Biomedical subjects

S Kamhawi

Publications and source records attributed to S Kamhawi.

At least 19 recordsLinked to original sources

PubMed2005

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%.

Amino Acid Sequence↗

PubMed2003

Cloning and characterization of trypsin- and chymotrypsin-like proteases from the midgut of the sand fly vector Phlebotomus papatasi.

Trypsin and chymotrypsin serine proteases are the main digestive proteases in Diptera midguts and are also involved in many aspects of the vector-parasite relationship. In sand flies, these proteases have been shown to be a potential barrier to Leishmania growth and development within the midgut. Here we describe the sequence and partial characterization of six Phlebotomus papatasi midgut serine proteases: two chymotrypsin-like (Ppchym1 and Ppchym2) and four trypsin-like (Pptryp1-Pptryp4). All six enzymes show structural features typical to each type, including the histidine, aspartic acid, and serine (H/D/S) catalytic triad, six conserved cysteine residues, and other amino acid residues involved in substrate specificity. They also show a high degree of homology (40-60% identical residues) with their counterparts from other insect vectors, such as Anopheles gambiae and Aedes aegypti. The mRNA expression profiles of these six proteases vary considerably: two trypsin-like proteases (Pptryp1 and Pptryp2) are downregulated and one (Pptryp4) upregulated upon blood feeding. The two chymotrypsin-like enzymes display expression behavior similar to that of the early and late trypsins from Ae. aegypti.

Amino Acid Sequence↗

PubMed2001

The role of interleukin (IL)-10 in the persistence of Leishmania major in the skin after healing and the therapeutic potential of anti-IL-10 receptor antibody for sterile cure.

Some pathogens (e.g., Mycobacterium tuberculosis, Toxoplasma gondii, Leishmania spp) have been shown to persist in their host after clinical cure, establishing the risk of disease reactivation. We analyzed the conditions necessary for the long term maintenance of Leishmania major in genetically resistant C57BL/6 mice after spontaneous healing of their dermal lesions. Interleukin (IL)-10 was found to play an essential role in parasite persistence as sterile cure was achieved in IL-10-deficient and IL-4/IL-10 double-deficient mice. The requirement for IL-10 in establishing latency associated with natural infection was confirmed in IL-10-deficient mice challenged by bite of infected sand flies. The host-parasite equilibrium was maintained by CD4+ and CD8+ T cells which were each able to release IL-10 or interferon (IFN)-gamma, and were found to accumulate in chronic sites of infection, including the skin and draining lymph node. A high frequency of the dermal CD4+ T cells released both IL-10 and IFN-gamma. Wild-type mice treated transiently during the chronic phase with anti-IL-10 receptor antibodies achieved sterile cure, suggesting a novel therapeutic approach to eliminate latency, infection reservoirs, and the risk of reactivation disease.

Animals↗

PubMed2001

Toward a defined anti-Leishmania vaccine targeting vector antigens: characterization of a protective salivary protein.

Leishmania parasites are transmitted to their vertebrate hosts by infected phlebotomine sand fly bites. Sand fly saliva is known to enhance Leishmania infection, while immunity to the saliva protects against infection as determined by coinoculation of parasites with vector salivary gland homogenates (SGHs) or by infected sand fly bites (Kamhawi, S., Y. Belkaid, G. Modi, E. Rowton, and D. Sacks. 2000. Science. 290:1351-1354). We have now characterized nine salivary proteins of Phlebotomus papatasi, the vector of Leishmania major. One of these salivary proteins, extracted from SDS gels and having an apparent mol wt of 15 kD, was able to protect vaccinated mice challenged with parasites plus SGH. A DNA vaccine containing the cDNA for the predominant 15-kD protein (named SP15) provided this same protection. Protection lasted at least 3 mo after immunization. The vaccine produced both intense humoral and delayed-type hypersensitivity (DTH) reactions. B cell-deficient mice immunized with the SP15 plasmid vaccine successfully controlled Leishmania infection when injected with Leishmania plus SGH. These results indicate that DTH response against saliva provides most or all of the protective effects of this vaccine and that salivary gland proteins or their cDNAs are viable vaccine targets against leishmaniasis.

Amino Acid Sequence↗

PubMed2001

The potency and durability of DNA- and protein-based vaccines against Leishmania major evaluated using low-dose, intradermal challenge.

DNA- and protein- based vaccines against cutaneous leishmaniasis due to Leishmania major were evaluated using a challenge model that more closely reproduces the pathology and immunity associated with sand fly-transmitted infection. C57BL/6 mice were vaccinated s.c. with a mixture of plasmid DNAs encoding the Leishmania Ags LACK, LmSTI1, and TSA (AgDNA), or with autoclaved L. major promastigotes (ALM) plus rIL-12, and the mice were challenged by inoculation of 100 metacyclic promastigotes in the ear dermis. When challenged at 2 wk postvaccination, mice receiving AgDNA or ALM/rIL-12 were completely protected against the development of dermal lesions, and both groups had a 100-fold reduction in peak dermal parasite loads compared with controls. When challenged at 12 wk, mice vaccinated with ALM/rIL-12 maintained partial protection against dermal lesions and their parasite loads were no longer significantly reduced, whereas the mice vaccinated with AgDNA remained completely protected and had a 1000-fold reduction in dermal parasite loads. Mice vaccinated with AgDNA also harbored few, if any, parasites in the skin during the chronic phase, and their ability to transmit L. major to vector sand flies was completely abrogated. The durable protection in mice vaccinated with AgDNA was associated with the recruitment of both CD8(+) and CD4(+) T cells to the site of intradermal challenge and with IFN-gamma production by CD8(+) T cells in lymph nodes draining the challenge site. These data suggest that under conditions of natural challenge, DNA vaccination has the capacity to confer complete protection against cutaneous leishmaniasis and to prevent the establishment of infection reservoirs.

Animals↗

PubMed2001

Molecular aspects of parasite-vector and vector-host interactions in leishmaniasis.

Leishmania-sand fly interactions are reviewed in the context of the potential barriers to the complete development of the parasite that exist within the midgut environment of phlebotomine flies and the molecular adaptations that the parasite has evolved that permit the development of transmissible infections to proceed. Cell surface and secreted phosphoglycans protect the parasite from the proteolytic activities of the blood-fed midgut, mediate attachment to the gut wall in order to maintain infection during excretion of the bloodmeal, and contribute to the formation of a biological plug in the anterior gut that may promote transmission by bite. The importance of vector saliva in modulating the host response to transmitted parasites is also reviewed.

Animals↗

PubMed2000

Protection against cutaneous leishmaniasis resulting from bites of uninfected sand flies.

Despite the fact that Leishmania are transmitted exclusively by sand flies, none of the experimental models of leishmaniasis have established infection via sand fly bites. Here we describe a reproducible murine model of Leishmania major infection transmitted by Phlebotomus papatasi. Prior exposure of mice to bites of uninfected sand flies conferred powerful protection against Leishmania major that was associated with a strong delayed-type hypersensitivity response and with interferon-gamma production at the site of parasite delivery. These results have important implications for the epidemiology of cutaneous leishmaniasis and suggest a vaccination strategy against this and possibly other vector-borne diseases.

Animals↗

PubMed2000

Delayed-type hypersensitivity to Phlebotomus papatasi sand fly bite: An adaptive response induced by the fly?

The saliva of bloodsucking arthropods contains a large array of pharmacologically active compounds that assist hematophagy. Arthropod saliva is also responsible for causing uncomfortable allergic responses in its vertebrate hosts. In this article, we investigate whether the sand fly Phlebotomus papatasi, known to produce a strong delayed-type hypersensitivity (DTH) in humans, could benefit from, and possibly adaptively induce, this response in their vertebrate hosts. In this study, we show that flies fed on humans to completion nearly twice as fast in DTH sites as compared with normal skin sites. DTH sites had significantly larger blood flow as measured by the laser Doppler method. Sand flies feeding at sites in mouse ears that had a DTH response also fed faster than at normal sites. We conclude that in the case of P. papatasi, and possibly other arthropods such as fleas and bed bugs, the strong saliva-induced DTH response may reflect an adaptation of the fly to manipulate host immunity for the insect's own advantage.

Adaptation, Physiological↗

PubMed2000

The biological and immunomodulatory properties of sand fly saliva and its role in the establishment of Leishmania infections.

Sand fly saliva contains a rich array of pharmacologically active compounds whose primary function is to prevent the hemostatic mechanisms of the host. Several studies have ascribed immunosuppressive properties to sand fly saliva as well as an exacerbative effect on Leishmania infectivity for their mammalian hosts. This review provides a comprehensive account of sand fly salivary components, the immunomodulatory properties exhibited by some of its molecules, and describes the findings concerning the influence of saliva on Leishmania infections. The potential use of saliva as part of an anti-Leishmania vaccine for the mammalian host is also addressed.

Animals↗

PubMed2000

The vectorial competence of Phlebotomus sergenti is specific for Leishmania tropica and is controlled by species-specific, lipophosphoglycan-mediated midgut attachment.

The vectorial competence of Phlebotomus sergenti for 3 Old World species of Leishmania, L. tropica, L. major and L. donovani, was investigated in vivo and by in vitro midgut binding assays using living promastigotes and purified lipophosphoglycan (LPG). P. sergenti consistently showed a high specificity for L. tropica strains, which were able to develop mature, potentially transmissible infections. The loss of infection with L. major and L. donovani correlated with the excretion of the digested bloodmeal. These strains were able to produce sustained infections in the midguts of their appropriate vectors, P. papatasi and P. argentipes, respectively. In in vitro binding assays, a significantly higher number of L. tropica procyclic promastigotes attached to the midgut lining of P. sergenti, compared to those of L. major and L. donovani (P < 0.05). The prediction that the species specificity of midgut attachment is controlled by polymorphic structures on the parasite LPG was supported by the finding that P. sergenti midguts were intensely stained following incubation with purified phosphoglycan (PG) from L. tropica compared with PGs from L. major or L. donovani. The results provide further evidence that LPG structural polymorphisms are driven by the species diversity of molecules present on the sandfly midgut that function as parasite attachment sites.

Animals↗

PubMed1998

Development of a natural model of cutaneous leishmaniasis: powerful effects of vector saliva and saliva preexposure on the long-term outcome of Leishmania major infection in the mouse ear dermis.

We have developed a model of cutaneous leishmaniasis due to Leishmania major that seeks to mimic the natural conditions of infection. 1,000 metacyclic promastigotes were coinoculated with a salivary gland sonicate (SGS) obtained from a natural vector, Phlebotomus papatasii, into the ear dermis of naive mice or of mice preexposed to SGS. The studies reveal a dramatic exacerbating effect of SGS on lesion development in the dermal site, and a complete abrogation of this effect in mice preexposed to salivary components. In both BALB/c and C57Bl/6 (B/6) mice, the dermal lesions appeared earlier, were more destructive, and contained greater numbers of parasites after infection in the presence of SGS. Furthermore, coinoculation of SGS converted B/6 mice into a nonhealing phenotype. No effect of SGS was seen in either IL-4- deficient or in SCID mice. Disease exacerbation in both BALB/c and B/6 mice was associated with an early (6 h) increase in the frequency of epidermal cells producing type 2 cytokines. SGS did not elicit type 2 cytokines in the epidermis of mice previously injected with SGS. These mice made antisaliva antibodies that were able to neutralize the ability of SGS to enhance infection and to elicit IL-4 and IL-5 responses in the epidermis. These results are the first to suggest that for individuals at risk of vector-borne infections, history of exposure to vector saliva might influence the outcome of exposure to transmitted parasites.

Animals↗

PubMed1998

Novel antigens for neurocysticercosis: simple method for preparation and evaluation for serodiagnosis.

Neurocysticercosis (NCC), which is caused by infection with the larval stage of the pork tapeworm (Taenia solium), is now recognized as a major cause of neurologic diseases in countries where the infection is endemic. Migration of persons from these countries is resulting in diagnosis and local transmission in nonendemic countries at increasing rates. In the present study, immunoblotting and an ELISA were carried out using antigens of T. solium cysticerci fractionated by isoelectric focusing and serum samples from patients with NCC, alveolar (AE) or cystic echinococcosis (CE), and other diseases. Immunoblot analysis revealed antigens fractionated by isoelectric focusing (pH 9.2-9.6) either from cyst fluid of T. solium cysticerci or from intact cysts had unique components (glycoproteins) highly specific and sensitive for detection of NCC exclusively. All confirmed NCC serum samples (53 of 53) recognized at least three major bands of 10-26-kD of fractions with pH 9.2-9.6 from either intact cysts or cyst fluid. These bands were not recognized by sera from patients with other parasitic diseases including AE (0 of 34), CE (0 of 36), or other heterologous parasitoses (0 of 77), patients with hepatoma (0 of 19) or sarcoidosis (0 of 11), or sera from healthy controls (0 of 29). The ELISA using the antigens showed the same sensitivity and specificity for differentiation of NCC (53 of 53) from other diseases (0 of 107) or healthy individuals (0 of 29). Both immunoblotting and the ELISA using the fractionated antigens readily differentiated all NCC from AE or CE in a blind test of 29 serum samples of persons with NCC, CE, and AE. Antigens fractionated from cyst fluid of T. solium cysticerci by a simple, single-step isoelectric focusing (pH 9.2-9.6) are highly specific and sensitive for differential serodiagnosis of NCC in immunoblotting and/or an ELISA.

Animals↗

PubMed1995

A retrospective study of human cystic echinococcosis in Jordan.

Some 676 human cases of cystic echinococcosis (CE) were recorded from 18 major hospitals in Jordan from January 1985 to October 1993. The number and origins of the cases indicate that CE is an endemic and widespread disease in Jordan. Operations for the extraction of hydatid cysts represented 0.1% of all surgical operations carried out in the surveyed hospitals during the study period (excluding Caesarean sections). The mean annual surgical incidence of CE was estimated to be 0.5-8.2 per 100,000 population, depending on the governorate studied, with an overall mean of 2.9 per 100,000. Incidence was higher in the more rural eastern and south-western governorates than elsewhere, and more cases fell in the 21-30-year age group than in any other. Many more of the cases were female than male (443 v. 233; P < 0.001). The liver was the most common organ infected (54.5% of cases), followed by the lungs (12.1%), and multiple hydatidosis usually involved the liver.

Adolescent↗

PubMed1995

Prevalence of hydatid cysts in livestock from five regions of Jordan.

When the prevalences of cystic echinococcosis in indigenous sheep, goats, cattle and camels from five regions of Jordan were investigated, from March to December 1992, they were found to be 12.9%, 12.7%, 0.9% and 11%, respectively. They were substantially higher in sheep from Karak (27.6%) and in cattle from central Jordan (18.0% in Amman and 14.3% in Sahab) than in the same animals in other regions. Age-intensity data indicated that the parasite population is endemic in sheep and cattle and hyperendemic in goats. Infection rate increased steadily with age in sheep, but became constant in goats and cattle when they were about 2 years of age. The most common locations of cysts were the liver in sheep and goats and the lungs in cattle. Co-infection of the liver and lungs was common in sheep and cattle. Although the majority of the sheep, cattle and goats had 1-10 cysts, 20.4% of the sheep and 22.2% of the cattle had 11-50 and 11-30 cysts, respectively. Although 38.1% of the cysts in sheep were fertile, only 8.7% of the cattle cysts and 4.5% of the goat cysts were in this condition. The overall mean number of protoscolices/sheep cyst was 2.7 x 10(3); although the liver cysts had more protoscolices than the lung cysts (3.2 x 10(3) v. 1.9 x 10(3)/cyst), more of the lung cysts were viable (71.1% v. 62.3%). Some 0.2% of 13,436 sheep and 6.1% of 786 cattle imported live into Jordan were infected with hydatid cysts; 16.3% of the sheep cysts (61.4% viable) and 9.6% of the cattle cysts (76.1% viable) were fertile.

Age Distribution↗

PubMed1995

Species composition of sand flies and population dynamics of Phlebotomus papatasi (Diptera: Psychodidae) in the southern Jordan Valley, an endemic focus of cutaneous leishmaniasis.

The species composition of sand flies and the seasonality of Phlebotomus papatasi Scopoli were studied in the southern Jordan Valley from May to November 1992 using CDC light traps. Eleven species of sand flies were recorded, including P. kazeruni Theodor & Mesghali and P. tobbi Adler & Theodor, which are new records for the study area, and Sergentomyia squamipleuris Newstead, which is reported for the first time from Jordan. P. papatasi was the most abundant Phlebotomus species collected from domestic habitats as well as Psammomys obesus Cretzschmar burrows, comprising 89.4 and 99.5% of the total Phlebotomus catches, respectively. The catch of P. papatasi in CDC light traps was compared among domestic habitats, P. obesus burrows in an agriculturally modified semiarid rural habitat, and P. obesus burrows in a natural semiarid rural habitat. Peak P. papatasi abundance occurred in September and October and then declined sharply by late November. The abundance and temporal association of P. papatasi activity with the prevalence of cutaneous leishmaniasis in the study area pointed to the significance of this sand fly in the transmission of the parasite.

Animals↗

PubMed1995

Incrimination of Phlebotomus papatasi as vector of Leishmania major in the southern Jordan Valley.

The status of sandflies as vectors of cutaneous leishmaniasis in the southern Jordan Valley was investigated during 1992. Sandflies were collected from domestic habitats and from burrows of Psammomys obesus. Of 686 Phlebotomus papatasi females collected from burrows, fourteen harboured promastigotes in their guts. On the other hand, none of 1446 P.papatasi females collected from domestic habitats were found infected. The highest infection rate (5.5%) was recorded in November at the end of the sandfly season. Six leishmanial stocks isolated from P.papatasi females were typed by cellulose acetate electrophoresis using the six enzymes G6PDH, 6PGDH, PGI, PGM, FK and ME. Five of the leishmanial stocks were identical to a Leishmania major reference strain (MHOM/SU/73/5-ASKH). The sixth isolate was a 6PGDH variant of L.major. These findings present the first direct evidence of the role of P.papatasi as a vector of L.major in Jordan.

Animals↗

PubMed1991

Urbanization--how does it affect the behaviour of sandflies?

The effect of building activities on the abundance of sandflies was investigated in Jordan. A total of 3442 sandflies were collected. The largest collections were made from natural habitats, uninhabited and inhabited houses. Collections from the latter two often included a larger number of Phlebotomus species. It was evident from this study that sandfly populations are able to recover to, and often exceed their original natural densities in man-made artificial habitats.

Animals↗

PubMed1991

The behaviour and dispersal of sandflies in Ras el Naqb, south Jordan with particular emphasis on Phlebotomus kazeruni.

The behaviour and dispersal of sandflies from an enclosed cave were investigated during the summer of 1988 in Ras el Naqb by the mark-release-recapture technique. Nine species of sandflies were reported during this study including 5 Phlebotomus and 4 Sergentomyia species. P. sergenti, P. alexandri, S. adleri/S. clydei and S. taizi were reported for the first time from Jordan. P. kazeruni was the most abundant sandfly species inside the cave. The maximum distance travelled by a single P. kazeruni was 340m. However, the majority were recaptured within 10m of the cave. It seems likely that an independent "population" of sandflies which breeds inside the cave is developing.

Animals↗