Characterization of a blood activated chitinolytic system in the midgut of the sand fly vectors Lutzomyia longipalpis and Phlebotomus papatasi.

We characterized a cDNA from Phlebotomus papatasi, PpChit1, which encodes a midgut specific chitinase and show the presence of a functional, blood-induced chitinolytic system in sand flies. PpChit1 is detected only in the midgut and is regulated by blood feeding. A recombinant protein (rPpChit1) produced in HEK 293-F cells exhibited a similar activity profile to that found in the native protein against several specific substrates, including an oligomeric glycol chitin and synthetic 4-methyl-umbelliferone labelled substrates. Western blotting showed that the native protein is recognized by mouse polyclonal antibodies against rPpChit1. Additionally, the rPpChit1 and the native chitinase displayed similar retention times in a HPLC size fractionation column. When added to rPpChit1 or to midgut lysates, PpChit1 sera reduced chitinolytic activity by 65-70%.

Rhesus monkey model for Leishmania major transmitted by Phlebotomus papatasi sandfly bites.

Leishmaniasis research needs a near-human model for investigations of natural infection processes, immunological responses and evaluation of treatments. Therefore, we developed a reproducible system using Leishmania major Yakimoff & Schokhor (Trypanosomatidae: Kinetoplastida), the cause of Old World zoonotic cutaneous leishmaniasis (ZCL), transmitted to rhesus monkeys Macaca mulatta (Zimmerman) (Primates: Cercopithecidae) by sandfly bites of experimentally infected Phlebotomus papatasi (Scopoli) (Diptera: Psychodidae). Eight monkeys of presumed Indian origin (Leishmania naive) were exposed to bites of female sandflies that had been infected with L. major by membrane-feeding on human blood seeded with amastigotes isolated from hamster footpad lesions. Infection rates of membrane-fed sandflies averaged > 85% seven days after the infective feed, with uniformly high numbers of promastigotes in the stomodaeal valve region of the sandfly gut. Nodules and ulcerating dermal lesions developed on 7/8 monkeys 2-4 weeks post-bite and persisted for 3-7 months. Monkeys also developed satellite lesions beyond the area of sandfly bites on the head, but not on the chest. Three re-challenged monkeys developed lesions that healed faster than lesions from their primary challenges. After infection, monkeys developed delayed type hypersensitivity (DTH) responses to a panel of Leishmania skin test antigens (LSTA) and, when tested by ELISA and IFA, showed significant post-infection antibody titres which typically rose for approximately 170 days and then gradually receded during the next 100 days following the first challenge. After the second challenge, antibody titres spiked higher within approximately 50 days and receded more rapidly. In contrast, four rhesus macaques of Chinese origin developed no lesions following infected sandfly bites, although they raised antibodies and LSTA reactions, indicating subclinical infection.

Laboratory transmission of Rift Valley fever virus by Phlebotomus duboscqi, Phlebotomus papatasi, Phlebotomus sergenti, and Sergentomyia schwetzi (Diptera: Psychodidae).

We examined the potential for Phlebotomus papatasi (Scopoli), Phlebotomus duboscqi (Neveu-Lemarie), Phlebotomus sergenti (Parrot), and Sergentomyia schwetzi (Adler, Theodor, & Parrot) to transmit Rift Valley fever (RVF) virus. After feeding on hamsters that had been inoculated with RVF virus, P. papatasi, P. sergenti, and S. schwetzi became infected and developed disseminated infections. All P. papatasi and P. duboscqi inoculated with RVF virus developed high-titer infections. In contrast, only 41% of the inoculated S. schwetzi contained detectable virus, and infected individuals contained significantly less virus than the two Phlebotomus species. Although 50% of the inoculated P. duboscqi transmitted RVF virus to hamsters, only 14% of P. papatasi and none of the S. schwetzi transmitted this virus. Additional studies are needed to determine the role of sand flies as vectors of RVF virus.

Phlebotomine sand fly (Diptera: Psychodidae) seasonal distribution and infection rates in a defined focus of Leishmania tropica.

A two-year study was conducted of phlebotomine sand fly fauna in a defined focus of Leishmania tropica. A total of 17,947 sand flies representing 10 species were collected from the location. Phlebotomus guggisbergi, a vector of L. tropica in Kenya, was the most prevalent species through the entire period, representing about 80% of the total catch. There was marked seasonal fluctuation in the populations of the three most common species, with highest population levels reached in December and lowest levels reached in July and August. Leishmania-like infections were encountered in 489 P. guggisbergi. No flagellate infections were observed in any other species of sand fly. Although infected P. guggisbergi were collected during each month of the year, the percent parous infected flies was highest (27.5%) during the November through January time period. These data show that the greatest risk of transmission to humans at this focus occurs during December, when the vector is prevalent and infections are common.

Random amplified polymorphic DNA (RAPD) analysis of Lutzomyia longipalpis laboratory populations.

The phlebotomine sand fly Lutzomyia longipalpis has been incriminated as a vector of American visceral leishmaniasis, caused by Leishmania chagasi. However, some evidence has been accumulated suggesting that it may exist in nature not as a single but as a species complex. Our goal was to compare four laboratory reference populations of L. longipalpis from distinct geographic regions at the molecular level by RAPD-PCR. We screened genomic DNA for polymorphic sites by PCR amplification with decamer single primers of arbitrary nucleotide sequences. One primer distinguished one population (Marajó Island, Pará State, Brazil) from the other three (Lapinha Cave, Minas Gerais State, Brazil; Melgar, Tolima Department, Colombia and Liberia, Guanacaste Province, Costa Rica). The population-specific and the conserved RAPD-PCR amplified fragments were cloned and shown to differ only in number of internal repeats.

Phlebotomine sand fly control using bait-fed adults to carry the larvicide Bacillus sphaericus to the larval habitat.

Sugar meals of plant origin are an important component of the sand fly diet. We show that sugar solution baits have potential as vehicles for phlebotomine sand fly control. In the laboratory, adult Phlebotomus duboscqi Neveu-Lemaire and Sergentomyia schwetzi (Adler, Theodor, and Parrot) that have consumed an aqueous sucrose solution containing Bacillus sphaericus Neide toxins and are subsequently eaten by larvae produce significant larval death (P < 0.01). In the field, when vegetation near animal burrows and eroded termite mounds was sprayed with sucrose solution with or without incorporation of the larval toxicant B. sphaericus, 40% of female sand flies fed in situ. Dispersing B. sphaericus-carrier sand flies caused significant larval mortality (P < 0.01) in resting and breeding sites in animal burrows 10-30 m from the sprayed vegetation for 2-12 wk posttreatment. Also, adult sand fly populations breeding and resting inside animal burrows were significantly reduced (P < 0.01) following direct application of the sucrose/B. sphaericus solution to the burrow entrances. This control effect lasted 4-10 wk post-treatment. The effect was not seen for sand fly populations breeding and resting inside eroded termite mounds. This approach may be useful for the application of biological control agents against phlebotomine sand flies in biotypes where larvae and adults use the same habitats.

Field evaluation of four repellents against Leptoconops americanus (Diptera: Ceratopogonidae) biting midges.

Four repellents, deet, AI3-37220, AI3-35765, and CIC-4, prepared as 12.5% ethanol solutions, were evaluated against biting midges on Stansbury Islands, UT. Leptoconops americanus Carter was the only species that was biting human volunteers during the study. This species bit primarily on the ears at rates up to 840 bites per hour. All four repellents significantly reduced the number of bites on treated volunteers. AI3-37220 consistently provided the longest period of protection, giving 97 and 74% protection at 4 and 8 h, respectively. In a direct statistical comparison, AI3-37220 significantly outperformed deet. CIC-4 and AI3-35765 were the least effective repellents, providing 45-47% protection 8 h after application.

Phlebotomine sandflies of Kenya (Diptera: Psychodidae). III. The identification and distribution of species of the subgenus Larroussius.

The six species of phlebotomine sandflies of the subgenus Larroussius recorded in Kenya are Phlebotomus aculeatus, P. elgonensis, P. guggisbergi, P. longipes, P. orientalis and P. pedifer. Five are proven vectors of leishmaniasis in that country or elsewhere. Males of all six can be identified by the morphology of the aedeagus or the number and position of the hairs on the inner surface of the coxite. Additional features separating some of the species are the sizes of the palpal and antennal segments. The females have usually been considered difficult or impossible to distinguish. A comparison of the base of the spermathecal ducts is made and it is shown that all six can be identified by this character alone. A map of Kenya is given, showing the presently known distribution of the six Larroussius species. Further surveys are necessary in parts of the country that have not been systematically surveyed.

Human cutaneous leishmaniasis caused by Leishmania donovani s.l. in Kenya.

Our laboratory is characterizing Leishmania stabilates and isolates from active leishmaniasis cases. Smears and cultures from aspirates made on different dates from a single lesion on the bridge of the nose of an 18 years old Kenyan male from Nyandarua District contained Leishmania. The isolates, NLB-271 and NLB-271-IA, were characterized by cellulose acetate electrophoresis (CAE) using 20 enzyme systems and by Southern analysis using 2 deoxyribonucleic acid (DNA) probes (pDK10 and pDK20) from a Dakar strain of L. major (MHOM/SN/00/DK1) and a third probe, p7-059 from L. infantum strain ITMAP-263. Digestion of the two Leishmania DNAs with endonucleases HindIII and PstI, followed by hybridization with the 3 probes, revealed DNA fragment banding patterns indistinguishable from those of the L. donovani species complex. The CAE isoenzyme profiles of these 2 Kenyan isolates were indistinguishable from those of Kenyan L. donovani strains we designated as zymodeme Z6. Excluding post-kala-azar dermal leishmaniasis, this constitutes the first human case of cutaneous leishmaniasis caused by L. donovani s.l. in Kenya. Previously, cutaneous leishmaniasis cases in Kenya have been due to L. aethiopica, L. major and L. tropica only.

Development and application of the polymerase chain reaction for the detection and identification of Leishmania parasites in clinical material.

Detection, diagnosis and identification of Leishmaniasis may be difficult owing to low numbers of parasites present in clinical samples. The PCR has improved the sensitivity and specificity of diagnosis of several infectious diseases. A leishmania specific PCR assay was developed based on the SSUrRNA genes which amplifies DNA of all Leishmania species. Point mutations occurring within the rRNA genes allow differentiation of the Leishmania complexes using primers constructed with the 3/ ends complementary to the specific point mutations present in the SSU rRNA genes of the Leishmania species. Biopsy material, blood, lesion impressions and blood spots on filter paper can be used in the assay. In a longitudinal study on the incidence rates of VL, subclinical cases and PKDL in an endemic region of Sudan, filter paper blood spots from proven and suspected VL patients, PKDL and control samples from an endemic region in Sudan are being taken. The blood spots were analyzed in the DAT and by PCR and results compared with clinical and parasitological data. The first results indicate that the PCR on blood spots is a simple and sensitive means of detecting active VL; in PKDL patients parasites are detectable in the skin.

Lutzomyia longipalpis is a species complex: genetic divergence and interspecific hybrid sterility among three populations.

The sand fly Lutzomyia longipalpis is the vector of Leishmania donovani chagasi in Latin America. An analysis of genetic variability at 27 enzyme coding loci among three laboratory populations of Lu. longipalpis revealed substantial genetic polymorphism. Levels of genetic distance between all pairwise comparisons of colonies were very high, and consistent with those previously reported among separate species in the genus Lutzomyia. Between 7% and 22% of the loci studied were diagnostic for any two of the colony populations. Experimental hybridization between colonies resulted in the production of sexually sterile male progeny. Our results provide strong evidence that Lu. longipalpis exists in nature as a complex of at least three distinct species. The possible effects of colonization on the genetic makeup of laboratory populations is considered in extending our results to natural populations.

Leishmania donovani parasites in the nasal secretions, tonsillopharyngeal mucosa, and urine centrifugates of visceral leishmaniasis patients in Kenya.

In the early 1930s, investigators of visceral leishmaniasis stated that Leishman-Donovan bodies are found in body fluids of kala-azar patients, for example, in urine, feces, semen, and nasal and pharyngeal secretions. Based on this finding, we investigated the diagnostic potential of nasal secretions, tonsillopharyngeal mucosal swabs, and urine centrifugates inoculated into Schneider's Drosophila Medium (containing antibiotics and antifungal agents) as well as with Giemsa-stained smears. Consequently, 64 randomly selected patients with visceral leishmaniasis from Kenya (59 who were splenic culture or Giemsa stain positive and five who were culture negative but Giemsa stain positive) were tested by three noninvasive methods. These tests were all performed before the patients were treated with Pentostam. Cultures of nasal and tonsillopharyngeal swabs and urine centrifugates produced 28 positive samples representing 24 patients (37.5%). Moreover, a set of 25 Giemsa-stained slide smears made from the nasal and tonsillopharyngeal mucosa of 25 patients with visceral leishmaniasis who had not tested positive in cultures produced nine positives. Therefore, the overall total of patients who tested positive by all of the above methods was 33 or 51.6%. The cryopreserved Leishmania isolates were characterized by cellulose acetate electrophoresis using 20 enzyme systems. The isoenzyme profiles produced by the parasites were represented in five different L. donovani s.l. zymodemes. Representatives of these isolates were also characterized by DNA Southern blotting analysis, which corroborated the isoenzyme results.

Biochemical characterization and zymodeme classification of Leishmania isolates from patients, vectors, and reservoir hosts in Kenya.

A total of 407 Leishmania and other Leishmania-like isolates obtained from patients, other vertebrates, sand fly vectors, and other arthropods from Kenya and other countries were characterized and compared with several World Health Organization and other well-characterized reference strains of Leishmania, Trypanosoma, Crithidia, Herpetomonas, and Leptomonas by cellulose acetate electrophoresis (CAE), using 20 enzyme systems. Analysis of the isoenzyme banding patterns (IBP) of the isolates generated isoenzyme profiles that were resolved as zymodemes and tabulated. Isolates that produced similar isoenzyme profiles in all 20 enzyme systems were placed into a particular Leishmania isoenzyme taxon, with the zymodeme designated numerically as Zn. A total of 66 zymodemes were recorded for the 407 isolates studied. To obviate the need to draw all 66 representative IBP for each of the 20 enzyme systems, the 66 zymodemes (Z1-Z66) were again placed into similarity groups represented by pattern number or Pn. This resulted in 23-50 IBP (Pn) per enzyme system. The highest number of IBP scored was for malate dehydrogenase (MDH) (P1-50) and the lowest score was for glucose-6-phosphate isomerase (GPI) (P1-23). From these different isoenzyme profiles or zymodemes, IBP of 14 (MDH, GPI, nucleoside hydrolase, phosphoglucomutase, malic enzyme, isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, mannose-6-phosphate isomerase, 6-phosphogluconate dehydrogenase, glutamate oxaloacetate transferase/aspartate aminotransferase, glutathione reductase, superoxide dismutase, fumarase, and glyceraldehyde-3-phosphate dehydrogenase) of the 20 enzyme systems were selected for computer-calculated numerical taxonomy. Consistent individual isoenzyme bands with similar relative mobilities of the 14 enzyme systems were scored into groups (allelomorphs, allozymes, or electromorphs) and used in cluster analysis. For each pattern in every profile, the presence of a consistent band was entered as 1 and its absence as 0. A total of 419 allozyme characters (variables) were scored for the 14 enzyme systems. Lastly, all different zymodemes sharing a particular IBP (Pn) within an enzyme system were counted and the total number was shown as a zymodeme frequency (Zf). Final analysis of the CAE isoenzyme profiles and cluster-dendrograms resulted in the identification of several potentially new species and subspecies of Leishmania and other Leishmania-like isolates from patients, sand flies, and animal reservoir hosts collected from Kenya and other locations in Africa. Zymodeme analysis of the Kenyan visceral and cutaneous leishmaniasis isolates resulted in the identification of 11 subpopulations of the L. donovani species complex and six subpopulations of the L. tropica species complex endemic to different geographic areas of Kenya.

Identification of phlebotomine sandfly bloodmeals from Baringo District, Kenya, by direct enzyme-linked immunosorbent assay (ELISA).

Direct enzyme-linked immunosorbent assay (ELISA) was used to identify the sources of bloodmeals in phlebotomine sandflies from Baringo District, Rift Valley Province, Kenya. Some bloodmeals had been stored for over 4 years before being analysed. Among 356 sandflies identified, 62.9% were Phlebotomus martini, 14.8% Sergentomyia antennatus, 10% S.schwetzi, 6% S.clydei, 1.9% S.adleri, 1.6% P.duboscqi, 1.4% S.africanus and 0.8% S.bedfordi. Out of 224 P.martini bloodmeals, host source was identified for 69. The order of host preference for P.martini was: goat 28.5%, rabbit 22.7%, human 8.9% and others 8.9%. Evidence of mixed feeding was shown by four species comprising sixteen specimens, twelve of which were P.martini. The most effective methods for trapping bloodfed P. martini were sticky paper traps in termite hills, followed by light-traps. Of the 224 P.martini trapped, 58.9% were collected with traps in termite hills, and 22.7% with light traps. Roles of the three most popular hosts for P.martini should be investigated to ascertain whether they act as reservoirs in the transmission of Leishmania donovani causing visceral leishmaniasis in Kenya.

A new rural focus of cutaneous leishmaniasis caused by Leishmania tropica in Kenya.

We have identified a new rural focus of cutaneous leishmaniasis caused by Leishmania tropica in Muruku sublocation, Salama location, Laikipia district, Rift Valley province, Kenya. Based on a few available case histories, previous reports of L. tropica in Kenya indicated a tentative geographical distribution. Recently 6 indigenous Kenyans from the new focus, who had never travelled outside Kenya, developed cutaneous lesions on the face and/or extremities found to contain Leishmania by culture and smear. Most of the patients manifested the typical 'urban' dry sore which grew slowly into a nodule measuring 2 x 1 cm to 9.5 x 3 cm, and after some months formed a central crust surrounded by small satellite papules. After treatment with Pentostam (sodium stibogluconate), about 40% of the sores failed to heal completely, either scarring centrally with fulminating papules at the edges and spreading peripherally, or healing but then recrudescing at the edge of the scar. Stationary-phase promastigotes from culture isolates were analysed by cellulose acetate electrophoresis. Isoenzyme profiles of 6 isolates were compared with those of World Health Organization reference strains using 12 enzyme loci; they were indistinguishable from those of 2 L. tropica reference strains. All 6 case sites lay within a radius of 4 km. Several other suspected cases from the same area are being investigated.

Epidemiologic investigation of an outbreak of cutaneous leishmaniasis in a defined geographic focus of transmission.

An outbreak of cutaneous leishmaniasis occurred in a unit of 608 Puerto Rican national guardsmen conducting jungle warfare training in the Panama Canal Area in July 1984. An epidemiologic investigation of reported nonhealing, ulcerating skin lesions was conducted among 540 (89%) unit members in November and December 1984. Fifteen (88%) of 17 individuals with chronic, ulcerating skin lesions were confirmed as cases of cutaneous leishmaniasis by culture or histopathology. Twelve cases yielded positive Leishmania cultures, identified as L. braziliensis panamensis by cellulose acetate electrophoresis. Evaluation of different diagnostic techniques revealed that direct examination of tissues by Giemsa-stained histological examination was the most sensitive test (87% sensitivity), with an indirect immunofluorescent antibody test being rather insensitive (67%). All but one of the confirmed cases operated in small units that trained and slept overnight at a mortar firing site for a period of three days, yielding a site-specific attack rate of 22% (14 of 64). This contrasted with a much lower attack rate of 0.2% (1 of 476), experienced by unit members who trained at other locations during the same time frame (P less than 0.001). The median incubation period calculated from day of arrival at the mortar firing site was 17 days (range 2-78) for the 15 confirmed cases. Available personal protection methods, such as the use of insect repellents, were not appropriately implemented by unit personnel and thus, were not found to effectively protect against Leishmania infection. This is the largest reported outbreak of cutaneous leishmaniasis in military personnel associated with a single geographic focus of infection and contrasts with the usual sporadic disease experience in Panama.

Stage-specific adhesion of Leishmania promastigotes to the sandfly midgut.

Although leishmaniasis is transmitted to humans almost exclusively by the bite of infected phlebotomine sandflies, little is known about the molecules controlling the survival and development of Leishmania parasites in their insect vectors. Adhesion of Leishmania promastigotes to the midgut epithelial cells of the sandfly was found to be an inherent property of noninfective-stage promastigotes, which was lost during their transformation to metacyclic forms, thus permitting the selective release of infective-stage parasites for subsequent transmission by bite. Midgut attachment and release was found to be controlled by specific developmental modifications in terminally exposed saccharides on lipophosphoglycan, the major surface molecule on Leishmania promastigotes.

Identification of Phlebotomine Sandfly Bloodmeals from Baringo District; Kenya; by Direct Enzyme-Linked Immunosorbent Assay (ELISA)

Direct enzyme-linked immunosorbent assay (ELISA) was used to identify the sources of 356 phlebotomine sandfly bloodmeals from Baringo District; Rift Valley Province; Kenya. Some bloodmeals had been stored for over 4 years before being analysed. Of the 356 sandflies; 62.9 were phlebotomus martini; 14.8 Sergentomyia antennatus; 10.0 S. schwetzi; 6.0 S. clydei; 1.9 S. adleri; 1.6 P. duboscqi; 1.4 S. africanus; and 0.8 S. bedfordi. Out of 224 P. martini bloodmeals; host source was identified for 69. The order of host prefernce for P. martini was: goat 28.5; rabbit 22.7 human 8.9 and other 8.9. Evidence of mixed feeding was shown by 16 sandflies comprising 4 species; 12 of these were P. martini. The most effective methods for trapping bloodfed P. martini; were sticky paper traps in termite hills; followed by light-traps. Of the 224 P. martini trapped; 58.9 were collected with paper traps in termite hills; and 22.7 with light traps. The role played by the 3 most popular hosts for P. martini should be investigated to ascertain whether they act as reservoirs in the transmission of visceral leishmaniasis in Kenya

Recent advances in laboratory mass rearing of phlebotomine sand flies.

Recent technical and procedural advances in mass rearing of sand flies have resulted in larger, healthier, and less labor-intensive colonies. We now maintain closed colonies of Phlebotomus papatasi, P. duboscqi, P. argentipes, and Lutzomyia longipalpis which produce up to 1,000 females per week, in excess of colony-maintenance requirements, for use in research. Advances include larval food preparation in acrylic-plastic incubator cabinets, strict regulation of food quantity and moisture in 500-ml plaster-lined rearing jars, use of large plaster-lined adult holding/mating cages and vacuum-powered aspirators for trauma-free handling of adults.