PubMed Health⌕ Search

Biomedical subjects

R B Tesh

Publications and source records attributed to R B Tesh.

At least 37 records · Page 2Linked to original sources
PubMed1999

Isolation and genetic characterization of a hantavirus (Bunyaviridae: Hantavirus) from a rodent, Oligoryzomys microtis (Muridae), collected in northeastern Peru.

This paper describes the isolation and partial genetic characterization of a hantavirus from a pygmy rice rat, Oligoryzomys microtis, collected within the urban area of Iquitos, Loreto Department, Peru. The virus, designated HTN-007, exhibited the highest degree of genetic similarity to Rio Mamore virus, which was originally described from the same rodent species in eastern Bolivia. Comparison of small and medium segment nucleotide sequence data from HTN-007 and Rio Mamore virus revealed 87% and 85% sequence identity, respectively. Based on these analyses, HTN-007 appears to be a variant of Rio Mamore virus. As such, it represents the first successful isolation of Rio Mamore virus and the first evidence for the existence of a hantavirus in Peru. Serologic studies done by immunofluorescence on blood samples of 56 O. microtis trapped at the collection site indicated that 21.4% had antibodies to hantavirus. In view of the proximity of this rodent species to humans and the close phylogenetic relationship of Rio Mamore virus to hantaviruses that have been associated with human disease, Rio Mamore virus may be a hantavirus of some public health importance in tropical South America.

Animals↗
PubMed1998

Venezuelan hemorrhagic fever: clinical and epidemiological studies of 165 cases.

Epidemiological and clinical data are presented on 165 cases of Venezuelan hemorrhagic fever (VHF), a newly emerging viral zoonosis caused by Guanarito virus (of the family Arenaviridae). The disease is endemic in a relatively circumscribed area of central Venezuela. Since its first recognition in 1989, the incidence of VHF has peaked each year between November and January, during the period of major agricultural activity in the region of endemicity. The majority of cases have involved male agricultural workers. Principal symptoms among the patients with VHF included fever, malaise, headache, arthralgia, sore throat, vomiting, abdominal pain, diarrhea, convulsions, and a variety of hemorrhagic manifestations. The majority of patients also had leukopenia and thrombocytopenia. The overall fatality rate among the 165 cases was 33.3%, despite hospitalization and vigorous supportive care.

Hemorrhagic Fevers, Viral↗
PubMed1998

Ultrastructural differentiation of the genogroups in the genus Ehrlichia.

Ultrastructural characteristics of 15 strains and isolates of ehrlichiae belonging to three genogroups, or clades of genetically related organisms united in the genera Ehrlichia, Cowdria, Anaplasma, Neorickettsia and a strain of Wolbachia pipientis which represents a fourth genogroup in this cluster of species, were studied in continuous cell culture or in vivo: E. canis (Oklahoma strain and VHE isolate), E. muris (AS 145), E. chaffeensis (Arkansas, 91HE17 and Sapulpa), human granulocytic ehrlichiae (HGE)(BDS, 96HE27, 96HE37, #54, #55 and #72), E. equi (MRK), E. sennetsu (Miyayama), E. risticii (HRC-IL). Wolbachia pipientis was studied in the naturally infected Aedes albopictus mosquito cell line Aa23. All organisms were similar in the normal ultrastructure of individual cells and in the ability to form abnormal, pathological ehrlichial cells of the same type irrespective of the species. Normally all ehrlichiae studied in cell culture existed in two morphological forms - reticulate and dense-cored cells, both of which could divide by binary fission. Most alterations were related to their membranes, especially the cell wall. Differences in the structure of intravacuolar microcolonies (morulae) of ehrlichiae and their inter-relations with the host cells allowed differentiation of the genogroups: the E. canis-E. chaffeensis-E. muris genogroup formed large morulae, with many ehrlichiae, often suspended in a fibrillar matrix, and the host cell mitochondria and endoplasmic reticulum usually aggregated near the morulae and were in contact with the morula membrane; the E. phagocytophila-E. equi-HGE group morulae had no fibrillar matrix, no contacts with host cell mitochodria, and they did not aggregate around the morulae; E. sennetsu-E. risticii group usually developed in small individual vacuoles that did not fuse with each other and divided along with the ehrlichiae.

Animals↗
PubMed1997

Isolation, characterization and geographic distribution of Caño Delgadito virus, a newly discovered South American hantavirus (family Bunyaviridae).

Rodents collected from the Venezuelan llanos (plains) during field studies of viral hemorrhagic fever were tested for evidence of hantavirus infection. Hantavirus antibody was found in one (7.7%) of 13 Oryzomys bicolor, one (3.4%) of 29 Rattus rattus, 10 (6.0%) of 166 Sigmodon alstoni and one (2.2%) of 45 Zygodontomys brevicauda. Hantavirus-specific RNA was detected in lung tissues from four antibody-positive rodents: two S. alstoni from Portuguesa State and one S. alstoni each from Cojedes and Barinas States. A hantavirus isolate (herein identified as VHV-574) was recovered from lung tissue from a hantavirus RNA-positive S. alstoni collected from Portuguesa State. The results of serological tests and analyses of small and medium RNA segment nucleotide sequence data indicated that VHV-574 represents a novel hantavirus (proposed name 'Caño Delgadito') that is distinct from all previously characterized hantaviruses. The results of analyses of nucleotide sequence data from the four hantavirus RNA-positive S. alstoni suggested that Caño Delgadito virus is widely distributed in the Venezuelan llanos.

Animals↗
PubMed1997

In vitro cultivation of Wolbachia pipientis in an Aedes albopictus cell line.

A continuous cell line, Aa23, was established from eggs of a strain of the Asian tiger mosquito, Aedes albopictus, naturally infected with the intracellular symbiont Wolbachia pipientis. The resulting cell line was shown to be persistently infected with the bacterial endosymbiont. Treatment with antibiotics cured the cells of the infection. In the course of establishing this cell line it was noticed that RFLPs in the PCR products of two Wolbachia genes from the parental mosquitoes were fixed in the infected cell line. This indicates that the mosquito host was naturally superinfected with different Wolbachia strains, whereas the infected cell line derived from these mosquitoes only contained one of the original Wolbachia strains. The development of an in vitro culture system for this fastidious microorganism should facilitate molecular analysis of the reproduction distorting phenotypes it induces in natural arthropod hosts.

Aedes↗
PubMed1997

Development of Endotrypanum (Kinetoplastida:Trypanosomatidae) in experimentally infected phlebotomine sand flies (Diptera:Psychodidae).

The developmental biology (parasite establishment, migration, and differentiation) of Brazilian strains of Endotrypanum are reported for 3 sand fly species: Lutzomyia longipalpis Lutz & Neiva, L. shannoni Dyar, and Phlebotomus papatasi Scopoli. Laboratory-reared sand flies were infected by feeding on a promastigote suspension through a chick-skin membrane. Infections within the insect gut were examined at various times after feeding by staining fresh and fixed specimens. Development of Endotrypanum varied for each parasite-host species association. After feeding on culture forms of E. schaudinni Mesnil & Brimont (strain ISHA/BR/80/IM1111), significantly more L. shannoni (100%, 9/9) became infected than did L. longipalpis (62.3%, 33/53) or P. papatasi (27.3%, 15/55). The greatest number of infections were in the midgut and hindgut from 6 to 16 d after feeding, but flagellates also were present in the Malpighian tubules. Moreover, distinct development patterns in the sand fly gut were obtained when the Callejon L. longipalpis colony was fed on cultures of other Endotrypanum strains. Significantly fewer sand flies became infected with strain MCHO/BR/85/IM2259 (18.2%, 4/22) than with strain ISHA/BR/80/IM1111 (55.6%, 20/36). There were also individual variation in the distribution and survival of parasites within the guts of flies in each group. These data indicate that there is variation in the susceptibility to infection with Endotrypanum among and within sand fly species.

Animals↗
PubMed1997

Isolation and characterization of pirital virus, a newly discovered South American arenavirus.

Specific rodent species are principal hosts for each of the well-characterized members of the virus family Arenaviridae. Guanarito virus (Arenaviridae) is the etiologic agent of Venezuelan hemorrhagic fever. A previous study on the epidemiology of Venezuelan hemorrhagic fever revealed extensive arenavirus infection (presumed to be caused by Guanarito virus) in two rodent species. Sigmodon alstoni and Zygodontomys brevicauda, collected from the region of Venezuela in which the disease is endemic. In the present study, four arenavirus isolates recovered from the Municipality of Guanarito (two isolates each from S. alstoni and Z. brevicauda) were characterized to learn more about the natural rodent host relationships of Guanarito virus. Serologic tests and analyses of nucleocapsid protein gene sequence data indicated that the two isolates from Z. brevicauda are strains of Guanarito virus and that the two isolates from S. alstoni are representatives of a novel New World arenavirus (proposed name Pirital) that is antigenically and phylogenetically distinct from all known New World arenaviruses. The results of the present study provide further evidence that the cane mouse Z. brevicauda is a natural host of Guanarito virus and suggest that the cotton rat S. alstoni is the natural reservoir host of Pirital but not Guanarito virus.

Animals↗
PubMed1996

Genetic variation in yellow fever virus: duplication in the 3' noncoding region of strains from Africa.

The nucleotide sequences of three regions of the genomes of 13 yellow fever (YF) virus isolates were determined to define genetic variation and evolution of the virus. Phylogenetic trees generated from sequences of either the 5' terminal 1320 nucleotides of the genome, 754 nucleotides from the NS4A and NS4B genes, or the 3' terminal 511 nucleotides were very similar and contained minor differences. Overall, these results suggested that there were at least four major genotypes of YF virus, including one in Central/East Africa, one in West Africa, and two in South America. Examination of the 3' noncoding region (3'NCR) showed that only West African strains had a 3'NCR of 511 nucleotides while strains from Central/East Africa and South America had shorter 3'NCRs (443-469 nucleotides) due to the absence of YF specific repeat sequences (RYFs). Central/East African strains have two RYFs and West African strains have three RYFs while South American strains only have one copy of the RYF. It is speculated that duplication of the RYF took place in West Africa subsequent to the presumed introduction of YF virus into South America. Thus, both tick-borne (Mandl et al., J. Virol. 65, 4070-4077, 1991 and Wallner et al., Virology 213, 169-178, 1995) and mosquito-borne flaviviruses have variable 3'NCRs.

Africa↗
PubMed1996

Re-emergence of epidemic Venezuelan equine encephalomyelitis in South America. VEE Study Group.

BACKGROUND: Venezuelan equine encephalomyelitis (VEE) virus has caused periodic epidemics among human beings and equines in Latin America from the 1920s to the early 1970s. The first major outbreak since 1973 occurred in Venezuela and Colombia during 1995, and involved an estimated 75,000 to 100,000 people. We report an epidemiological and virological investigation of this epidemic. METHODS: Virus isolates were made in cell culture from human serum, human throat swabs, and brain tissue from aborted and stillborn human fetuses, as well as from horse brain tissue and pooled mosquito collections. Human sera were also tested for VEE-specific antibodies. The serotypes of VEE isolates were identified by antigen assays, and viruses were characterised genetically by sequencing PCR products generated from the E3 and E2 genes. Phylogenetic analyses were done to determine evolutionary relations with respect to previous epidemic/epizootic and enzootic VEE virus isolates. Mosquito collections were made to identify possible vectors, and clinical findings were determined by direct observation of patients visiting hospitals and clinics in affected regions, and by inspecting patient records. Equine vaccination and vector control were used in an attempt to halt the spread of the outbreak. FINDINGS: Most affected people had an acute, self-limited febrile illness of 3 to 4 days duration. However, convulsions were often seen in children, and abortions and fetal deaths occurred in pregnant women infected with VEE virus. Antigenic characterisation of 12 virus isolates spanning the temporal and spatial range of the outbreak indicated that all are VEE serotype IC. Phylogenetic analysis revealed that all of the 1995 viruses were closely related to serotype IC viruses isolated during a large VEE outbreak that occurred in the same regions of Colombia and Venezuela from 1962-1964. A 1983 mosquito isolate from north central Venezuela was also closely related to the 1995 isolates. INTERPRETATION: This outbreak was remarkably similar to one that occurred in same regions of Venezuela and Colombia during 1962-1964. Symptoms of infected patients, estimated mortality rates, meteorological conditions preceding the epidemic, and seasonal patterns of transmission were all very similar to those reported in the previous outbreak. In addition, viruses isolated during 1995 were antigenically and genetically nearly identifical to those obtained during 1962-1964. These findings suggest that the epidemic resulted from the re-emergence of an epizootic serotype IC VEE virus. Identification of a similar virus isolate in mosquitoes in Venezuela in 1983, 10 years after epidemic/epizootic VEE activity ceased, raises the possibility of a serotype IC enzootic transmission cycle in northern Venezuela.

Adolescent↗
PubMed1996

Characterization of Oliveros virus, a new member of the Tacaribe complex (Arenaviridae: Arenavirus).

Oliveros virus is an agent isolated in cell culture from Bolomys obscurus (Rodentia, Muridae, Sigmodontinae) captured on the central Argentine pampa. Oliveros virus was shown to be related to members of the Tacaribe complex of the family Arenaviridae by immunofluorescent antibody (IFA) tests, electrophoretic pattern of viral proteins, and morphology as observed by electron microscopy. It was distinct from 12 other arenaviruses by a combination of plaque-reduction neutralization tests, comparison of endpoint titers among cross-IFA tests, and comparison of viral RNA sequence data. This agent is the third new arenavirus from South America described within the last three years.

Animals↗
PubMed1995

Leishmania amazonensis: sensitivity of different promastigote morphotypes to salivary gland homogenates of the sand fly Lutzomyia longipalpis.

We have recently demonstrated that Lutzomyia longipalpis salivary gland homogenates (SGH) inhibited the multiplication of Leishmania promastigotes in vitro. The present work shows that Leishmania amazonensis sensitivity to SGH is correlated to the phase of promastigote in vitro growth and can be decreased by the addition of hemin to the culture medium. The possible relevance of these in vitro results is discussed in relation to the development of Leishmania parasites within their sand fly vectors.

Animals↗
PubMed1995

Species composition and relative abundance of sand flies of the genus Lutzomyia (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 at a small rural community in Colombia where American visceral leishmaniasis is endemic. Weekly sand fly collections were made from pigpens, houses, and natural resting sites, using hand-held aspirators, sticky (oiled) paper traps, and opossum-baited Disney traps. In total, 263,094 sand flies were collected; L. longipalpis predominated (86.1%), followed by L. trinidadensis (11.0%), L. cayennensis (2.7%), and 8 other Lutzomyia species. The species composition and sex ratio of these sand flies varied among sites and by collection method. L. longipalpis were captured most efficiently by direct aspiration from animal bait. Conversely, sticky paper traps, especially inside houses and at rock resting sites, collected a greater diversity of species, but a lower relative abundance of L. longipalpis.

Animals↗
PubMed1995

Seasonal abundance of Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1993 in a small rural community in Colombia where American visceral leishmaniasis is endemic. Standardized weekly sand fly collections made from pigpens and natural resting sites displayed a bimodal annual abundance cycle, with a small peak occurring in October-November and a larger one in April-May. Time series analysis was employed to quantify the associations between sand fly abundance and weather factors (temperature, relative humidity, and rainfall). In addition to a prominent 6-mo cycle. Fourier analysis of the collection data demonstrated that the L. longipalpis population also exhibited a 5- to 8-wk cycle that may represent the length of larval development. Autoregressive moving average models were fit to weekly collection data and their residuals were regressed against rainfall, temperature, and relative humidity. A significant positive association between female L. longipalpis abundance and the relative humidity and rainfall recorded 3 wk earlier was found, indicating that these factors may be of value in predicting sand fly abundance. Additionally, these data indicated that L. longipalpis larvae may become quiescent during adverse conditions.

Animals↗
PubMed1995

Nocturnal activity patterns of Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Nocturnal activity of the sand fly Lutzomyia longipalpis (Lutz & Neiva) was studied from August 1991 to July 1992 in a small rural community in Colombia where American visceral leishmaniasis is endemic. During 2 or 3 nights each month, sand flies were collected with hand-held aspirators each hour between 1730 and 0630 hours, from a pigpen and a cattle corral located 30 m apart. Host-seeking activity of L. longipalpis adults was characterized by 2 general patterns: (1) adult sand fly activity increased shortly after sunset and continued until just after sunrise, and (2) peak sand fly activity was greatest early in the evening (1830-2330 hours) and then declined steadily toward morning. Female L. longipalpis activity generally increased after 2030 hours, whereas that of males remained constant or declined as the evening progressed. There were seasonal differences in sand fly abundance between the 2 sites: peak abundance in the cattle corral occurred during hot, dry periods, whereas maximum abundance in the pigpen occurred when relative humidity was higher. Influence of relative humidity on activity varied with season. Sand fly activity tended to decrease at temperatures below 24 degrees C and increase in the presence of moonlight.

Animals↗
PubMed1995

Age structure, blood-feeding behavior, and Leishmania chagasi infection in Lutzomyia longipalpis (Diptera: Psychodidae) at an endemic focus of visceral leishmaniasis in Colombia.

Ecological studies on the sand fly Lutzomyia longipalpis (Lutz & Neiva) were conducted during 1990-1992 in a small rural community in Colombia where American visceral leishmaniasis (AVL) is endemic. Subsamples of sand flies collected weekly from pigpens, the interior of houses, and natural outdoor resting sites were dissected to determine physiological age and Leishmania chagasi Cunha & Chagas infection rates. Eleven female L. longipalpis had flagellates in their gut, 2 of which were successfully cultured and identified as Leishmania chagasi. The reproductive status, stage of ovarian development, and trophic history of female sand flies varied among sites, habitats, and time of collection. The percentage of parous females ranged from about one-third to two-thirds overall and varied seasonally. Of most relevance to AVL transmission was the finding that 8% of L. longipalpis females were multiparous. In addition, our data suggest that L. longipalpis rest inside houses after blood-feeding outdoors, and that this species can blood-feed more than once during a single gonotrophic cycle.

Aging↗
PubMed1995

Peritrophic envelopes of Lutzomyia spinicrassa (Diptera: Psychodidae).

The secretion, morphology, and chemical composition of the peritrophic envelope were studied in the phlebotomine sand fly, Lutzomyia spinicrassa Morales, OsornoMesa, Osorno & Hoyos, a suspected vector of Leishmania braziliensis in Colombia and Venezuela. Viewed under light microscopy, the envelope matured rapidly and could be dissected from the blood bolus as early as 12 h and until 36 h after feeding; subsequently it began to degrade. The envelope was initially a closed sac around the blood meal, but opened posteriorly in most flies by 6 h. The posterior opening may facilitate the migration and establishment of Le. braziliensis in the hindgut. Secretion of envelope precursors was from the entire midgut epithelium. Electron microscopy revealed that electron-dense precursor material (possibly chitin) was present, bathing the microvilli during the first 12 h after blood feeding. This secretion appeared to originate from the bases of the microvilli. From 1 to 36 h, an electron-lucid precursor material (possibly protein) was secreted from the entire length of microvilli and from their bases. Both precursors appeared to be formed at the epithelial surface, not associated with secretory vesicles. The envelope developed rapidly from precursor material, and by 6 h a defined electron-lucid structure was present above the microvilli. Most mature envelopes (12-36 h) were 0.5-2.1 microns thick, multilayered, wholly electron-lucid, and composed of microfibrils and granules. Electron-dense components were seen in some envelopes at 24-36 h. An anterior hyaline plug was present from 12 to 36 h. Envelopes were composed of chitin, protein, and glycoprotein, based on chemical and histochemical tests. The likely presence of several amino acids (lysine, aspartic acid, and glutamic acid) that may cross-link chitin and protein was demonstrated by a positive ninhydrin-Schiff test. This study constitutes the first ultrastructural investigation of peritrophic envelope development by a New World sand fly.

Animals↗
PubMed1995

Insect densoviruses may be widespread in mosquito cell lines.

A diagnostic PCR assay was designed based on conserved regions of previously sequenced densovirus genomic DNA isolated from mosquitoes. Application of this assay to different insect cell lines resulted in a number of cases of consistent positive amplification of the predicted size fragment. Positive PCR results were subsequently confirmed to correlate with densovirus infection by both electron microscopy and indirect fluorescent antibody test. In each case the nucleotide sequence of the amplified PCR fragments showed high identity to previously reported densoviruses isolated from mosquitoes. Phylogenetic analysis based on these sequences showed that two of these isolates were examples of new densoviruses. These viruses could infect and replicate in mosquitoes when administered orally or parenterally and these infections were largely avirulent. In one virus/mosquito combination vertical transmission to progeny was observed. The frequency with which these viruses were detected would suggest that they may be quite common in insect cell lines.

Animals↗