Susceptibility of spiny rats (Proechimys semispinosus) to Leishmania (Viannia) panamensis and Leishmania (Leishmania) chagasi

The role of Proechimys semispinosus as reservoir of Leishmania (Viannia) panamensis on the Colombian Pacific coast was experimentally evaluated. The susceptibility to L. chagasi also was assessed to determine the utility of this rodent as a model for studying reservoir characteristics in the laboratory. Wild-caught animals were screened for natural trypanosomatid infections, and negative individuals were inoculated intradermally (ID) in the snout or feet with 10(7) promastigotes of L. panamensis. L. chagasi was inoculated intracardially (10(7) promastigotes) or ID in the ear (10(8) promastigotes). PCR-hybridization showed that 15% of 33 spiny rats were naturally infected with L. Viannia sp. Animals experimentally infected with L. panamensis developed non-ulcerated lesions that disappeared by the 7th week post-infection (p.i.) and became more resistant upon reinfection. Infectivity to sand flies was low (1/20-1/48 infected/fed flies) and transient, and both culture and PCR-hybridization showed that L. panamensis was cleared by the 13th week p.i. Animals inoculated with L. chagasi became subclinically infected and were non-infective to sand flies. Transient infectivity to vectors of spiny rats infected with L. panamensis, combined with population characteristics, e.g., abundance, exploitation of degraded habitats and high reproductive rates, could make them epidemiologically suitable reservoirs.

Susceptibility to diazinon in populations of the horn fly, Haematobia irritans (Diptera: Muscidae), in Central Brazil

From October 2000 to April 2001, insecticide bioassays were conducted in 18 ranches from 10 counties in the states of Mato Grosso and Mato Grosso do Sul, in Central Brazil. Horn flies from wild populations were exposed to diazinon-impregnated filter papers immediately after collection on cattle, and mortality was recorded after 2 h. A high susceptibility to diazinon was observed in all tested populations. The LC50s ranged from 0.15 to 0.64 µg/cm², and resistance ratios were always lower than one (ranging 0.1-0.6). Pyrethroid products, most applied by backpack sprayers, have been used since the horn fly entered the region, about 10 years ago. The high susceptibility observed to diazinon indicates that this insecticide (as probably other organophosphate insecticides) represents an useful tool for horn fly control and resistance management, particularly in pyrethroid-resistant populations.

Quantifying the potential pathogens transmission of the blowflies (Diptera: Calliphoridae)

To quantify the potential capability of transporting and passing infective pathogens of some blowflies (Diptera: Calliphoridae), Mihályi's danger-index was calculated for seven species. The original equation was modified to include synanthropic information to discriminate between asynanthropic, hemisynanthropic, and eusynanthropic status. Three groups were recognized, of which Phaenicia cluvia and Musca domestica proved the flies with lowest index value (D = 2.93 and 3.00 respectively); Cochliomyia macellaria, Chrysomya albiceps and Sarconesia chlorogaster presented a significantly higher index value (p < 0.10; D = 4.28, 4.44 and 5.66 respectively) and C. megacephala, C. vicina and P. sericata appear to represent the heaviest potential sanitary risk with the highest index value (p < 0.10; D = 15.54, 16.88 and 12.49 respectively).

Detection of amastigote-like forms in the valve of Phlebotomus papatasi infected with Leishmania major

A massive and homogeneous amount of amastigote-like forms was detected in the stomodeal valve (SV) and the thoracic mid-gut (TMG) of Leishmania major-infected Phlebotomus papatasi, which received a second blood meal 13 to 21 days post-infection on healthy anaesthetized hamsters. After re-feeding, the infected sand flies were dissected out to examine the morphology of the parasite in SV, TMG and the abdominal mid-gut (AMG). Different promastigote forms were seen in the infected flies. Among these included typical promastigotes (nectomonads and haptomonads), paramastigotes, metacyclic promastigotes and, in some samples, the here-reported amastigote-like forms. The Leishmania amastigote-like forms were detected in the SV of sand flies with 14, 18 and 21 days of infection as well as in the TMG at 13 and 18 days post-infection. However, the amastigote-like forms were not detected in the AMG. Factors such as the acidic pH predominating the TMG and the SV, as well as the temperature of the ingested blood, among others, are suggested as contributing to the transformation of the typical promastigotes into the amastigote-like forms. The significance of this finding is discussed and the possible biological advantage for transmission of Leishmania is considered.

Recent observations on the sand fly (Diptera: Psychodidae) fauna of the State of Rondônia, Western Amazônia, Brazil: the importance of Psychdopygus davisi as a vector of zoonotic cutaneous leishmaniasis

Sand flies were collected in the central region of the state of Rondônia (W 64º30' to 63º00' and S 10º00'to 11º00') using Shannon and CDC light traps from October 1997 to August 2000. A total of 85,850 specimens representing 78 named species were captured. Of these 14 were new records for Rondônia. The proportion of males/females was 1/1.131. Trypanosomatids, that are presently being identified, were detected in 11 species. Leishmania (Viannia) naiffi was recorded from Psychodopygus davisi and P. hirsutus. In the present study the dominant species was P. davisi (39.6%) followed by Lutzomyia whitmani (13.1%), P. carrerai (11.6%), and P. hirsutus (10.2%). The importance of P. davisi as a vector of zoonotic cutaneous leishmaniasis is discussed.

Host characteristics do not affect community structure of ectoparasites on the fishing bat Noctilio leporinus (L., 1758) (Mammalia: Chiroptera)

Patterns of parasite abundance and prevalence are thought to be influenced by several host characteristics such as size, sex, developmental stage, and seasonality. We examined two obligatory ectoparasites of the bat Noctilio leporinus (L.) (Chiroptera, Noctilionidae) to test whether prevalence and abundance of Noctiliostrebla aitkeni Wenzel and Paradyschiria fusca Speiser (Diptera, Streblidae) are influenced by the host characteristics. During this survey, 2110 flies were collected. The total abundance was 1150 N. aitkeni and 950 P. fusca. The prevalence of both species was shown to be superior to 75% and neither host size, sex, reproductive stage nor season influenced significantly the variation of the observed values. N. aitkeni were more abundant than P. fusca in all seasons except winter. Both flies showed a significant seasonal variation in terms of abundance but host biological characteristics (host size, sex, and reproductive stage) did not play a significant role as structuring factors of the batflies component community.

Seasonal transmission of Leishmania (Leishmania) mexicana in the state of Campeche, Yucatan Peninsula, Mexico

In the Yucatan Peninsula, Mexico, localized cutaneous leishmaniasis (LCL) caused by Leishmania (Leishmania) mexicana is a typical wild zoonosis restricted to the forest, and humans are only accidentally involved. The transmission of L. (L.) mexicana has been related to the patient's occupation: "chicleros"(gum collectors) and agricultural workers. The objective of this study was to document L. (L.) mexicana seasonally of transmission in endemic areas of LCL in the state of Campeche, Yucatan Peninsula, Mexico. The timing of incidence of LCL in humans during 1993-1994, as well as the rate and time of infection in rodents and sand flies between February 1993 and March 1995 were analyzed. Rodents and sand flies were found infected between November and March, when men carried out their field activities and are exposed. Based on results analyzed, it is concluded that L. (L.) mexicana in the endemic area of LCL in the state of Campeche, Yucatan Peninsula, Mexico, presents a seasonal transmission restricted to the months of November to March. The knowledge of the timing of the transmission cycle in an endemic area of leishmaniasis is very important because intervention measures on the high-risk focus and population might be restricted.

Redescription of Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) (Diptera: Psychodidae)

The phlebotomine sand flies Nyssomyia intermedia and Nyssomyia neivai are the probable vectors of American tegumentary leishmaniasis in the Southern and Southeastern regions of Brazil. These species form a complex, being difficult to separate between either females or males of the two members based on recognized morphological characteristics. Both N. intermedia and N. neivai are redescribed here in the search for characters that facilitate their correct identification. It was possible to differentiate females by means of spermathecal characteristics. Males could be separated with confidence by the tips of the genital filaments, which have the form of a deep spoon, the angle of the concavity being well accentuated in N. intermedia and much shallower in N. neivai.

Biology of the first generation of a laboratory colony of Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) (Diptera: Psychodidae)

The phlebotomine sand flies Nyssomyia intermedia (Lutz & Neiva, 1912) and Nyssomyia neivai (Pinto, 1926) are very close and may be involved in the transmission of Leishmania spp. Ross, 1903 in Brazil. The biology of the first laboratory-reared generations of these species, descended from insects captured in Além Paraíba (N. intermedia) and Corinto (N. neivai) in the Brazilian state of Minas Gerais, is described here. The captured females were fed on hamsters and maintained individually in rearing pots. Laboratory temperature and relative humidity were maintained at 25-26ºC and 80% respectively. The productivity of the first generation of N. intermedia was greater than that of N. neivai, and its development time clearly shorter, particularly for the second and third larval instars.

Study on phlebotomine sand fly (Diptera: Psychodidae) fauna in Belo Horizonte, state of Minas Gerais, Brazil

A study on the phlebotomine sand fly fauna in Belo Horizonte city, state of Minas Gerais, Brazil, was carried out. From April 2001 to March 2003, monthly systematic collections were performed in three houses from each of the nine regions of the city, using CDC light traps for four consecutive days. The traps were set into the houses and in peridomestic areas totaling 54 traps. A number of 3871 sand fly specimens of the genera Lutzomyia and Brumptomyia were collected. Sixty eight percent of the specimens were L. longipalpis and 16% L. whitmani, insect vectors of visceral and American cutaneous leishmaniasis, respectively. Environmental factors such as temperature, humidity, and frequency of precipitation suggest that the number of insects increases after rainy periods. During the same period mentioned above, seasonal captures were carried out in parks and green areas of Belo Horizonte, using Shannon trap. A total of 579 phlebotomine sand flies were collected from which 398 (68.7%) were females with the predominance of L. whitmani and L. monticola. Those specimens were used for natural infection examination, by polymerase chain reaction. No Leishmania DNA was present in any of the specimens tested.

Moonlight and blood-feeding behaviour of Lutzomyia intermedia and Lutzomyia whitmani (Diptera:Psychodidae:Phlebotominae), vectors of American cutaneous leishmaniasis in Brazil

Lutzomyia intermedia (Lutz & Neiva, 1912) and L. whitmani (Antunes & Coutinho, 1939) (Diptera: Psychodidae: Phlebotominae), two important vectors of American cutaneous leishmaniasis in Brazil, occur in sympatry in the locality of Posse county, Petrópolis municipality, state of Rio de Janeiro, Brazil. We investigated the influence of the lunar cycle on the frequency of specimens of the two species caught while attempting to bite the collectors and in CDC light traps. Analysis of the numbers of sand flies captured in different lunar phases for two consecutive years in the peridomestic site and forest shows that there is a significant positive correlation between moonlight intensity and the numbers of L. intermedia and L. whitmani females collected while blood-feeding, whereas the opposite was observed for the CDC traps.

Multiplex-PCR for detection of natural Leishmania infection in Lutzomyia spp. captured in an endemic region for cutaneous leishmaniasis in state of Sucre, Venezuela

We studied the natural infection of Lutzomyia (Lutzomyia) sp. with Leishmania in endemic foci of cutaneous leishmaniasis in the Paria peninsula, state of Sucre, Venezuela. Sand flies were collected between March 2001 and June 2003, using Shannon light-traps and human bait. Of the 1291 insects captured, only two species of phlebotomines were identified: L. ovallesi (82.75%) and L. gomezi (17.42%). A sample of the collected sand flies (51 pools of 2-12 individuals) were analyzed by using a multiplex-PCR assay for simultaneous detection of New Word Leishmaniaand Viannia subgenera. The results showed a total of 8 pools (15.68%) infected; of these, 7 were L. ovallesi naturally infected with L. braziliensis (2 pools) and L. mexicana (5 pools) and 1 pool of L. gomezi infected by L. braziliensis.

Lutzomyia longipalpis in Clorinda, Formosa province, an area of potential visceral leishmaniasis transmission in Argentina

Phlebotomine captures were performed during 2004 in Clorinda, Argentina. Clorinda is located across the branches of the Paraguay river in front of Asunción city, Paraguay. Reports of canine and human visceral leishmaniasis in Asunción have been increasing since 1997, however neither leishmaniasis cases nor sand flies were ever recorded from Clorinda. Light traps were located in migration paths (bridges, port), and peridomestic environments of Clorinda and surrounding localities. Lutzomyia longipalpis was found in Clorinda and Puerto Pilcomayo, first report in a potential visceral leishmaniasis transmission area for Argentina. Active surveillance is required immediately in the localities involved and the surrounding area.

Dispersal pattern of the sand fly Lutzomyia neivai (Diptera: Psychodidae) in a cutaneous leishmaniasis endemic rural area in Southeastern Brazil

The dispersal pattern of the sand fly Lutzomyia neivai was studied through mark-release-recapture experiments in an American cutaneous leishmaniasis endemic rural area in Southeastern Brazil. Over 6500 specimens were marked with fluorescent powder and released in forest edge and peridomicile habitats from August to November 1999, February and April 2000. Recapture attempts were made using Shannon and CDC traps up to eight successive nights after releases. A total of 493 (7.58%) specimens were recaptured. The number of recaptured males and females of L. neivai in CDC traps was not affected by the distance between the trap and the release points. Approximately 90% of males and females recaptured in CDC traps were caught up to 70 m from the release points. The maximum female flight range recorded was 128 m. The average flight range per day was less than 60 m for males and females. Of the flies released in forest edge, approximately 16% of the recaptured females were caught in Shannon traps in the peridomicile habitat. The results indicate that the movements of L. neivai are spatially focal and the possibility of dispersion from forest to peridomicile habitat may be an important way of contracting leishmaniasis in dwellings.

Lutzomyia longipalpis and the eco-epidemiology of American visceral leishmaniasis, with particular reference to Brazil: a review

An historical review is given of American visceral leishmaniasis (AVL), with particular reference to the eco-epidemiology of the disease in Brazil. Following the first records of AVL in this country, in 1934, the sandfly Lutzomyia longipalpis (Lutz and Neiva, 1912) was incriminated as the principal vector. It is now generally accepted, however, that there exist a number of cryptic species under the name of Lu. longipalpis s.l. and that variations in the quantity of the vasodilatory peptide maxadilan in the saliva of flies from different populations of Lu. longipalpis s.l., may account for the variable clinical manifestations of AVL seen in different geographic regions. Distribution of AVL has been shown to extend throughout most of South and Central America, with the domestic dog serving as the principal reservoir of infection for man. However, while one hypothesis suggests that the causative parasite is Leishmania infantum, imported from Europe with the Portuguese and Spanish colonists, the demonstration of a high rate of benign, inapparent infection in foxes in Amazonian Brazil raised an opposing suggestion that the parasite is indigenous to the Americas. Recent reports of similar infections in native marsupials, and possibly rodents, tend to support this view, particularly as Lu. longipalpis is primordially a silvatic sandfly. Although effective control measures in foci of the disease will diminish the number of canine and human infections, the presence of such an enzootic in a variety of native animals will render the total eradication of AVL unlikely.