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C R Roberts

Publications and source records attributed to C R Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1992

Genetic analysis of HIV-1 isolates from Zambia and an expanded phylogenetic tree for HIV-1.

Geographic variation in the HIV-1 virus is extensive but incompletely documented. We herein report the first genetic characterization of HIV-1 isolates from Zambia. The genomic region encoding the GAG polyprotein has been compared among 22 Zambian isolates and 14 North American isolates using a combination of polymerase chain reaction (PCR) and DNA sequencing methods. The Zambian isolates were similar to one another but distinct from other HIV-1 isolates. They exhibited a characteristic PCR "fingerprint" wherein certain primer combinations were unable to amplify because of mispairing. The sequence of the complete gag gene of three isolates from Zambia has been determined, and phylogenetic tree analysis placed them in a branch distinct from other African isolates and North American isolates. The PCR procedure used here may be widely applicable for genetic characterization of HIV-1.

Base Sequence↗
PubMed1991

Differential antibody responsiveness to p19 gag results in serological discrimination between human T lymphotropic virus type I and type II.

A new algorithm based upon the differential antibody responses to two gag gene products (p19 and p24) of human T lymphotropic virus (HTLV) has been suggested for serologic discrimination of HTLV type I (HTLV-I) and type II (HTLV-II) [Lillihoj et al., 1990]. To evaluate the practical usefulness of this algorithm, serum specimens from HTLV-seropositive individuals whose infection was confirmed by PCR analysis to be HTLV-I (n = 60) or HTLV-II (n = 61) were analyzed by western blot. The intensities of the antibody response to p24gag and p19gag were scored by one individual without prior knowledge of PCR results. According to the algorithm, specimens with p19 greater than or equal to p24 were classified as HTLV-I, whereas specimens with p19 less than p24 were classified as HTLV-II. Of 60 PCR confirmed HTLV-I specimens, 56 had p19 greater than or equal to p24 (93%) while 4 had p19 less than p24. Of 61 PCR confirmed HTLV-II specimens, 56 had p19 less than p24 (92%) and 5 had p19 greater than or equal to p24. The overall accuracy of serologic differentiation when using this algorithm was 92%, as 4 of 60 HTLV-I (7%) and 5 of 61 HTLV-II (8%) could have been wrongly classified. Although the differential antibody response to p19gag and p24gag provides a simple means of serologically distinguishing between HTLV-I and HTLV-II infection in population-based epidemiological studies, in a clinical context more accurate means of confirmation are required. The dominant p19gag responses were mapped to the C-terminus of p19 (p19(102-117)).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1991

Isolation of Rift Valley fever virus from mosquitoes (Diptera: Culicidae) collected during an outbreak in domestic animals in Kenya.

During an outbreak of Rift Valley fever (RVF) in livestock near Lake Naivasha, Rift Valley Province, Kenya, 61,347 mosquitoes (1,287 pools) collected in CO2-baited light traps yielded seven viral isolates. Five isolates of RVF virus were recovered from 18,831 Culex zombaensis Theobald and one from 14,439 Mansonia africana (Theobald). One isolate of a Bunyamwera group virus was recovered from 1,175 Aedes quasiunivittatus (Theobald).

Animals↗
PubMed1991

Species composition of the Anopheles gambiae complex (diptera: Culicidae) at two sites in western Kenya.

At two sites in the Kisumu area of western Kenya, the species composition of the Anopheles gambiae complex was determined by analysis of ovarian polytene chromosomes. Of 1,915 females, 26.1% were An. arabiensis Patton and 73.9% were An. gambiae Giles; one arabiensis x gambiae hybrid was identified. No major differences in the proportions of An. arabiensis and An. gambiae were observed between sites or between years. The ratio of An. arabiensis/An. gambiae was 6.7:1 (n = 231) in cow-baited traps, 0.2:1 (n = 1,525) in indoor resting samples, and 0.5:1 (n = 145) in all-night human bait catches. The proportion of An. arabiensis decreased progressively from 50.0% to 8.3% (n = 1,129) during 11 wk from September to November 1987; this change was correlated negatively with night temperature and positively with temperature range. In cow-baited traps, 97.4% (n = 194) of An. arabiensis were cow-fed and 95.8% (n = 1,054) of An. gambiae from indoor resting collections were human-fed. In indoor collections, 37.2% (n = 215) of An. arabiensis were cow-fed and 23.1% (n = 26) of An. gambiae from cow traps were human-fed. This demonstrates post-blood-feeding endophily by An. arabiensis and suggests post-blood-feeding exophily by An. gambiae. Malaria infection rates were higher for An. gambiae than for An. arabiensis by a ratio of 3:1 in 1986 (by Plasmodium falciparum ELISA) and 2.3:1 in 1987 (by dissection). Despite the higher proportion of infective An. gambiae, both species in this area serve as efficient vectors through their remarkably stable contact with the human population as demonstrated by their blood feeding and resting behavior.

Animals↗
PubMed1991

Plasmodium species identification by ELISA for sporozoites removed from dried dissection slides.

This study tested the feasibility of identifying salavary gland sporozoites to species by Plasmodium falciparum ELISA by drying them on slides or in vials. The glands were dissected from Anopheles gambiae Giles s.l. and An. funestus Giles collected in western Kenya. In 119 gland infections containing a geometric mean of 1,222 sporozoites, a mean of 72.5% of sporozoites were removed in 60 microliters saline from slides at the time of dissection. Each of the 119 samples was divided into three 18 microliters aliquots. Subsamples were stored at -70 degrees C, dried in vials, or dried on a microslide. When tested by Plasmodium falciparum ELISA, positive reactions were observed in 86.6% of frozen samples, 70.6% of samples held dry in vials, and 50.4% of samples held dry on microslides for 1 mo. Of 90 gland infections where coverslips were removed and slides were left to dry for 1 mo before adding blocking buffer, 81.1% were positive for P. falciparum. This was not significantly different from either frozen gland samples (where 85.5% of 392 infections were identified or frozen gland plus corresponding thorax samples where 86.2% of 160 samples were identified). In malaria field studies, where it is not always practical to freeze samples, sporozoites from dissected mosquitoes can be preserved adequately for ELISA identification by simply removing coverslips and drying dissection slides.

Animals↗
PubMed1991

Quantitation of malaria sporozoites in the salivary glands of wild Afrotropical Anopheles.

The number of malaria sporozoites in the salivary glands was determined microscopically for 1137 wild, naturally infected Anopheles from western Kenya. Infective Anopheles gambiae Giles sensu lato (n = 874) contained a geometric mean (GM) of 962 sporozoites and An.funestus Giles (n = 263) contained 812. No significant differences were detected in geometric mean numbers of sporozoites between species, collection techniques or sites. Of the infective An.gambiae, 1.7% (15/874) contained more than 41,830 sporozoites, the maximum observed for An.funestus. Microscopic techniques were found to be more sensitive than enzyme-linked immunosorbent assays (ELISA) for detecting low-grade sporozoite infections in salivary glands. Salivary gland sporozoites from 83.6% of the 1137 gland infections were identified by ELISA as either Plasmodium falciparum Welch (n = 910), P.ovale Stephens (n = 7), P.malariae Grassi & Feletti (n = 3) or mixed (n = 30). The 187 gland infections which could not be identified by ELISA contained significantly fewer sporozoites (GM = 242) than those which could be identified (GM = 1200).

Animals↗
PubMed1991

Quantitation of malaria sporozoites transmitted in vitro during salivation by wild Afrotropical Anopheles.

The malaria transmission potential of wild, infective Anopheles from western Kenya was evaluated by determining the number of sporozoites transmitted in vitro by salivation when their mouthparts were inserted into capillary tubes containing either sucrose or blood. With sucrose, 86.6% of 102 infective Anopheles transmitted a geometric mean (GM) of 3.84 sporozoites (range 1-34). With blood, 23.1% of 104 infective Anopheles, tested on the day of collection, transmitted a GM of 2.30 sporozoites (range 1-117). For Anopheles held 5 days postcapture before testing with blood, 53.6% of 56 transmitted a GM of 6.04 sporozoites (range 1-420). Transmitting Anopheles contained significantly more salivary gland sporozoites than non-transmitters. No significant differences were detected between Anopheles gambiae Giles sensu lato and Anopheles funestus Giles in sporozoite transmission by individuals with sporozoites in their salivary glands. Sporozoites were detected microscopically in the salivary duct from heads in 80.3% of 117 infective Anopheles (GM = 11.2, range 1-71). Sporozoite detection in mosquito heads by ELISA was 25% less efficient than microscopic detection. Over 98% of the infective Anopheles transmitted less than twenty-five Over 98% of the infective Anopheles transmitted less than twenty-five sporozoites. Transmitted sporozoites represented only about 3% of the total sporozoites in the salivary glands suggesting that sporozoite transmission may be restricted to sporozoites in the salivary duct at the time of feeding. Results are discussed in relation to anti-sporozoite vaccine development.

Animals↗
PubMed1991

Composition changes in human tracheal cartilage in growth and aging, including changes in proteoglycan structure.

High-buoyant-density proteoglycans were extracted and purified from tracheal cartilage obtained from nine individuals aged 1-58 yr. Cartilage from young individuals contained one major species of extractable aggregating proteoglycan and very little link protein. Link protein concentration relative to proteoglycan was observed to increase during the first 14 years of life, consistent with the increased formation of proteoglycan aggregates that are stabilized by link protein, as the process of tracheal cartilage growth and airway lumen widening ends. With increasing age after maturity, two further populations of proteoglycans became more abundant; these were characterized by higher mobility in composite agarose-polyacrylamide gel electrophoresis. The ability of the proteoglycans to associate with hyaluronan decreased with increasing age, although members of each of the three proteoglycan species contained functional hyaluronan-binding domains. Link proteins showed evidence of increasing proteolysis with age. Hydroxyproline content of the cartilage decreased with age; total tissue glycosaminoglycan and water contents showed no significant changes. Altered proteoglycan charge density, proteoglycan size, and aggregation properties, as well as changes in distribution of proteoglycans, may contribute to the changes in cartilage biomechanics that are associated with age-dependent changes in human lung function.

Adolescent↗
PubMed1991

Concurrent infection with Leishmania donovani and Leishmania major in a Kenyan patient: clinical description and parasite characterization.

Leishmania isolates aspirated a few months apart from the spleen of an indigenous adult male kala-azar patient from Baringo District, Kenya, were biochemically characterized and compared. The patient lived within a dual focus of L. donovani kalazar and L. major cutaneous leishmaniasis. A primary Leishmania isolate from splenic aspirates was cryopreserved (NLB-294). The patient was treated with sodium stibogluconate for kala-azar and discharged. Three months later, he had clinical relapse and returned for retreatment. During his second visit, the patient participated in a diagnostic study in which urine and nasopharyngeal samples were cultured for leishmaniasis. Urine, nasopharyngeal, and splenic samples were positive for Leishmania. Secondary isolates from splenic (NLB-294-I) and urine (NLB-318) cultures were cryopreserved and characterized by cellulose acetate electrophoresis (CAE) using 20 enzymes. Whereas the urine isolate was typed as L. donovani, the splenic aspirate culture revealed a mixed infection with L. donovani and L. major. The primary isolate (NLB-294) was then characterized and also showed a mixed infection. To exclude the possibility of protein post-translational modifications in electrophoretic assays, the primary and secondary isolates were grown and processed under identical cultural and lysis conditions, and compared using CAE. The results were identical to the first electrophoretic assays showing mixed promastigote banding patterns. Stationary-phase promastigotes of the secondary splenic isolate (NLB-294-I) inoculated subcutaneously, intraperitoneally, and intracardially into Syrian hamsters and BALB/c mice produced both kala-azar and cutaneous leishmaniasis within 6.5 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Low prevalence of human immunodeficiency virus-1 (HIV-1), HIV-2, and human T cell lymphotropic virus-1 infection in Somalia.

A seroepidemiologic survey was conducted to determine the prevalence of human immunodeficiency virus type 1 (HIV-1), HIV-2, human T cell lymphotropic virus type I (HTLV-I), and Treponema pallidum infection among southern Somalis. Sera were collected from 1,269 study subjects in the urban area of the capital city, Mogadishu, and in the rural towns of Merka, Qoryoley, and Kismayo. The subjects included 57 prostitutes, 79 sexually transmitted disease (STD) patients, and 1,133 others, including outpatient and hospitalized patients with leprosy, tuberculosis, other infectious diseases, individuals from rehabilitation camps and secondary schools, and Ethiopian immigrants. Results indicated that none of the sera were positive for HIV-1 and HIV-2 by Western blot, but one was positive for HTLV-I. The prostitutes had a significantly higher prevalence of treponemal antibody (50.8%; P less than 0.0001) than either the STD patients (12.6%) or the other subjects (5.2%). Epidemiologic data indicated that 94% of the males and females were circumcised and only 2.6% of the males used condoms. Overall, the results of this study suggested a very low prevalence of HIV-1, HIV-2, and HTLV-I infections, especially among prostitutes and STD patients, who were considered at greatest risk of contracting these retroviral infections.

Adolescent↗
PubMed1991

Laboratory diagnosis of retroviral infections.

The molecular biology techniques that were once the exclusive domain of the basic researcher are now becoming apparent within the diagnostic laboratory. Techniques that can detect and quantify the specific genes of retroviruses without the need for radioactive compounds are becoming a reality. In addition, they are rapidly being applied to other viral and nonviral infectious diseases. For the present, techniques that detect the presence of antiretroviral antibodies are the front-line tests for screening and detecting infected, mostly asymptomatic individuals. As vaccines and chemotherapies become the standard of care, tissue culture, PCR, in situ hybridization, and flow cytometry will become the core diagnostic technologies that will enable an accurate prognosis of disease and evaluation of therapy; however, as with any diagnostic procedures, they must be performed against a background of a strong and aggressive quality control and assurance program.

AIDS Serodiagnosis↗
PubMed1991

Mosquito species collected from a marsh in western Kenya during the long rains.

A total of 475,431 mosquitoes representing 8 genera and 43 species were collected from a marsh in the western Kenya highlands to determine species composition and succession in relation to the epidemiology of Rift Valley fever virus. Culex pipiens was the most common species, totalling 92.3% of the collection, followed by Cx. zombaensis (2.2%), Anopheles coustani (1.1%), An. squamosus (0.8%), Mansonia uniformis (0.6%), Coquillettidia microannulatus (0.5%), Uranotaenia mashonaensis (0.5%), Ma. africana (0.4%) and Cq. aurites (0.4%). Aedes quasiunivittatus was the first floodwater species to emerge from newly flooded areas and was the most abundant Aedes collected, representing 88% of all Aedes specimens. Culex guiarti and Cx. zombaensis colonized newly flooded areas soon after the areas became flooded.

Aedes↗
PubMed1991

Egg hatching of Aedes mosquitoes during successive floodings in a Rift Valley fever endemic area in Kenya.

Floodwater Aedes breeding habitats in central Kenya were sequentially flooded to determine the numbers of mosquito eggs hatching during each flooding. Approximately 90% of the larvae sampled during 4 floodings emerged during the initial flooding. The number of Aedes eggs hatching during the second flooding was lowest of all 4 floodings, and no significant differences in the amount of egg hatching during floodings 3 and 4 were seen. Unhatched Aedes eggs were present in soil samples collected after the final flooding. The possible implications of these findings with regard to Rift Valley fever virus control are discussed.

Aedes↗
PubMed1990

Malaria sporozoite detection by dissection and ELISA to assess infectivity of afrotropical Anopheles (Diptera: Culicidae).

Malaria infection rates determined by dissection and Plasmodium falciparum enzyme-linked immunosorbent assay (ELISA) were compared for 26,935 Anopheles gambiae Giles sensu lato and 17,739 Anopheles funestus Giles collected during 20 mo in western Kenya. ELISA infection rates were about 43% higher than dissection sporozoite rates. In dissection-negative Anopheles, circumsporozoite (CS) protein was detected by ELISA in 5.2% of 10,017 salivary gland samples and in 12.2% of 237 thorax samples. The accuracy of dissection and ELISA techniques was compared by the following tests on a group of 352 field-collected Anopheles (held 10 d to ensure sporogonic development): salivary gland dissection, examination of Giemsa-stained dissection slides, ELISA tests on salivary gland and thorax body parts, and microscopic techniques for determining sporozoite loads. Respective infection rates were 9.9%, 10.8%, and 15.6% for dissection, stained slides, and ELISA. Sporozoite loads were associated significantly with ELISA absorbance values (r = 0.76). Compared with Giemsa-stained dissection slide results, the sensitivity of sporozoite detection was 92.1% for dissection compared with 78.9% for ELISA; specificity was 100.0% for dissection versus 92.0% for ELISA. Immunological detection of CS protein in head-thorax samples of Afrotropical vectors overestimated the proportion of infective Anopheles because the comparison of techniques indicated that 45.4% of the ELISA positive Anopheles did not contain salivary gland sporozoites.

Animals↗
PubMed1990

Characterization of malaria transmission by Anopheles (Diptera: Culicidae) in western Kenya in preparation for malaria vaccine trials.

Malaria transmission was studied for 33 mo in the villages of Kisian and Saradidi in western Kenya in preparation for field trials of malaria vaccines. Abundance estimates of Anopheles gambiae Giles sensu lato and Anopheles funestus Giles, which constituted over 99% of 26,645 anophelines collected, were compared for all-night biting collections inside houses, outdoors, and in tents. The overall numbers of Anopheles per man-night were 2.3 times greater in Kisian than in Saradidi. For the three types of collections, mean sporozoite rates by dissection ranged from 2.2 to 5.4% for 13,072 Anopheles in Kisian and from 9.9 to 13.6% for 7,058 Anopheles in Saradidi; greater than 90% of the infections were Plasmodium falciparum, either alone or mixed with P. malariae or P. ovale. Heaviest transmission from April to July coincided with the end of the long rainy season. Entomological inoculation rates (EIR) averaged 0.82 infective bites per man per night inside houses in Kisian and 0.65 in Saradidi. Outdoors, EIRs averaged 0.09 in Kisian and 0.52 in Saradidi. In tents, which were evaluated to identify methods for exposing nonindigenous volunteers during vaccine efficacy trials, EIRs were 3.3 and 2.5 times less than inside houses for Kisian (EIR = 0.25) and Saradidi (EIR = 0.26), respectively. Exposure in tents averaged one infective bite every 4.0 d in Kisian and every 3.8 d in Saradidi. The use of tents in vaccine efficacy trials should provide adequate exposure for nonindigenous volunteers. Malaria vaccine trials could be conducted efficiently in western Kenya, with timing dependent upon the intensity of transmission required by vaccine trial objectives.

Analysis of Variance↗
PubMed1990

Interpretation of low-level Plasmodium infection rates determined by ELISA for anophelines (Diptera: Culicidae) from Egyptian oases.

Plasmodium infection rates determined by enzyme-linked immunosorbent assay (ELISA) were compared for Anopheles sergentii (Theobald) and An. multicolor Cambouliu in Siwa Oasis, Egypt, an area with low-level Plasmodium vivax transmission, and in Bahariya and Farafra, two other Egyptian oases which appear to be free of malaria. Initial testing indicated that 4.4% (23 of 518) and 0.8% (4 of 518) of the An. sergentii were positive for P. vivax and P. falciparum, respectively, and that 1.4% (1 of 71) of the An. multicolor were positive for P. falciparum. However, after two confirmational tests, only 1.2% (6 of 518) of the An. sergentii remained consistently positive for P. vivax. Initial ELISA absorbance was not a useful predictor of potential false positive reactions in the P. vivax assay. Paradoxically, the six ELISA-positive An. sergentii were from the two malaria-free oases. This study raises the question of whether ELISA-positive reactions for anopheline vector species provides unequivocal evidence for transmission in areas of low malaria endemicity.

Animals↗
PubMed1990

Development of Leishmania major in Phlebotomus duboscqi and Sergentomyia schwetzi (Diptera: Psychodidae).

The extrinsic development of Leishmania major was observed in 2 man-biting sand flies, Phlebotomus duboscqi, a known vector, and Sergentomyia schwetzi, an assumed non-vector. Flies fed on a leishmanial lesion on the nose of a hamster were examined for infection at 0, 6, 12, 18, 24, 36, 48, and 60 hr and at approximately 24 hr intervals from day 3 to day 14 post-feeding. Infection rates, determined by light microscopy, were 47% (n = 258) in P. duboscqi and 5% (n = 162) in S. schwetzi. Transformation from amastigotes to "procyclic" promastigotes occurred in both species at 6-18 hr post-feeding. In P. duboscqi, the parasites multiplied rapidly and developed through as many as 10 forms, including at least 3 dividing-promastigote forms. Metacyclic promastigotes, the "infective" form, appeared at 6 days post-feeding, first in the region of the stomodeal valve, then in the pharynx, cibarium, and proboscis. In a single attempt 14 days post-feeding, a P. duboscqi transmitted L. major to a mouse by bite. In contrast, the parasites multiplied slowly in S. schwetzi, and did not develop beyond "procyclic" promastigotes. The parasites did not migrate anteriorly nor survive beyond 90 hr post-feeding, indicating that S. schwetzi is not a vector of L. major. Classical strategies for vector incrimination may be confounded by the isolation of non-infective early developmental forms of Leishmania from wild-caught non-vectors.

Animals↗