Phlebotomine sand flies (Diptera: Psychodidae) transmitting visceral leishmaniasis and their geographical distribution in China: a review.

After the existence of phlebotomine sand flies was first reported in China in 1910, the distribution of different species and their role in the transmission of visceral leishmaniasis (VL) have been extensively studied. Up until 2008, four species have been verified as vectors of VL, namely, Phlebotomus chinensis (Ph. sichuanensis), Ph. longiductus (Ph. chinensis longiductus), Ph. wui (Ph. major wui), and Ph. alexandri. The sand fly species vary greatly depending on the natural environments in the different geographic areas where they are endemic. Ph. chinensis is euryecious and adaptable to different ecologies, and is thus distributed widely in the plain, mountainous, and Loess Plateau regions north of the Yangtze River. Ph. longiductus is mainly distributed in ancient oasis areas south of Mt. Tianshan in the Xinjiang Uygur autonomous region. Ph. wui is the predominant species in deserts with Populus diversifolia and Tamarix vegetation in Xinjiang and the western part of the Inner Mongolia autonomous region. Finally, Ph. alexandri is steroecious and found only in stony desert areas, such as at the foot of the mountains in Xinjiang and the western Hexi Corridor, in Gansu province. This review summarized the relationship between the geographic distribution pattern of the four sand fly species and their geographical landscape in order to foster research on disease distribution and sand fly control planning. Furthermore, some problems that remained to be solved about vectors of VL in China were discussed.

[Identification of three common sandfies in southern Xinjiang with multiplex PCR].

Based on the variable part of mtDNA CO I gene sequence, a multiplex PCR method was developed for the identification of the three common sandflies (Phlebotomus longiductus, Ph. wui, and Ph. alexandri) in southern Xinjiang. The results demonstrated that this multiplex PCR method was reliable, and could be used to identify the three Phlebotomus species. The PCR product of CO I gene from Ph. longiductus, Ph. wui and Ph. alexandri was 248, 632, and 395 bp, respectively.

[Investigation on transmitting vectors of visceral leishmaniasis in Jiashi County, Xinjiang].

OBJECTIVE: To investigate sandfly vectors transmitting visceral leishmaniasis, including species and seasonal distribution in Jiashi county of Xinjiang Uygur Autonomous Region. METHODS: Sandflies were collected in the field, counted and identified. The specimens were dissected to analyze the gonotrophic cycle and to find infection of promastigotes. The resting places were observed by using oil-paper and sandfly-capturing trap. RESULTS: 4540 sandflies were collected with 99.9% of Phlebotomus wui and only 0.1% Sergentomyia minutus sinkiangensis. On the seasonal distribution, the first peak appeared by the end of May and the first ten-day of June, and the second peak was in the middle of August. Observation showed that the activity of sandflies occurred mainly from 22:00 to 4:00, reaching to the maximum in the midnight. Analysis on the gonotrophic cycle revealed that Ph. wui was an exophilic species and appeared nocturnally for feeding with preference to human blood. Natural infection with promastigotes was found in 4 sandflies, more in the field than the residential area. Resting places included the aperture on the wall of livestock sheds and in the caves. CONCLUSION: Ph. wui is the predominant species in Jiashi, with higher infection rate of natural promastigotes in the field and with two life generations annually.

[Field test of sandfly-catching by light traps and attractants].

Three kinds of light traps, attractants and their combination were used to collect sandflies in Andier township, Minfeng County of Xinjiang. The combined use of carbon dioxide and tungsten lamp showed better attraction effect to sandflies, also an easier way for the separation of insects collected.

[A newly identified endemic area of visceral leishmaniasis in Minfeng county of South Xinjiang I. epidemiological survey].

OBJECTIVE: To investigate the epidemiological status of visceral leishmaniasis in Minfeng county, a newly identified endemic area in south Xinjiang, China. METHODS: Based on a hint of possible existence of patients, a retrospective survey was carried out house by house in Andier Township of the county to find cases with suspected signs/symptoms of the disease in the past 20 years including those died. Meanwhile, a survey on current status was conducted, including physical examination(liver and spleen palpation) to those under 15 years-old, leishmanin skin test and rk39 immunochromatographic strip test for part of the residents. RESULTS: The investigation covered 313 local residents and revealed no case with present illness but 60 cases with a history of suspected signs/symptoms including 13 deaths, traced back as visceral leishmaniasis. Leishmanin skin test was performed in 171 people with a positive rate of 99.4% and 28 out of 29 suspected cases showed positive (96.6%). rk39 immunochromatographic strip test was conducted in 197 people with a positive rate of 10.2% (20/197) and 19.4% (6/31) in those with a history of suspected signs/symptoms. CONCLUSION: The epidemiological investigation indicates that the Andier Township of Minfeng County is an endemic area of visceral leishmaniasis.

[A newly identified endemic area of visceral leishmaniasis in Minfeng county of south Xinjiang II. Investigation on phlebotomine vectors].

OBJECTIVE: To investigate the transmitting phlebotomine sandfly in Minfeng County, a newly-identified endemic area of visceral leishmaniasis in the south of Talim Pendi of Xinjiang. METHODS: Sandflies were collected using routine methods in and around the Yatonggusi village of Andier Township. The sandflies were identified to get their composition. Sandfly density was calculated following an observation at a given spot and time-period, and their appearance was recorded at night-time and day-time. Sandflies were dissected to analyze the gonotrophic cycle and to find infection of promastigotes. RESULTS: Phlebotomus wui was identified as the transmitting vector of visceral leishmaniasis in Andier Township, which occupied 99.2% of the sandflies collected. The first and second ten-day period of June was the first peak of its seasonal distribution. Analysis of the gonotrophic cycle revealed that Ph. wui was an exophilic species and appeared nocturnally for feeding with preference to human blood. Natural infection with promastigotes was found in 2 sandflies. CONCLUSION: Phlebotomus wui is the transmitting vector for visceral leishmaniasis in the newly found endemic area of south Xinjiang.

[Preliminary test of phlebotomus surveillance by light-traps].

Different light-traps were tested in Wenxian of Gansu Province, including the light-traps without lamp and with glucose solution as attractant. Results showed that the light-traps attracted more mosquitoes and other insects than sandflies, and it became difficult to pick up the sandflies from gathering packet; the light-trap without lamp captured smaller amount of sandflies but much less other insects; glucose showed no significant effect in attracting sandflies. The existing light-traps are not so effective for Phlebotomus surveillance, and it is suggested that more effective attractants be tried.

[Asymptomatic Leishmania infection in human population of Wenxian County, Gansu Province].

OBJECTIVE: To analyze the status of Leishmania infantum asymptomatic infection in human population of a Kala-azar endemic area in Wenxian County, Gansu Province, and to evaluate the tests used. METHODS: Blood samples were tested by PCR using two pairs of primers, RV1-RV2 and K13A-K13B, for detecting Leishmania-specific DNA. ELISA and rK39-dipstick were used to detect Leishmania-specific antibodies. RESULTS: The positive rate of PCR, ELISA and rK39-dipstick was 30.9%(83/269). 24.2%(65/269) and 0 (0/269) respectively. CONCLUSION: The prevalence of asymptomatic infection of L. infantum in humans is high in the area. PCR test based on RV1-RV2 and K13A-K13B primer pairs is a sensitive and specific method for detecting the asymptomatic infection.

[Research progress on the resting habits of major sandflies and control strategy].

Based on the comprehensive studies in the past years, the authors reviewed important findings on biology, especially the resting habits, of the four major species of sandflies transmitting visceral leishmaniasis. The effective ways for sandfly control were also discussed.

[Ultrastructural study on pharyngeal armature of seven species of sandflies in china by scanning electron microscopy].

OBJECTIVE: To observe the ultrastructure of pharyngeal armature of 7 species of sandflies in China. METHODS: The pharyngeal armature of various sandflies were studied by scanning electron microscopy. RESULTS: The pharyngeal armature of sandfly consisted of pointed-teeth with various shape, number and arrangement among different species. CONCLUSION: Such differences may provide the morphological proof for identification of species.

[The effect of sandfly control on the transmission of visceral leishmaniasis].

OBJECTIVE: To observe the effect of Phlebotomus chinensis control including insecticide residual spraying in the habitats and bathing for dogs on the transmission of visceral leishmaniasis in Nanping of Sichuan Province. METHODS: Alpha-methrin with a dosage of 50 mg/m2 was sprayed in the wild caves and 2.5% deltamethrin wettable power at a concentration of 250 mg/L was applied for dog bathing in the villages. The density of sandflies in the natural caves was examined and data on the incidence of visceral leishmaniasis were collected from epidemiological survey following the sandfly control measures. RESULTS: The density of sandflies has been considerably reduced after the chemical spraying in caves, the important habitats of the sandflies. By both the cave spraying and bathing for dogs since 1993, the reported human cases of leishmaniasis also decreased. CONCLUSION: Measures for sandfly control including insecticide spraying in the habitats and bathing for dogs with insecticide solution can significantly reduce the sandfly density, and can contain the transmission of visceral leishmaniasis in the endemic area.