent is the grandson of Dr. Samuel Taylor Darling (1872 -1925). Sam grew up with a deep awareness of his grandfather’s legacy. During the early twentieth century, Dr. Darling was one of the world’s leading experts in tropical diseases.

He investigated malaria and other mosquito-borne diseases in Panama, the Far East, South Africa, Brazil and the southern United States. As a pathologist, he performed more than 4,000 autopsies on employees of the Panama Canal company who died between 1905 and 1914. This experience gave him a singular perspective on the anatomical pathology of tropical diseases. The results of his innovative work helped him to develop new concepts about diagnosis and treatment of malaria. In memory of his contribution to an understanding of malaria, the mosquito responsible for most malaria in Latin America (Anopheles darlingi) was named for him. Indeed, the efforts of the NO MO Foundation to reduce mosquito-borne disease in Africa are inspired by Dr. Darling’s own work on behalf of those who suffer most from mosquito borne disease: the poor.

Enrique Chaves-Carballo found Dr. Darling’s life so interesting, he wrote a book called The Tropical World of Samuel Taylor Darling ~ Parasites, Pathology and Philanthropy. Dr. Chaves-Caballo’s primary research was conducted at the Rockefeller Archives, National Archives, the US Library of Congress, and libraries in the former Canal Zone of Panama. His book is essential reading for medical historians and those interested in the history of sanitation, public health, malaria, and yellow fever. It provides a good understanding of the early twentieth century Panama Canal experience, and the Rockefeller philanthropy in tropical medicine and hygiene.

In response to Chaves-Carballo’s book, Dr. Gerald L. Baum, M.D. Professor of Medicine at Sackler School of Medicine, Tel Aviv University, states “This biography emphasizes not only the remarkable person that was Samuel Taylor Darling, but also redirects our attention to the terrible world of parasite infestation of humans. The shock comes from realizing that what Dr. Darling had to deal with almost one hundred years ago is still a major problem in a great part of the world today.”

In reflecting upon vector borne diseases, Dr. Baum makes an important link to poverty “The failure to achieve better control of these problems is closely related not only to personal poverty, but poverty of governments that cannot afford to establish effective public health systems. In addition the lack of means in a large part of the world results in the crowding and poor hygiene that fosters the spread of these diseases.” 

In his most recent endorsement of the NO MO Foundation Dr. Chaves-Carbello states that “many approaches have been directed to reduce the number of cases and deaths from malaria. Each of these has advantages and disadvantages. For example, insecticide-treated bed nets are often provided free, but many recipients do not use them, or they use them inappropriately. Additionally, a malaria vaccine initiative has not produced good results, as protection has been insufficient. Finally, insect repellents containing DEET have shown limited efficacy against important disease vectors and they’re too costly for poor populations. However, the product developed by Samuel Darling and the NO MO initiative has provided 100% protection for 10 hours in EPA-required field trials. In addition, the product is distributed below cost, thanks to contributions from concerned individuals. I urge everyone to contribute to this lofty endeavour by the NO MO Foundation to protect the lives of African children.”

EPA-Required Field Efficacy Test in Two Environments

EPA-Required Field Efficacy Test in Two Environments

The objective of the test was to determine the Complete Protection Time of NO MAS repellent (NO MO), when applied at a typical consumer dose, again wild populations of mosquitos including but not limited to species of the genera Culex, Anopheles, and Aedes, to provide data under the Data-Call-In requirements (EPA Reg. No. 3126-LRN0) of United States Environmental Protection Agency Guideline OPPTS 810.3700.

This mosquito repellent study was sponsored by Mr. Sam Darling of the Del Cielo foundation (Salt Spring Island, British Columbia, Canada), to provide efficacy data in support of a pesticide registration application to the United States Environmental Protection Agency. The test material, based on the active ingredients p-menthane-3,8-diol (PMD) and lemongrass oil (citral), is No Mas, a topical lotion repellent.

The study Protocol was reviewed and approved by Independent Investigational Review Board, Inc., and reviewed favorably by the US Environmental Protection Agency and its Human Studies Review Board, and by the California Environmental Protection Agency.

We conducted a dosimetry study in advance of efficacy testing in order to estimate typical consumer dosing behavior. The resulting average dosing rates, of 1.20 μl/cm2 on arms and 1.04 μl/cm2 on legs, were then employed as the rates for the subjects in the field efficacy study. These results were also used to estimate the Margin of Exposure (MOE) relative to acute dermal toxicity limit dose in No Mas (>5000 mg/kg, see toxicity test reports), resulting in Margin of Exposure (MOE) values of >583 (arms) and >287 (legs) for the repellent. We judged these margins to be sufficiently great to justify dermal exposure of the subjects to the test materials during efficacy testing.

Efficacy was tested in two different habitats under expected environmental conditions for consumers using the product. In each habitat, ten human subjects (five female, five male) each exposed a No Mas repellent-treated limb to mosquitoes for one minute every 15 minutes, until product failure or cessation of the test. Simultaneously, one male and one female untreated control subject exposed arms or legs in the same manner, in order to assess mosquito biting pressure. Both controls experienced landings within one minute of exposure throughout each test day, indicating that mosquitoes were suitably active for the efficacy study.

Under field conditions, the repellent provided substantial and prolonged protection against the mosquito species (Aedes melanimon, Ae. vexans, Ae.nigromaculis, Culex tarsalis, and Anopheles freeborni). Mean Complete Protection Time (CPT) for No Mas was 9.8 hours at Site 1 and 10.1 hours at Site 2.

In summary, No Mas repellent at 16% PMD and 2% lemongrass oil concentrations provided prolonged periods of Complete Protection against several species of mosquitoes, including species significant to public health.

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A Community-Wide Study of Malaria Reduction in Ghana 

A Community-Wide Study of Malaria Reduction in Ghana 

NO MAS (NO MO) mosquito repellent was evaluated in two farming villages (4 km apart) in the Kassena Nankana district of northern Ghana. We determined its efficacy against local malaria vectors, degree of user acceptance, and its effect on malaria prevalence in households using insecticide-treated bed nets.

The average protective efficacy of NM against Anopheles mosquitoes over 9 hours was 89.6%. Controls averaged 86 bites/person/night versus 9 bites/ person/night with the use of NM. Use of repellent was associated with a decrease of absolute malaria prevalence by 19.2% in the repellent village and by 6.5% in the control village (45.5 to 26.3, and 29.5 to 23.0, respectively). The user acceptance rate of NM repellent was 96.1%. Ten percent (10%) of repellent users reported irritation as the main adverse effect during the period. Eighty-five percent (85%) of the users found the odor of NM appealing and 87% reported no inconvenience in applying the repellent daily.

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Estimating a Repellent’s Potential to Reduce Malaria in Communities

Estimating a Repellent’s Potential to Reduce Malaria in Communities

A static probability model is presented to simulate malaria infection in a community during a single transmission season. The model includes five parameters—sporozoite rate, human infection rate, biting pressure, repellent efficacy, and product-acceptance rate.

Background & objective: Probability models for assessing a mosquito repellent’s potential to reduce malaria transmission are not readily available to public health researchers. To provide a simple means for estimating the epidemiological efficacy of mosquito repellents in communities, we develop a simple mathematical model.

Study design: A static probability model is presented to simulate malaria infection in a community during a single transmission season. The model includes five parameters—sporozoite rate, human infection rate, biting pressure, repellent efficacy, and product-acceptance rate.

Interventions: The model assumes that a certain percentage of the population uses personal mosquito repellents over the course of a seven-month transmission season and that this repellent maintains a constant rate of protective efficacy against the bites of malaria vectors.

Main outcome measures: This model measures the probability of completely evading infection over a seven-month period at diverse rates of vector biting pressure, repellent efficacy, and product acceptance.

Results & conclusion: Absolute protection using mosquito repellents alone requires high rates of repellent efficacy and product acceptance. Using performance data from a highly effective repellent, the model estimates an 88.9% reduction of infections over a seven-month transmission season. A corresponding and proportional reduction in the incidence of super-infection in community members not completely evading infection can also be presumed. Thus, the model shows that mass distribution of a repellent with >98% efficacy and >98% product acceptance would suppress new malaria infections to levels lower than those achieved with insecticide treated nets (ITNs). A combination of both interventions could create synergies that result in reductions of disease burden significantly greater than with the use of ITNs alone.

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Repellent Test: Aedes aegypti, a vector for dengue, yellow fever and Zika

Repellent Test: Aedes aegypti, a vector for dengue, yellow fever and Zika

Procedure: The 018-A formulation of NO MAS was evaluated on skin for repellency to female Aedes aegypti mosquitoes. In a single repellent duration test, a 1 milliliter dose of the formulation was applied to the left forearm of the test volunteer. The formulation was spread evenly from wrist to elbow (on approximately 650 cm2 of skin surface area) and evaluated for repellency to caged female mosquitoes. One hour after the application of the formulation, the treated arm was exposed for 3 min to mosquitoes and then re-exposed in the same manner at hourly intervals thereafter until repellent failure. The test was conducted in a 40 cm3 cage containing 200 (6-9 day-old) female Aedes aegypti mosquitoes preselected for testing on the basis of demonstrated human host avidity. Repellency was calculated as Complete Protection Time (CPT), i.e., the time between repellent application and 2 or more probings of the skin on the treated arm, or the first probing followed by another probing within 30 min. A glove was worn to protect the untreated hand from mosquito bites during testing. Two negative controls were used in each test (observed once per hour until repellent failure) and comprised the number of female mosquitoes in the test cage and in a (separate) control cage that landed and remained on the untreated skin of the right forearm of the test volunteer for > 5 sec during a 10 second exposure period.

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Ghana: Test of NO MAS (NO MO) against simulium damnosum

Ghana: Test of NO MAS (NO MO) against simulium damnosum

Full Title: Efficacy of DEET-Based Repellents and NO MAS (NO MO) against Bites of Blackflies (Simulium damnosum), a Vector for Onchocerciasis

Coping strategies including smoke screens are used against nuisance bites of Simulium damnosum  Theobald (Diptera:Simuliidae) in onchocerciasis endemic communities. To find more effective alternatives, the efficacy of commercially available N ,N -diethyl-3-methylbenzamide (DEET) products with active concentrations of 9.5, 13, 25, 50 and 98.1–100% and ‘NO MAS,’ (active component: para-menthane-3,8-diol and lemon grass oil) were tested at Bui-Agblekame, Ghana. A Latin square study design was implemented using eight groups of two vector collectors each, who used repellents (treatment), mineral oil or nothing each day until the end of the study. Flies were caught and their numbers each hour recorded using the standard methods for onchocerciasis transmission studies. T -tests were used to compare the mean duration of protection and a one-way analysis of variance controlling for catchers and repellents was performed. Tukey’s test was used to compare protection by repellents and mineral oil. The highest percentage protection was 80.8% by NO MAS and the least 42.5% by the 13% DEET product. The period of absolute protection was 5 h by NO MAS and 1 h by 50% DEET product. No significant increase in protection was offered beyond 25% active DEET products and no significance was observed in terms of catcher Å~  repellent effect (F =  1. 731, d.f. =  48, P =  0. 209).

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