Biomedical subjects

R B Tesh

Publications and source records attributed to R B Tesh.

At least 73 records · Page 4Linked to original sources

PubMed1992

Transformation of an insect symbiont and expression of a foreign gene in the Chagas' disease vector Rhodnius prolixus.

A shuttle plasmid was developed that is capable of replicating both in Escherichia coli and in Rhodococcus rhodnii, a bacterial symbiont of the Chagas' disease vector Rhodnius prolixus. We have been able to transform R. rhodnii with this plasmid, infect aposymbiotic R. prolixus with the transformed symbionts, select with the antibiotic thiostrepton, and re-isolate genetically altered symbionts from the insects following successive molts. Symbiotic bacteria are potentially valuable as vehicles for the stable introduction of foreign genes into insects with the goal of eventually altering the ability of the insect to transmit a pathogenic agent.

Animals↗

PubMed1992

Ultrastructural aspects of replication of the New Jersey serotype of vesicular stomatitis virus in a suspected sand fly vector, Lutzomyia shannoni (Diptera: Psychodidae).

Transmission electron microscopy was used to examine replication of the New Jersey serotype of vesicular stomatitis virus (VSNJ) (Rhabdoviridae: Vesiculovirus) in Lutzomyia shannoni (Diptera: Psychodidae), a recently implicated sand fly vector. Following ingestion of an infectious blood meal, female sand flies were fixed and examined at approximately 12-hr intervals for six days. The New Jersey serotype of vesicular stomatitis virus was first detected in the abdominal midgut after 34 hr of incubation. Virus next appeared in fat body and the thoracic midgut at 48 hr, while salivary glands first contained visible virus in apical cavities 5-6 days after infection. Flight muscles and nervous tissue occasionally contained small numbers of VSNJ virions, while virus was never detected in the ovaries or malphigian tubules. The midgut and fat body appeared to be major sites of VSNJ virus replication. In all tissues examined, virus matured primarily by budding from the plasma membrane. Virions were occasionally observed within vacuoles, along with nucleocapsids. In the midgut, budding occurred exclusively from the basolateral plasma membrane, while maturation in salivary gland cells involved apical budding. Accumulation of virions adjacent to basal laminae surrounding several tissues suggested that this structure physically impedes virus dissemination within the sandfly. The paucity of virus budding 120-144 hr after infection suggested that the VSNJ virus infection was modulated in Lu. shannoni.

Animals↗

PubMed1992

Refractory barriers in the sand fly Phlebotomus papatasi (Diptera: Psychodidae) to infection with Leishmania panamensis.

The life cycle of Leishmania panamensis in Phlebotomus papatasi was studied to characterize barriers limiting parasite colonization, differentiation, migration, and attachment in an unnatural sand fly host. The insects were fed a suspension of L. panamensis-infected macrophages and human erythrocytes, and were examined up to 16 days post-infection by light and electron microscopy. Histologic examination of 401 flies showed the peritrophic membrane to be the first important barrier to parasite establishment in the gut lumen. In most flies, parasites were unable to escape from the closed peritrophic sac, which was either excreted or retained intact in the midgut. After five days, only 31% of the flies were infected; attached parasites colonized the pylorus-ileum and/or colon regions of the hindgut. Anterior migration into the cardia region of the midgut occurred in less than 1% of infected flies; no parasites colonized the foregut. In the bloodmeal and residual bloodmeal, five morphologic forms developed from ingested amastigotes: stumpy, spatulate, elongate, short nectomonad promastigotes, and paramastigotes. Abnormal retention of amastigotes in macrophages and delayed development of promastigote stages was observed. The primary form attached in the hindgut was a pear-shaped haptomonad promastigote. Differentiation of L. panamensis in Ph. papatasi appeared to be similar to that described in natural hosts, except that metacyclic infective forms were not observed, and some forms developed in unusual locations. Phlebotomus papatasi was a partly refractory biological host for L. panamensis. The peritrophic membrane adversely affected the infection rate; rare anterior migration and a lack of metacyclic promastigotes may preclude transmission by bite.

Animals↗

PubMed1992

Simulation of arbovirus overwintering: survival of Toscana virus (Bunyaviridae:Phlebovirus) in its natural sand fly vector Phlebotomus perniciosus.

A series of experiments were done to study the effect of simulated summer and winter temperatures on the development of Phlebotomus perniciosus (Diptera:Psychodidae) and on the survival of Toscana virus in transovarially infected insects. Sand flies maintained at 28 degrees C developed relatively fast, with adults emerging from 40 to 55 days after initial oviposition. Similar results were obtained with insects reared at 25 degrees C. In contrast, sand flies maintained at 15 degrees C developed slowly up to the fourth larval instar; at that point, further development ceased and the insects entered diapause. Diapause could be terminated by increasing the ambient temperature to 25 degrees C. The ambient temperatures at which the immature forms were reared (15 degrees C, 25 degrees C, and 28 degrees C) had no effect on the subsequent F1 adult filial infection rates with Toscana virus (49.1%, 47.5%, and 46.5%, respectively). The results of these experiments provide a model of how Toscana virus survives the winter in endemic areas by maintenance in diapausing P. perniciosus larvae. In another experiment, venereal transmission of Toscana virus was shown from transovarially infected males to non-infected virgin females. This is the first demonstration of sexual transmission of a phlebovirus by sand flies. If venereal transmission occurs in nature, it would provide an alternative method of virus amplification in the vector population, in the absence of viremic vertebrates.

Animals↗

PubMed1992

A new genotype of Japanese encephalitis virus from Indonesia.

Primer-extension sequencing of the RNA template of polio, dengue, Rift Valley fever, and Japanese encephalitis (JE) viruses has provided new information on their geographic distribution, origin, and evolution. In a previous study of 46 diverse JE virus strains, we demonstrated the existence of three distinct JE genotypes in Asia. We now report the occurrence of a fourth genotype. In the present study, 19 JE virus isolates, representing various geographic regions of Asia and a 50-year time span, were compared with each other and with Murray Valley encephalitis, West Nile, and Kunjin viruses. Twelve of the JE strains from the Indonesian Archipelago and the Philippines had not been previously examined; the remainder were representatives of the three previously identified genotypes. Two hundred forty nucleotides from the pre-M gene region of the virus were used in these comparisons. Using 12% divergence as a cut-off point, the 19 JE strains fell into four distinct genotypic groups; maximum divergence across the comparison region was 21%. The newly recognized fourth genotype was comprised of five Indonesian isolates that were 7% divergent from the rest of the JE viruses.

Amino Acid Sequence↗

PubMed1991

Venezuelan haemorrhagic fever.

An outbreak of severe haemorrhagic illness began in the municipality of Guanarito, Portuguesa State, Venezuela, in September, 1989. Subsequent detailed study of 15 cases confirmed the presence of a new viral disease, designated Venezuelan haemorrhagic fever. Characteristic features are fever, toxicity, headache, arthralgia, diarrhoea, conjunctivitis, pharyngitis, leucopenia, thrombocytopenia, and haemorrhagic manifestations. Other features include facial oedema, cervical lymphadenopathy, nausea/vomiting, cough, chest or abdominal pain, and convulsions. The patients ranged in age from 6 to 54 years; all were residents of rural areas in central Venezuela, and 9 died. Infection with Guanarito virus, a newly recognised arenavirus, was shown by direct culture or by serological confirmation in all cases. Epidemiological studies suggest that the disease is endemic in some rural areas of central Venezuela and that it is rodent-borne. Venezuelan haemorrhagic fever has many similarities to Lassa fever and to the arenavirus haemorrhagic fevers that occur in Argentina and Bolivia.

Acute Disease↗

PubMed1991

Effect of ivermectin on the ovarian development of Aedes aegypti (Diptera: Culicidae).

The effect of ivermectin (0.1 microgram/ml) on blood digestion, ovarian development, and ovipositional attributes of Aedes aegypti was studied using standard morphological and histological techniques. Uncoordinated movements and paralysis were observed in most ivermectin-treated females within 1 h after ingestion of blood containing the chemical. Eight days after the blood meal, 23.5% of the treated females had died, whereas no mortality occurred in controls. Formation of the peritrophic membrane and digestion of the blood meal were delayed in the surviving treated mosquitoes. The most striking effect of ivermectin on Ae. aegypti at this dosage was on ovarian development. Changes observed among ivermectin-treated mosquitoes included: blood digestion without development of ovarian follicles; degeneration of primary follicles and formation of ovarian dilatations within 24 h after ingestion of the chemical; significant reduction in the rate of vitellogenesis and follicle development; decreased egg production; reduced egg hatching; abnormal egg size and shape; and increased percentages of unhatched embryonated and sterile eggs. Although the precise action of ivermectin on Ae. aegypti is unknown, our studies indicate that the chemical directly or indirectly affects at least three major organ systems (nervous, digestive, and reproductive).

Aedes↗

PubMed1991

Characterization of Leishmania colombiensis sp. n (Kinetoplastida: Trypanosomatidae), a new parasite infecting humans, animals, and phlebotomine sand flies in Colombia and Panama.

Characterization of Leishmania colombiensis sp.n. is presented, which on the basis of biological and molecular criteria, appears to be a new member of the L. braziliensis complex. A total of nine isolates of the new parasite were made in Colombia and Panama between 1980 and 1986: two from human cases of cutaneous leishmaniasis, six from phlebotomine sand flies, and one from a sloth. Although most closely related to L. lainsoni, L. colombiensis sp.n. is clearly distinguishable from other members of the genus by its reactivity with monoclonal antibodies, isoenzyme electrophoresis, and restriction endonuclease fragment patterns of kinetoplast DNA (k-DNA).

Adult↗

PubMed1991

Phlebotomine sand flies as vectors of vesiculoviruses: a review.

Phlebotomine sand flies appear to be involved in the epizootiology of 10 of the 16 currently recognized vesiculoviruses. Evidence in support of this includes isolation of viruses from wild-caught male and female sand flies; demonstration of oral infection, replication, and bite transmission of viruses by sand flies; the temporal and/or spatial association between infected sand flies and infected vertebrates; and demonstration of transovarial virus transmission. The present review summarizes the known sand fly-vesiculovirus relationships.

Animals↗

PubMed1990

Size-conserved chromosomes and stability of molecular karyotype in cloned stocks of Leishmania major.

Molecular karyotypes for 5 stocks of Leishmania major were derived by pulsed-field gradient gel electrophoresis and transverse alternating field electrophoresis. Chromosome sizes obtained by the two methods agreed within less than or equal to 50kb. A set of 10 size-concordant chromosome bands between approx. 350-1000 kb was found in all stocks, plus a variable number of polymorphic chromosomes. Cloned gene probes, and DNA purified from individual chromosomes, hybridized to individual size-concordant chromosomes in different stocks, indicating a high degree of sequence homology among bands of similar size. Since the stocks were isolated over a 25-year period in a wide geographic area, we interpret these size-conserved chromosomes to be characteristic of the L. major karyotype. We were unable to identify irreversible genomic rearrangements in Leishmania cloned from the midgut of sandflies or cultivated from the skins of infected mice, which might have explained the origin of the size-variable chromosomes. For stocks that are maintained in the laboratory, the molecular karyotype appears to be a stable characteristic of a cloned population of Leishmania.

Animals↗

PubMed1990

Genetic variation of Japanese encephalitis virus in nature.

Forty-six strains of Japanese encephalitis (JE) virus from a variety of geographic areas in Asia were examined by primer-extension sequencing of the RNA template. A 240 nucleotide sequence from the pre-M gene region was selected for study because it provided sufficient information for determining genetic relationships among the virus isolates. Using 12% divergence as a cutoff point for virus relationships, the 46 isolates fell into three distinct genotypic groups. One genotypic group consisted of JE virus isolates from northern Thailand and Cambodia. A second group was composed of isolates from southern Thailand, Malaysia, Sarawak and Indonesia. The remainder of the isolates, from Japan, China, Taiwan, the Philippines, Sri Lanka, India and Nepal, made up a third group. The implications of these findings in relation to the epidemiology of JE are discussed. Results of this study demonstrate that the comparison of short nucleotide sequences can provide insight into JE virus evolution, transmission and, possibly, pathogenesis.

Animals↗

PubMed1990

Distribution and etiology of leishmaniasis in Colombia.

A total of 340 Leishmania strains, isolated from humans, animals, and sand flies from various regions of Colombia, were examined by isozyme electrophoresis. Seven different Leishmania species were identified. Leishmania panamensis and L. braziliensis were the most common, representing 53.8% and 30.3% of the total, respectively. Isolation rates of the other species were as follows: L. chagasi, 9.4%; L. guyanensis, 2.6%; L. amazonensis, 1.8%; L. mexicana, 0.8%; and a new species requiring additional study, 1.2%. Statistical analyses of representative L. panamensis and L. braziliensis isolates indicated that the populations of these 2 species are genetically very similar. L. panamensis may have a continuous distribution in Colombia west of the eastern Andes Mountains and L. braziliensis may have a continuous distribution east of the western Andes Mountains. Information is given on disease manifestations of the parasites in human hosts and on isolation records from sand flies and animals.

Animals↗

PubMed1990

Selection of Phlebotomus papatasi (Diptera: Psychodidae) lines susceptible and refractory to Leishmania major infection.

Variation in susceptibility to infection with cultured promastigotes of Leishmania major was detected among 3 different geographic strains (ISRAEL, EGYPT, and INDIA) of the sand fly Phlebotomus papatasi. The ISRAEL strain showed the greatest susceptibility and was chosen for subsequent genetic selection experiments. After 13 generations of genetic selection in this strain, a stable refractory line was obtained in which only 7.5% of the insects could be infected. A highly susceptible line was also obtained in 5 generations of selection. Infection rates in the susceptible line were stabilized at about 94%. A description of the selection process and characteristics of the 2 lines are given.

Animals↗

PubMed1990

Genetic factors controlling susceptibility to Leishmania major infection in the sand fly Phlebotomus papatasi (Diptera: Psychodidae).

Studies of the genetic factors controlling Leishmania major infection in Phlebotomus papatasi were carried out using 2 different sand fly lines: one highly susceptible and the other refractory to the parasite. L. major infection rates in both F1 and F2 generations from reciprocal crosses and in backcrosses between the parent lines showed that susceptibility and refractoriness of Ph. papatasi to infection with L. major are controlled by less than 1 gene. Neither susceptibility nor refractoriness is dominant over the other.

Animals↗

PubMed1990

Vesicular stomatitis virus, New Jersey serotype: replication in and transmission by Lutzomyia shannoni (Diptera: Psychodidae).

Laboratory-reared female sand flies (Lutzomyia shannoni) were experimentally infected, orally and by intrathoracic inoculation, with the New Jersey serotype of vesicular stomatitis (VSNJ) virus. Virus replication occurred in the insects following infection by both routes. Virus titers greater than 10(4) plaque forming units of VSNJ virus were present in heads of orally infected sand flies 12 days after virus ingestion, confirming that a persistent disseminated infection had occurred. Both orally and parenterally infected Lu. shannoni transmitted VSNJ virus by bite to susceptible rodents and by transovarial transmission to a small percentage of their F1 progeny. The significance of these findings in the epizootiology of VSNJ virus on Ossabaw Island, Georgia, an enzootic focus of this virus, is discussed.

Animals↗

PubMed1990

Mortality and infertility in adult mosquitoes after the ingestion of blood containing ivermectin.

Mosquitoes of 3 species (Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus) were fed on human blood containing various concentrations of ivermectin. Three effects (death, decreased egg production, and reduced egg hatching) were observed in the insects, depending upon the concentration of ivermectin ingested. The LD50 of ivermectin in human blood for the 3 mosquito species was estimated to be 126, 208, and 698 ng/ml, respectively. Mosquitoes dying after ingestion of ivermectin developed signs of acute toxicity including paralysis, lethargy, incoordination, and difficulty in movement. Death usually occurred within 48-72 hr. With sublethal blood concentrations of the chemical, mosquitoes survived, but there was a marked reduction in both the number and viability of their eggs. This infertility was only temporary, however, as subsequent refeeding of the insects on uncontaminated blood resulted in the production of normal numbers of fertile eggs. Blood levels of ivermectin which made 50% of the eggs infertile in Ae. aegypti and Ae. albopictus were calculated 3.4 and 4.3 ng/ml, respectively. These latter concentrations of the chemical are within the range found in blood of humans and domestic animals receiving ivermectin for treatment of parasitic infections. This finding suggests that the widespread use of ivermectin in veterinary and human medicine may have an unrecognized effect on mosquito populations.

Aedes↗

PubMed1989

A novel vasodilatory peptide from the salivary glands of the sand fly Lutzomyia longipalpis.

Salivary gland lysates of the sand fly Lutzomyia longipalpis contain a potent vasodilator that aids the fly to feed on the blood of its vertebrate hosts. Chromatographic analysis, antibody reactivity, and data obtained from bioassays of the salivary erythema-inducing factor indicate striking similarity with human calcitonin gene-related peptide. The erythema-inducing factor is, however, at least one order of magnitude more potent than calcitonin gene-related peptide.

Animals↗

PubMed1989

Bivens arm virus: a new rhabdovirus isolated from Culicoides insignis in Florida and related to Tibrogargan virus of Australia.

During field studies in 1981 on the transmission of bluetongue viruses in ruminants in Florida, a virus was isolated from Culicoides insignis collected near water buffalo (Bubalus bubalis) recently imported from Trinidad. Electron microscopy showed that this isolate, for which the name Bivens Arm virus is proposed, has rhabdovirus morphology. Serologic comparisons were made with recognized rhabdoviruses from terrestrial vertebrates and hematophagous arthropods. Indirect fluorescent antibody, complement fixation and neutralization tests indicated antigenic reactivity between Bivens Arm virus and two rhabdoviruses found only in Australia, Tibrogargan and Coastal Plains viruses. The Australian isolates cause subclinical infections in cattle and water buffalo and are believed to be transmitted by Culicoides. Initially, it was thought that Bivens Arm virus may have been introduced to Florida with the water buffalo from Trinidad, but a serologic survey of cattle serum, collected before the importation of the buffalo revealed antibody to the virus in cattle on farms located in diverse areas of Florida.

Animals↗