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R B Tesh

Publications and source records attributed to R B Tesh.

At least 55 records · Page 3Linked to original sources
PubMed1995

Control of zoonotic visceral leishmaniasis: is it time to change strategies?

Zoonotic visceral leishmaniasis (ZVL) is an important emerging parasitic disease. This article reviews the recommended control methods for the disease and concludes that they have only been partially effective. The continued endemicity of ZVL, its recent appearance in urban areas of Latin America, and its increasing importance as an opportunistic infection among persons infected with human immunodeficiency virus indicate that present control methods for the disease are ineffective and that new control strategies are needed. Prevention of the disease in dogs appears to be the best approach for interrupting the domestic cycle of ZVL. The most feasible approach would seem to be a canine vaccine that protects dogs from developing parasitemia and from becoming peridomestic reservoirs of the parasite.

AIDS-Related Opportunistic Infections↗
PubMed1994

Replacement of the natural Wolbachia symbiont of Drosophila simulans with a mosquito counterpart.

Inherited rickettsial symbionts of the genus Wolbachia occur commonly in arthropods and have been implicated in the expression of parthenogenesis, feminization and cytoplasmic incompatibility Wolbachia from the Asian tiger mosquito, Aedes albopictus, to replace the natural infection of Drosophila simulans by means of embryonic microinjection techniques. The transferred Wolbachia infection behaves like a natural Drosophila infection with regard to its inheritance, cytoskeleton interactions and ability to induce incompatibility when crossed with uninfected flies. The transinfected flies are bidirectionally incompatible with all other naturally infected strains of Drosophila simulans, however, and as such represent a unique crossing type. The successful transfer of this symbiont between distantly related hosts suggests that it may be possible to introduce this agent experimentally into arthropod species of medical and agricultural importance in order to manipulate natural populations genetically.

Aedes↗
PubMed1994

Histologic detection of multiple blood meals in Phlebotomus duboscqi (Diptera: Psychodidae).

A histologic technique was used to detect multiple hamster blood meals taken by Phlebotomus duboscqi Neveu-Lemaire during a 5-d period. Forty-eight flies were fed two or three blood meals separated by 48, 72, or 120 h and sampled immediately; multiple meals were detected in 27 flies (56%). Double meals separated by 72 h within a single gonotrophic cycle were documented in 11/19 (58%) flies; double meals separated by 120 h were detected in only 4/17 (24%) flies. Triple blood meals taken at 0, 72, and 120 h were detected in 5/12 (42%) flies; all of these flies contained the second and third meals. Early blood meals were detected clearly within later blood meals as a delimited body of dark digested blood, heme (sometimes also with pink undigested blood), the presence of an associated pale pink-staining peritrophic plug, the presence and appearance of the peritrophic membrane surrounding the meals, and a physical space between meals; the first two characteristics were the most important. Development of the ovarian follicles including apparent dilatations was also observable using this histologic technique. The results of this study indicate that the rate of multiple feeding can be determined using histology. The technique would be useful in evaluating the blood feeding frequency of field-caught sand flies in endemic areas of leishmaniasis, bartonellosis, and phleboviruses.

Animal Feed↗
PubMed1994

Description of Guanarito virus (Arenaviridae: Arenavirus), the etiologic agent of Venezuelan hemorrhagic fever.

This paper characterizes Guanarito virus, the etiologic agent of Venezuelan hemorrhagic fever. Based on its morphology and antigenic properties, Guanarito virus appears to be a new member of the Tacaribe complex of the genus Arenavirus, family Arenaviridae. Complement fixation and indirect fluorescent antibody tests showed that Guanarito virus and its antiserum are broadly cross-reactive with other members of the Tacaribe complex, but it can be differentiated from other members of the complex by neutralization test. Guanarito virus causes mortality in suckling mice and adult guinea pigs, but not in adult mice. Inoculated rhesus monkeys developed viremia and became ill; however, they subsequently recovered and responded with production of antibody. To date, all isolates of Guanarito virus have come from sick persons or wild rodents living within a single geographic focus in the central plains of Venezuela.

Adult↗
PubMed1994

Evidence of sexual reproduction in the protozoan parasite Leishmania (Kinetoplastida: Trypanosomatidae).

Parasitic protozoa of the genus Leishmania (Kinetoplastida: Trypanosomatidae) are generally thought to multiply by binary fission; however, data from quantitative microspectrophotometry indicate that nuclear fusion or sexual reproduction takes place in the intracellular amastigote form. Among several different Leishmania species, the mean +/- SD nuclear DNA content of all promastigotes (extracellular form) and of some amastigotes (intracellular form) in macrophages was 0.098 +/- 0.032 relative units; in contrast, other amastigotes within the same macrophage had a mean +/- SD nuclear DNA content of 0.219 +/- 0.050. The latter population of amastigotes are apparently produced when the nuclei of a pair of 0.098 amastigotes fuse. These 0.219 amastigotes later go through what is probably the typical meiotic cycle to reform the 0.098 condition we observed among promastigotes. The demonstration of sexual reproduction in Leishmania has important implications for the future direction of research on this medically important parasite.

Animals↗
PubMed1993

Coltiviruses isolated from mosquitoes collected in Indonesia.

Viruses with genomes consisting of 12 segments of double-stranded (ds) RNA were isolated from mosquito pools collected in Indonesia in 1980 and 1981. The genome segments of 11 virus isolates exhibited two distinct electrophoretic patterns in agarose gels, and the viruses probably represent distinct groups of Coltiviruses. Ten of the 11 virus isolates produced recognizably similar PAGE profiles of two groups of 6 segments (6-6) with 3 distinct profile variants, and the remaining virus isolate displayed a unique 6-5-1 profile. These profiles were distinct from that of Colorado tick fever (CTF) virus RNA. The genetic relatedness of the isolates was examined by RNA-RNA hybridization. The viruses with a 6-6 profile were closely related in the majority of their segments, with segments 7, 11, and 12 being variant; and segment 9 the most divergent. The segments of the virus with the unique PAGE profile (6-5-1) did not cross-hybridize with any of the other viruses. Similarly, RNA from virus isolates from Indonesian did not cross-hybridize with the segments of CTF virus. These data indicate that two additional genotypes are present in the Coltivirus genus.

Animals↗
PubMed1993

Modification of arthropod vector competence via symbiotic bacteria.

Some of the world's most devastating diseases are transmitted by arthropod vectors. Attempts to control these arthropods are currently being challenged by the widespread appearance of insecticide resistance. It is therefore desirable to develop alternative strategies to complement existing methods of vector control. In this review, Charles Beard, Scott O'Neill, Robert Tesh, Frank Richards and Serap Aksoy present an approach for introducing foreign genes into insects in order to confer refractoriness to vector populations, ie. the inability to transmit disease-causing agents. This approach aims to express foreign anti-parasitic or anti-viral gene products in symbiotic bacteria harbored by insects. The potential use of naturally occurring symbiont-based mechanisms in the spread of such refractory phenotypes is also discussed.

Journal Article↗
PubMed1993

Formation and composition of the peritrophic membrane in the sand fly, Phlebotomus perniciosus (Diptera: Psychodidae).

The secretion, morphology, and chemical composition of the peritrophic membrane was studied in the sand fly, Phlebotomus perniciosus Newstead. The membrane was secreted from the entire midgut epithelium. An electron-dense fine granular secretion, possibly chitin, was present along the length of the microvilli immediately until 24 h after feeding. From 12-48 h, an electron-lucid coarse granular component, possibly protein, was also secreted from the microvillar surface. By light microscopy, the mature 36-h membrane characteristically consisted of a dark anterior cap and posterior open ring, with a transparent intervening membrane and anterior plug. Ultrastructure of the fully formed membrane at 24-48 h was highly variable. Undifferentiated membranes appeared as a single electron-lucid layer; differentiated membranes were more complex, sometimes two-layered, containing electron-lucid and -dense fibers and granules. Results of binding to succinylated wheat germ agglutinin, histochemistry, and amino acid analysis indicated that the membrane was composed of chitin, glycoprotein, and protein. Eighteen amino acids were identified in membrane proteins; aspartic-glutamic acids (and amides), serine, glycine, and lysine (45% by weight) may be important in cross-linking membrane components.

Animals↗
PubMed1993

Dispersal of the sand fly Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Mark-release-recapture studies were carried out during 1990-1991 in El Callejón, Colombia, an endemic focus of American visceral leishmaniasis, to study the longevity, dispersal, and flight range of the principal vector, Lutzomyia longipalpis Lutz & Neiva. Several groups of wild-caught (n = 1,539) and laboratory-reared F1 (n = 2,208) sand flies were marked with fluorescent dusts and released. Recaptures at daytime resting sites, on animal bait, and in CDC light traps were made for 20 d following each release. From 2 to 9% of L. longipalpis were recaptured, a rate which differed between the sexes (7.7% male, 1.5% female). Overall, 49% of the L. longipalpis were recaptured between 0 and 50 m, 48% within 100 and 300 m, and nearly 3% at > or = 0.5 km from the release site. Sex differences in recapture site, distance flown, and direction were observed. Our results indicate that the dispersal behavior of peridomestic populations of L. longipalpis compares more closely with that of Old World sand fly species from similar habitats than to the sylvan Neotropical phlebotomines.

Animals↗
PubMed1993

Life cycle of Leishmania major (Kinetoplastida: Trypanosomatidae) in the neotropical sand fly Lutzomyia longipalpis (Diptera: Psychodidae).

The development of Leishmania major Yakimoff & Schokhor in the New World sand fly Lutzomyia longipalpis (Lutz & Neiva) was examined by light and electron microscopy. In this unnatural host, parasites differentiated into 10 typical morphological forms, multiplied at three sites, migrated anteriorly and established in the foregut, and attached to gut surfaces. In the blood meal, amastigotes divided and transformed into two successive dividing, stumpy promastigote stages. Elongate nectomonad promastigotes developed from stumpy forms and subsequently rounded up in some flies into paramastigotes and opisthomastigotes. Differentiation into round opisthomastigotes and the apparent fusion of paramastigotes in the blood meal were novel observations in this study. Three nectomonad promastigotes--elongate, short, and metacyclic--were free-swimming in the midgut lumen. Elongate nectomonad promastigotes were highly oriented in the midgut, with their flagella embedded between the epithelial microvilli. Short haptomonad promastigotes were the predominant form attached to the intima of the stomodeal valve, whereas pear-shaped haptomonad promastigotes and paramastigotes colonized surfaces of the esophagus and pharynx. Peripylarian attachment of promastigotes and paramastigotes in the pylorus, ileum, and colon was noted in 21% of flies, suggesting that suprapylarian leishmanias have not lost the ability to colonize the hindgut. L. longipalpis was a successful biological host for L. major, allowing complete development of the parasite.

Animals↗
PubMed1993

Genetic transformation and phylogeny of bacterial symbionts from tsetse.

Two isolates of bacterial endosymbionts, GP01 and GM02, were established in cell free medium from haemolymph of the tsetse, Glossina pallidipes and G. morsitans. These microorganisms appear similar to rickettsia-like organisms reported previously from various tsetse species. The 16S rRNA sequence analysis, however, placed them within the gamma subdivision of the Proteobacteria, phylogenetically distinct from most members of the Rickettsiaceae which align with the alpha subdivision. Distinct multiple endogenous plasmids are harboured by GP01 and GM02, suggesting that the two isolates are different. Restriction mapping analysis showed that one of the conserved plasmids is present in high copy number and is at least 80 kb in size. A heterologous plasmid pSUP204, which contains the broad host range oriV replication origin, was used to transfect bacterial cultures. The symbiont GM02 was transformed, and it expressed plasmid encoded resistance to the antibiotics ampicillin, tetracycline and chloramphenicol. Transformation of these symbionts may provide a novel means for expressing anti-parasitic genes within tsetse populations.

Animals↗
PubMed1993

Leishmaniases of the New World: current concepts and implications for future research.

Recent epidemiologic studies indicate that leishmaniasis in the Americas is far more abundant and of greater public health importance than was previously recognized. The disease in the New World is caused by a number of different parasite species that are capable of producing a wide variety of clinical manifestations. The outcome of leishmanial infection in humans is largely dependent on the immune responsiveness of the host and the virulence of the infecting parasite strain. This article reviews current concepts of the clinical forms, immunology, pathology, laboratory diagnosis, and treatment of the disease as well as aspects of its epidemiology and control. Recommendations for future research on the disease and its control are made.

Animals↗
PubMed1993

Field studies on the epidemiology of Venezuelan hemorrhagic fever: implication of the cotton rat Sigmodon alstoni as the probable rodent reservoir.

During February 1992, field studies on the epidemiology of Venezuelan hemorrhagic fever (VHF) were carried out in a rural area of Portuguesa State in central Venezuela. The objective of this work was to determine the prevalence of infection with Guanarito virus, the etiologic agent of VHF, among wild rodents and humans living within an endemic focus of the disease. A total of 234 rodents, representing nine different species, were collected and their spleens were cultured for virus. Thirty-one Guanarito virus isolates were made from two rodent species: 19 from 40 Sigmodon alstoni and 12 from 106 Zygodontomys brevicauda. Guanarito virus antibody rates among these two species were 5.1% and 15.0%, respectively. Nine of the 12 Z. brevicauda that yielded virus from their spleens also had Guanarito virus antibodies in their sera. In contrast, none of the 19 Guanarito virus-positive S. alstoni had antibodies to the virus. These data suggest that S. alstoni usually develops a persistent nonimmunizing infection with Guanarito virus, while Z. brevicauda develops an immunizing infection. Based on knowledge of the behavior of other human pathogenic arenaviruses, these results imply that S. alstoni is the principal rodent reservoir of Guanarito virus in nature. To determine the prevalence of Guanarito virus infection among humans in the same region, 195 people living near one of the rodent collecting sites were bled and their sera were tested for antibodies to the virus. Five individuals (2.6%) had Guanarito virus antibodies; all were adults, and two had been diagnosed previously as having VHF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Host preferences of the sand fly Lutzomyia longipalpis at an endemic focus of American visceral leishmaniasis in Colombia.

Blood meals from 579 Lutzomyia longipalpis (Diptera:Psychodidae), collected in an endemic focus of American visceral leishmaniasis in Colombia, were identified by precipitin test. Sand fly collections were made during a 16-month period from the inside walls of two houses, a pigpen, and rock crevices in a small community (El Callejon) within the endemic area. Feeding patterns of the sand flies varied with locality and date of collection. Overall, bovine feedings predominated, but feedings were also recorded on pigs, equines, humans, dogs, opossums, birds, and reptiles. Calculation of the forage ratios for each host species indicated that cows and pigs were the preferred hosts of Lu. longipalpis in El Callejon. Results of this study suggest that Lu. longipalpis is an opportunistic feeder and is not highly anthropophilic nor strongly attracted to dogs.

Animals↗
PubMed1992

Infectivity and pathogenesis of iridescent virus type 22 in various insect hosts.

This paper reports the results of a series of laboratory experiments to determine the infectivity and pathogenesis of iridescent virus type 22 (IV 22) for six species of mosquitoes, phlebotomine sand flies and triatomid bugs. Following inoculation, IV 22 replicated in all of the species tested, without producing noticeable mortality within a 14 day observation period. Examination of the infected insects by immunofluorescence demonstrated large amounts of viral antigen in many different organs. Electron microscopy done on infected mosquitoes (Aedes aegypti) showed large numbers of virus particles within cells of the fat body, muscle tracheal and midgut epithelium. Virus replication in the mosquitoes was confirmed to host cell cytoplasm and was similar to that described in the natural blackfly (Simulium) host. Transovarial transmission of IV 22 could not be demonstrated in A. aegypti, and only a small percentage of mosquito larvae could be infected orally. Results of these experiments are compatible with observations of other iridescent viruses; IV 22 is highly infectious for a wide range of insects when introduced into their hemolymph, but it is not very infectious per os. These characteristics would appear to limit its value as a potential biocontrol agent for Diptera.

Animals↗
PubMed1992

Isolation of bluetongue and epizootic hemorrhagic disease viruses from mosquitoes collected in Indonesia.

Three viruses isolated from anopheline mosquitoes in Indonesia have been identified as bluetongue and epizootic hemorrhagic disease viruses. Another virus isolate showed no relationship to other orbiviruses tested and should be regarded as a new virus; the name Golok is proposed for it. The mosquitoes were collected in 1980 and 1981 in a program designed to isolate flaviviruses infecting humans. It is apparent that such collections of arthropods which feed on large mammals could be screened for other viruses which may infect domestic livestock.

Animals↗
PubMed1992

Trans-beta-farnesene as a feeding stimulant for the sand fly Lutzomyia longipalpis (Diptera: Psychodidae).

The aphid alarm pheromone, trans-beta-farnesene (TBF), was found to stimulate feeding in both male and female Lutzomyia longipalpis Lutz & Neiva. Four other structurally related compounds (farnesol; 808 farnesene; trans, trans-farnesyl acetate; farnesyl methyl ether) were slightly less stimulating to these insects. The effect of TBF varied with sand fly age and the concentration of the chemical used. In contrast, TBF did not stimulate feeding in either sex of four other sand fly species (L. shannoni Dyar, Phlebotomus papatasi (Scopoli), P. argentipes Annandale & Brunetti, P. perniciosus Newstead). TBF might be useful in enhancing L. longipalpis field collections or in developing a poison bait for the control of this species.

Animals↗