[Effectiveness of Bacillus sphaericus strain 2362 on larvae of Anopheles nuñeztovari]. / Evaluación de la efectividad de Bacillus sphaericus cepa 2362 sobre larvas de Anopheles nuñeztovari. Mérida, Venezuela.

A study, under laboratory and field conditions, was conducted to evaluate the effectiveness, persistence in the time and some factors that can affect the larvicidal action of the Griselef formulation of the sporogenous bacteria Bacillus sphaericus strain 2362, on the larvae population of the Anopheles nuñeztovari Gabaldón, the main malaria vector in western Venezuela. The degree of susceptibility of this species to the Bacillus sphaericus was determined to be at a LD50 in 0.07 ppm a LD95 in 0.69 ppm. The pH ranges of the water, as tested in the laboratory, showed that values between 7.0 and 9.0 did not affect the action of the larvicide, producing more than 95% of mortality after 72 hours of observation. Under controlled field conditions, the high susceptibility of the An. nuñeztovari larvae to the larvicidal action of the product was demonstrated. With a dose of 5 ml/m2, a 100% mortality was obtained after 72 hours of exposure. In the field, it was determined that after 12 hours, solar radiation decreased the effectiveness of the B. sphaericus in 30% and that the presence of vegetation reduced the biolarvicidal effect between 5 and 12%. Under natural field conditions, it was shown that the larvicide was effective, since a 100% larval mortality was obtained in the two treated breeding places. This effect persisted up to 4 months of observation, with more than 85% of larvae reduction, showing that it is capable or remaining in the natural environment.

Epidemiologic aspects of American visceral leishmaniasis in an endemic focus in Eastern Venezuela.

An endemic focus of American visceral leishmaniasis (AVL) in eastern Venezuela has been evaluated in terms of patients (n = 48), immunologic reactivity to Leishmania in household contacts (n = 187) and neighborhood controls (n = 170), detection of Leishmania (L. donovani complex) in dogs and wild animals by the polymerase chain reaction (PCR) and characteristics of the sandfly population. The male:female ratio of patients was 1.18:1; 89.6% were < or =12 years old. Serologic reactivity was significantly higher in household contacts than in controls (P = 0.0008), as was the size of leishmanin reactions in contacts < or =10 years of age (P = 0.0141). Leishmania donovani complex-specific PCRs were positive in dogs, an opossum (Didelphis marsupialis), and a black rat (Rattus rattus). Lutzomyia longipalpis and Lu. evansi, both implicated in the transmission of AVL, were identified among the 386 sand flies examined. These observations provide the bases for an active control program as well as further studies of reservoirs and vector-host relationships in this area.

Susceptibility of Lutzomyia longipalpis (Diptera: Psychodidae) to selected insecticides in an endemic focus of visceral leishmaniasis in Venezuela.

A field population of Lutzomyia longipalpis from La Rinconada, Lara State, an endemic focus of visceral leishmaniasis in Venezuela, was tested for susceptibility to organochlorine (DDT 2%), carbamate (propoxur 0.01%), organophosphate (malathion 2%, fenitrothion 1%, and pirimiphos methyl 1%), and pyrethroid (deltamethrin 0.06%, lambdacyhalothrin 0.06%, and permethrin 0.2%) insecticides. Susceptibility to the insecticides tested was evaluated in the field population of L. longipalpis and compared with a laboratory reference strain. The (LT95) to propoxur and malathion insecticides for the field population was lower than the LT95 for the laboratory reference strain, demonstrating high susceptibility to these compounds. A low level of resistance at LT50 (< 3-fold) was found for fenitrothion, pirimiphos methyl, and permethrin insecticides, but no resistance was detected at LT95. No significant resistance at the LT50 and LT95 was detected for the pyrethroids deltamethrin and lambdacyhalothrin. The susceptibility levels of L. longipalpis to the insecticides tested are discussed in view of a future control program against endophilic vectors of leishmaniases based on the use of pesticides.

Characterization of resistance to organophosphate, carbamate, and pyrethroid insecticides in field populations of Aedes aegypti from Venezuela.

Resistance to the organophosphates (OP) temephos, malathion, and pirimiphos methyl, and the carbamate propoxur was found to be low (< 5-fold) in 3 Aedes aegypti populations collected from Falcon and Aragua states of Venezuela. Resistance to chlorpyrifos (OP), permethrin, and lambda-cyhalothrin (pyrethroids) was moderate (7-fold) in both populations. Mechanisms of resistance were investigated with the synergists piperonyl butoxide (mixed function oxidase inhibitor) and S, S, S-tributyl phosphorothioate (DEF, an esterase inhibitor). Nonspecific esterase and oxidase enzymes played a significant role in OP and carbamate resistance, respectively. Resistance to pyrethroid insecticides was not affected by DEF or piperonyl butoxide. This suggested the presence of another mechanism such as altered target site sensitivity (kdr). Biochemical tests showed significantly greater amounts of esterase activity in field strains, whereas insensitive acetylcholinesterase was not involved in either OP or carbamate resistance. These results must be considered in future control programs for Ae. aegypti, because OPs and pyrethroids are currently used in vector control in most countries of Central and South America.