medRxiv (Cold Spring Harbor Laboratory), Mar 18, 2024
Human milk oligosaccharides (HMOs), whose compositions vary between secretor and non-secretor mot... more Human milk oligosaccharides (HMOs), whose compositions vary between secretor and non-secretor mothers, protect breastfeeding children against various diseases. We investigated the relationship between HMOs in Ugandan secretor mothers and malaria outcomes in their children. Malaria outcomes in breastfeeding children followed up over seven months were classified as malaria-free and asymptomatic, mild, or severe malaria. A single human milk sample collected from each mother was analyzed for HMOs. Significantly higher 2'fucosyllactose (2'FL) and lacto-N-fucopentaose I (LNFP I) concentrations were observed in mothers of malaria-free children, and significantly higher lacto-N-tetraose (LNT) concentrations were observed in mothers of children with asymptomatic malaria. Concentrations of five HMOs, 3-All rights reserved. No reuse allowed without permission.
The proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfi... more The proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfilaraemic (Mf þ) subjects infected by Loa loa in response to antigens of several parasitic stages were compared with those from amicrofilaraemic (Mf ¹) individuals. While a strong lymphoproliferative response and consistent levels of both Th1 (IL-2, interferon-gamma (IFN-g)) and Th2 (IL-4, IL-5) type cytokines were observed in response to adult worm (AW) and microfilariae (Mf) antigen in Mf ¹ individuals, Mf þ subjects were characterized by a T cell unresponsiveness, including proliferation, cytokine production and IL-2 mRNA expression. Conversely, T cell responsiveness to mitogens and non-specific antigen were similar in the two endemic populations. Depletion of lymphocyte subpopulations indicated that T CD4 þ were mainly involved in the specific cellular response. In contrast to other cytokines, IL-10 was produced in response to all parasitic stages, in both Mf þ and Mf ¹ patients. Neutralization of IL-10 did not restore cytokine production in Mf þ patients, while B7 mRNA expression was similar between Mf þ and Mf ¹ subjects in response to Mf antigen, suggesting that IL-10 was not the only factor responsible for T cell unresponsiveness. Mf þ patients have lower Mf antigen-specific IgG levels compared with Mf ¹ , and there is a significant correlation between Mf antigen-specific antibodies and IL-5 responses. These findings suggest that Mf ¹ status is correlated with T helper responsiveness, including proliferation and production of both Th1-and Th2-type cytokines, whereas Mf þ status is characterized by unresponsiveness of the same cell population, induced and/or maintained by microfilariae.
A partial cDNA clone encoding a putative nicotinic acetylcholine receptor (ACHR) subunit of the h... more A partial cDNA clone encoding a putative nicotinic acetylcholine receptor (ACHR) subunit of the human filarial parasite, Onchocerca vo1vulus, has been isolated and sequenced. A truncated open reading frame of 1308 bp capable of encoding 436 amino acids with a calculated M, of 51209 was identified. The absence of the double cysteine residues necessary for neurotransmitter binding indicates that the cloned ACHR is a non-a subunit.
American Journal of Tropical Medicine and Hygiene, Jul 1, 1990
Tropical pulmonary eosinophilia (TPE) is believed to result from extreme immediate hypersensitivi... more Tropical pulmonary eosinophilia (TPE) is believed to result from extreme immediate hypersensitivity to microfilariae localized in the pulmonary vasculature of some persons with lymphatic filariasis. Female BALB/c mice repeatedly immunized by ip injection of Brugia malayi microfilariae become amicrofilaremic within 24 hr of iv parasite challenge, whereas non-sensitized control animals remain patent for greater than 72 hr. Immunized, but not control mice, develop peripheral blood and pulmonary eosinophilia (2,000 cells/mm3 and 65,000 cells/bronchoalveolar lavage, respectively). Serum and bronchoalveolar lavage filarial-specific IgG antibodies are greater in sensitized mice than in controls (ELISA absorbance values 20- and 10-fold higher, respectively). Serum IgE antibody levels are also greater (P less than 0.01) in immunized parasite-challenged mice than in controls (mean cpm 125I-labeled anti-mouse IgE bound to B. malayi antigen-coated Sepharose beads: 7,852 vs. 1,741, respectively). This model exhibits several of the major features of human TPE: amicrofilaremia, elevated levels of serum IgG and IgE antibodies to microfilariae, and blood and pulmonary eosinophilia. This model may be useful in the examination of the role of filarial antigen-specific lymphoid cells and antibodies in regulating the pathologic responses to microfilariae trapped in the lung.
Cassava (Manihot esculenta Crantz) is a starchy root crop grown in the tropics mainly by small-sc... more Cassava (Manihot esculenta Crantz) is a starchy root crop grown in the tropics mainly by small-scale farmers even though agro-industrial processing is rapidly increasing. For this processing market improved varieties with high dry matter root content (DMC) is required. Potentially toxic cyanogenic glucosides are synthesized in the leaves and translocated to the roots. Selection for varieties with low cyanogenic glucoside potential (CNP) and high DMC is among the principal objectives in cassava breeding programs. However, these traits are highly influenced by the environmental conditions and the genetic control of these traits is not well understood. An S(1) population derived from a cross between two bred cassava varieties (MCOL 1684 and Rayong 1) that differ in CNP and DMC was used to study the heritability and genetic basis of these traits. A broad-sense heritability of 0.43 and 0.42 was found for CNP and DMC, respectively. The moderate heritabilities for DMC and CNP indicate that the phenotypic variation of these traits is explained by a genetic component. We found two quantitative trait loci (QTL) on two different linkage groups controlling CNP and six QTL on four different linkage groups controlling DMC. One QTL for CNP and one QTL for DMC mapped near each other, suggesting pleiotrophy and/or linkage of QTL. The two QTL for CNP showed additive effects while the six QTL for DMC showed additive effect, dominance or overdominance. This study is a first step towards developing molecular marker tools for efficient breeding of CNP and DMC in cassava.
The objectives of the present study were to identify and characterize biochemically the major ant... more The objectives of the present study were to identify and characterize biochemically the major antigens of Brugia malayi microfilariae, a filarial parasite that infects humans. IgG antibodies in sera of mice which had cleared parasites from the bloodstream reacted with 30, 55, 94 and 150 kDa molecules of living microfilariae radioiodinated by the Iodo-bead method. Sera of humans infected with the related filariae Wuchereria bancrofti, Loa loa or Onchocerca volvulus immunoprecipitated molecules of similar size as well as two additional proteins of 22 and 43 kDa. Sera of uninfected North Americans or mice infected with Trichinella spiralis or Schistosoma mansoni did not recognize these radioiodinated antigens. Experiments to examine the possible surface localization and metabolism of these antigens showed that they were removed from intact parasites exposed to chymotrypsin or trypsin and that immunogenic molecules of 30, 55, and 150 kDa were released into excretory-secretory products by viable microfilariae. [35S]Methionine biosynthetically labeled polypeptide antigens of 22, 30, 35 and 150 kDa were detected by antibody reacted with intact microfilariae and/or their excretion products. Antigens of 30, 55, and 150 kDa appear to be glycoproteins as they bound wheat germ agglutinin and were biosynthetically labeled with [14C]N-acetyl-D-glucosamine. These data suggest that the surface of B. malayi microfilariae is a dynamic structure which synthesizes and sheds antigens.
American Journal of Tropical Medicine and Hygiene, Jul 1, 1993
Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmissi... more Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmission zone in Gabon were carried out. Onchocerca volvulus, Loa loa, Mansonella streptocerca, and M. perstans are transmitted in this region. Based on parasitologic findings and age, the 47 individuals were stratified into four groups: microfilaria negative (Mf-) children (3-15 years old), Mf- adults (> 15 years old), microfilaria positive (Mf+) children and Mf+ adults. For descriptive purposes, the term microfilaria positive refers to individuals with skin and blood microfilariae. Antifilarial antibody titers were determined using an enzyme-linked immunosorbent assay with Dipetalonema viteae antigens. In general, children had higher titers of IgG antibodies than adults. For the IgG1, IgG2, and IgG3 subclass responses, both age and microfilarial status appeared to be important variables since Mf- children consistently had the highest titers whereas Mf- adults had the lowest titers. For the IgG4 antifilarial response, only the microfilarial status was an important variable. All Mf+ individuals had significantly higher levels of IgG4 antibody than Mf- individuals. Pooled sera of Mf- and Mf+ individuals reacted with similar O. volvulus antigens on Western blots. Control sera of individuals who did not reside in the study area, but who had single infections with L. loa or M. perstans, did not react with any O. volvulus antigens.
Pre-existing and intervening low-density Plasmodium infections complicate the conduct of malaria ... more Pre-existing and intervening low-density Plasmodium infections complicate the conduct of malaria clinical trials. These infections confound infection detection endpoints, and their immunological effects may detract from intended vaccineinduced immune responses. Historically, these infections were often unrecognized since infrequent and often analytically insensitive parasitological testing was performed before and during trials. Molecular diagnostics now permits their detection, but investigators must weigh the cost, complexity, and personnel demands on the study and the laboratory when scheduling such tests. This paper discusses the effect of pre-existing and intervening, low-density Plasmodium infections on malaria vaccine trial endpoints and the current methods employed for their infection detection. We review detection techniques, that until recently, provided a dearth of cost-effective strategies for detecting low density infections. A recently deployed, field-tested, simple, and cost-effective molecular diagnostic strategy for detecting pre-existing and intervening Plasmodium infections from dried blood spots (DBS) in malaria-endemic settings is discussed to inform new clinical trial designs. Strategies that combine sensitive molecular diagnostic techniques with convenient DBS collections and cost-effective pooling strategies may enable more thorough and informative infection monitoring in upcoming malaria clinical trials and epidemiological studies.
Background Many Plasmodium infections in endemic regions exist at densities below the limit of de... more Background Many Plasmodium infections in endemic regions exist at densities below the limit of detection of standard diagnostic tools. These infections threaten control efforts and may impact vaccine and therapeutic drug studies. Simple, cost-effective methods are needed to study the natural history of asymptomatic submicroscopic parasitaemia. Self-collected dried blood spots (DBS) analysed using pooled and individual quantitative reverse transcription polymerase chain reaction (qRT-PCR) provide such a solution. Here, the feasibility and acceptability of daily at-home DBS collections for qRT-PCR was studied to better understand low-density infections. Methods Rapid diagnostic test (RDT)-negative individuals in Katakwi District, northeastern Uganda, were recruited between April and May 2021. Venous blood samples and clinic-collected DBS were taken at enrollment and at four weekly clinic visits. Participants were trained in DBS collection and asked to collect six DBS weekly between cl...
International Journal of Infectious Diseases, 2021
Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on ... more Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre-including this research content-immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.
Background The development of malaria vaccines is constrained by genetic polymorphisms exhibited ... more Background The development of malaria vaccines is constrained by genetic polymorphisms exhibited by Plasmodium falciparum antigens. The project the age-dependent distribution of alleles or haplotypes of three P. falciparum malaria vaccine candidates, Circumsporozoite Protein (csp), Erythrocyte Binding Antigen 175 (eba-175) and Serine Repeat Antigen 5 (sera5) in a region of intense malaria transmission in Uganda. Methods A cross-sectional study was carried out between August and November 2009 in which 250 study participants were selected from a population of 600. Finger prick blood samples were collected after informed consent from participants below 5 years, 5–10 years, and above 10 years of age. Blood was used for microscopy, RDT and dried blood spots. Plasmodium falciparum DNA was extracted by chelex method. Alleles of sera5 and eba-175 were determined by polymerase chain reaction (PCR) amplification followed by resolution of products by agarose gel electrophoresis. Allele calling...
The American Journal of Tropical Medicine and Hygiene, 2020
The ultrasensitive Alere Plasmodium falciparum Malaria Ag histidine-rich protein 2 rapid diagnost... more The ultrasensitive Alere Plasmodium falciparum Malaria Ag histidine-rich protein 2 rapid diagnostic test (Alere uRDT, Suwon City, South Korea) is a new diagnostic tool which is more expensive than other malaria rapid diagnostic tests (RDTs) routinely used in Ugandan clinics. The manufacturer recommends testing samples within 2 days and scoring results after 20 minutes, which may be impractical in high-volume resource-poor clinics. We compared testing by the Alere Ag rapid diagnostic test (uRDT), CareStart RDT, microscopy, and an ultrasensitive I8S rRNA quantitative reverse transcription polymerase chain reaction (qRT-PCR) using survey and clinical samples. For the Alere uRDT, we used survey blood samples stored at 4°C for 44 days and for some clinical samples deliberately scored results beyond 20 minutes. The Alere uRDT and qRT-PCR identified asymptomatic parasitemia cases in 56% and 72%, respectively, of survey samples originally scored as negative by the CareStart RDT. Using qRT-PCR as a gold standard, the Alere uRDT was superior to the CareStart RDT in estimating asymptomatic parasite prevalence in a cross-sectional survey (P = 0.007) and in detection of clinically significant malaria; both RDTs were comparable in detecting asymptomatic parasitemia in the clinic (P = 0.599). Scoring Alere uRDT results at 20 minutes produced valid results confirmed by the CareStart RDT, but there was a consistent background; scoring the Alere uRDT beyond 20 minutes produced false-positive results. The Alere uRDT outperformed the CareStart RDT (ACCESSBIO, Somerset, NJ) in a field survey in estimating malaria prevalence and in the clinic for symptomatic malarial illness. It produced reliable results using samples stored at 4°C for 44 days, but test results read beyond 20 minutes were invalid.
To establish Plasmodium falciparum malariometric indices in a field study site in Apac district, ... more To establish Plasmodium falciparum malariometric indices in a field study site in Apac district, northern Uganda. A community-based cross sectional survey. Atopi Parish, Apac district, Uganda, 1995. One thousand two hundred and thirty four volunteers aged below one and ninety years. P. falciparum parasitaemia rates and parasite density, splenomegaly, bednet use and chloroquine consumption. All subjects with P. falciparum positive smears were treated with chloroquine. The population prevalence of parasitaemia was 62.1% with the predominant species being P. falciparum (100%) and P. malariae in the minority (3.5%); P. ovale was not seen. The prevalence of parasitaemia in subjects older than 20 years and in those under ten years was 36% and 85%, respectively. The geometric mean parasite density started to decline by the age of six years. The splenomegaly rate in subjects over the age of 12 years and in those under nine years was 19.8% and 63.1%, respectively. Bednet use and chloroquine ...
Annals of Tropical Medicine And Parasitology, 2000
A cross-sectional study of pregnant women was conducted at Nsambya Hospital in Kampala, to invest... more A cross-sectional study of pregnant women was conducted at Nsambya Hospital in Kampala, to investigate the prevalence and effect of Plasmodium falciparum infections during pregnancy, in a peri-urban/urban location. Overall, 544 pregnant women were recruited when they presented at the labour ward for delivery. After giving informed consent, each subject answered a questionnaire and underwent a physical examination, and peripheral-blood samples were obtained. After each uncomplicated delivery, samples of placental and cord blood were obtained from the placenta and infant, respectively, and infant birthweights were recorded. Smears were prepared from the blood samples and checked for parasites. Only 46 and 36 of the 537 women investigated were positive for P. falciparum infection in their peripheral and placental blood, respectively. Plasmodium falciparum was the only parasite encountered. The prevalences of low birthweight and maternal parasitaemia and the intensities of maternal infection were each greater in primigravidae than secundi-or multi-gravidae. Despite the low prevalence of parasitaemia in this population, P. falciparum infection in the primigravidae was a signi® cant contributor to their ill health, leading to low birthweights in their infants.
SE36 antigen, derived from serine repeat antigen 5 (SERA5) of Plasmodium falciparum, is a promisi... more SE36 antigen, derived from serine repeat antigen 5 (SERA5) of Plasmodium falciparum, is a promising blood stage malaria vaccine candidate. Designated as BK-SE36, the SE36 antigen was formulated with aluminum hydroxyl gel (AHG) and produced under Good Manufacturing Practice (GMP) constraints. In a Phase Ib clinical trial and follow-up study in Uganda, the risk for malaria symptoms was reduced by 72% compared with the control group. Although promising, the number of responders to the vaccine in 6-20years-olds was approximately 30% with the majority in the younger cohort. This is in contrast to the phase Ia clinical trial where response to the vaccine was 100% in Japanese malaria naive adults. A consideration that can be of importance is the involvement of host genetic factors that may influence the ability to mount an effective immune response to vaccination as well as susceptibility to malaria infection. We, therefore, analyzed allelic polymorphism of human leukocyte antigen (HLA)-DRB1 alleles using sequence-based typing (SBT). In this study, DRB1 alleles did not influence antibody response to BK-SE36 and the vaccinees susceptibility to clinical malaria.
medRxiv (Cold Spring Harbor Laboratory), Mar 18, 2024
Human milk oligosaccharides (HMOs), whose compositions vary between secretor and non-secretor mot... more Human milk oligosaccharides (HMOs), whose compositions vary between secretor and non-secretor mothers, protect breastfeeding children against various diseases. We investigated the relationship between HMOs in Ugandan secretor mothers and malaria outcomes in their children. Malaria outcomes in breastfeeding children followed up over seven months were classified as malaria-free and asymptomatic, mild, or severe malaria. A single human milk sample collected from each mother was analyzed for HMOs. Significantly higher 2'fucosyllactose (2'FL) and lacto-N-fucopentaose I (LNFP I) concentrations were observed in mothers of malaria-free children, and significantly higher lacto-N-tetraose (LNT) concentrations were observed in mothers of children with asymptomatic malaria. Concentrations of five HMOs, 3-All rights reserved. No reuse allowed without permission.
The proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfi... more The proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfilaraemic (Mf þ) subjects infected by Loa loa in response to antigens of several parasitic stages were compared with those from amicrofilaraemic (Mf ¹) individuals. While a strong lymphoproliferative response and consistent levels of both Th1 (IL-2, interferon-gamma (IFN-g)) and Th2 (IL-4, IL-5) type cytokines were observed in response to adult worm (AW) and microfilariae (Mf) antigen in Mf ¹ individuals, Mf þ subjects were characterized by a T cell unresponsiveness, including proliferation, cytokine production and IL-2 mRNA expression. Conversely, T cell responsiveness to mitogens and non-specific antigen were similar in the two endemic populations. Depletion of lymphocyte subpopulations indicated that T CD4 þ were mainly involved in the specific cellular response. In contrast to other cytokines, IL-10 was produced in response to all parasitic stages, in both Mf þ and Mf ¹ patients. Neutralization of IL-10 did not restore cytokine production in Mf þ patients, while B7 mRNA expression was similar between Mf þ and Mf ¹ subjects in response to Mf antigen, suggesting that IL-10 was not the only factor responsible for T cell unresponsiveness. Mf þ patients have lower Mf antigen-specific IgG levels compared with Mf ¹ , and there is a significant correlation between Mf antigen-specific antibodies and IL-5 responses. These findings suggest that Mf ¹ status is correlated with T helper responsiveness, including proliferation and production of both Th1-and Th2-type cytokines, whereas Mf þ status is characterized by unresponsiveness of the same cell population, induced and/or maintained by microfilariae.
A partial cDNA clone encoding a putative nicotinic acetylcholine receptor (ACHR) subunit of the h... more A partial cDNA clone encoding a putative nicotinic acetylcholine receptor (ACHR) subunit of the human filarial parasite, Onchocerca vo1vulus, has been isolated and sequenced. A truncated open reading frame of 1308 bp capable of encoding 436 amino acids with a calculated M, of 51209 was identified. The absence of the double cysteine residues necessary for neurotransmitter binding indicates that the cloned ACHR is a non-a subunit.
American Journal of Tropical Medicine and Hygiene, Jul 1, 1990
Tropical pulmonary eosinophilia (TPE) is believed to result from extreme immediate hypersensitivi... more Tropical pulmonary eosinophilia (TPE) is believed to result from extreme immediate hypersensitivity to microfilariae localized in the pulmonary vasculature of some persons with lymphatic filariasis. Female BALB/c mice repeatedly immunized by ip injection of Brugia malayi microfilariae become amicrofilaremic within 24 hr of iv parasite challenge, whereas non-sensitized control animals remain patent for greater than 72 hr. Immunized, but not control mice, develop peripheral blood and pulmonary eosinophilia (2,000 cells/mm3 and 65,000 cells/bronchoalveolar lavage, respectively). Serum and bronchoalveolar lavage filarial-specific IgG antibodies are greater in sensitized mice than in controls (ELISA absorbance values 20- and 10-fold higher, respectively). Serum IgE antibody levels are also greater (P less than 0.01) in immunized parasite-challenged mice than in controls (mean cpm 125I-labeled anti-mouse IgE bound to B. malayi antigen-coated Sepharose beads: 7,852 vs. 1,741, respectively). This model exhibits several of the major features of human TPE: amicrofilaremia, elevated levels of serum IgG and IgE antibodies to microfilariae, and blood and pulmonary eosinophilia. This model may be useful in the examination of the role of filarial antigen-specific lymphoid cells and antibodies in regulating the pathologic responses to microfilariae trapped in the lung.
Cassava (Manihot esculenta Crantz) is a starchy root crop grown in the tropics mainly by small-sc... more Cassava (Manihot esculenta Crantz) is a starchy root crop grown in the tropics mainly by small-scale farmers even though agro-industrial processing is rapidly increasing. For this processing market improved varieties with high dry matter root content (DMC) is required. Potentially toxic cyanogenic glucosides are synthesized in the leaves and translocated to the roots. Selection for varieties with low cyanogenic glucoside potential (CNP) and high DMC is among the principal objectives in cassava breeding programs. However, these traits are highly influenced by the environmental conditions and the genetic control of these traits is not well understood. An S(1) population derived from a cross between two bred cassava varieties (MCOL 1684 and Rayong 1) that differ in CNP and DMC was used to study the heritability and genetic basis of these traits. A broad-sense heritability of 0.43 and 0.42 was found for CNP and DMC, respectively. The moderate heritabilities for DMC and CNP indicate that the phenotypic variation of these traits is explained by a genetic component. We found two quantitative trait loci (QTL) on two different linkage groups controlling CNP and six QTL on four different linkage groups controlling DMC. One QTL for CNP and one QTL for DMC mapped near each other, suggesting pleiotrophy and/or linkage of QTL. The two QTL for CNP showed additive effects while the six QTL for DMC showed additive effect, dominance or overdominance. This study is a first step towards developing molecular marker tools for efficient breeding of CNP and DMC in cassava.
The objectives of the present study were to identify and characterize biochemically the major ant... more The objectives of the present study were to identify and characterize biochemically the major antigens of Brugia malayi microfilariae, a filarial parasite that infects humans. IgG antibodies in sera of mice which had cleared parasites from the bloodstream reacted with 30, 55, 94 and 150 kDa molecules of living microfilariae radioiodinated by the Iodo-bead method. Sera of humans infected with the related filariae Wuchereria bancrofti, Loa loa or Onchocerca volvulus immunoprecipitated molecules of similar size as well as two additional proteins of 22 and 43 kDa. Sera of uninfected North Americans or mice infected with Trichinella spiralis or Schistosoma mansoni did not recognize these radioiodinated antigens. Experiments to examine the possible surface localization and metabolism of these antigens showed that they were removed from intact parasites exposed to chymotrypsin or trypsin and that immunogenic molecules of 30, 55, and 150 kDa were released into excretory-secretory products by viable microfilariae. [35S]Methionine biosynthetically labeled polypeptide antigens of 22, 30, 35 and 150 kDa were detected by antibody reacted with intact microfilariae and/or their excretion products. Antigens of 30, 55, and 150 kDa appear to be glycoproteins as they bound wheat germ agglutinin and were biosynthetically labeled with [14C]N-acetyl-D-glucosamine. These data suggest that the surface of B. malayi microfilariae is a dynamic structure which synthesizes and sheds antigens.
American Journal of Tropical Medicine and Hygiene, Jul 1, 1993
Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmissi... more Immunologic analyses of sera from 47 selected individuals living in a mixed filariasis transmission zone in Gabon were carried out. Onchocerca volvulus, Loa loa, Mansonella streptocerca, and M. perstans are transmitted in this region. Based on parasitologic findings and age, the 47 individuals were stratified into four groups: microfilaria negative (Mf-) children (3-15 years old), Mf- adults (> 15 years old), microfilaria positive (Mf+) children and Mf+ adults. For descriptive purposes, the term microfilaria positive refers to individuals with skin and blood microfilariae. Antifilarial antibody titers were determined using an enzyme-linked immunosorbent assay with Dipetalonema viteae antigens. In general, children had higher titers of IgG antibodies than adults. For the IgG1, IgG2, and IgG3 subclass responses, both age and microfilarial status appeared to be important variables since Mf- children consistently had the highest titers whereas Mf- adults had the lowest titers. For the IgG4 antifilarial response, only the microfilarial status was an important variable. All Mf+ individuals had significantly higher levels of IgG4 antibody than Mf- individuals. Pooled sera of Mf- and Mf+ individuals reacted with similar O. volvulus antigens on Western blots. Control sera of individuals who did not reside in the study area, but who had single infections with L. loa or M. perstans, did not react with any O. volvulus antigens.
Pre-existing and intervening low-density Plasmodium infections complicate the conduct of malaria ... more Pre-existing and intervening low-density Plasmodium infections complicate the conduct of malaria clinical trials. These infections confound infection detection endpoints, and their immunological effects may detract from intended vaccineinduced immune responses. Historically, these infections were often unrecognized since infrequent and often analytically insensitive parasitological testing was performed before and during trials. Molecular diagnostics now permits their detection, but investigators must weigh the cost, complexity, and personnel demands on the study and the laboratory when scheduling such tests. This paper discusses the effect of pre-existing and intervening, low-density Plasmodium infections on malaria vaccine trial endpoints and the current methods employed for their infection detection. We review detection techniques, that until recently, provided a dearth of cost-effective strategies for detecting low density infections. A recently deployed, field-tested, simple, and cost-effective molecular diagnostic strategy for detecting pre-existing and intervening Plasmodium infections from dried blood spots (DBS) in malaria-endemic settings is discussed to inform new clinical trial designs. Strategies that combine sensitive molecular diagnostic techniques with convenient DBS collections and cost-effective pooling strategies may enable more thorough and informative infection monitoring in upcoming malaria clinical trials and epidemiological studies.
Background Many Plasmodium infections in endemic regions exist at densities below the limit of de... more Background Many Plasmodium infections in endemic regions exist at densities below the limit of detection of standard diagnostic tools. These infections threaten control efforts and may impact vaccine and therapeutic drug studies. Simple, cost-effective methods are needed to study the natural history of asymptomatic submicroscopic parasitaemia. Self-collected dried blood spots (DBS) analysed using pooled and individual quantitative reverse transcription polymerase chain reaction (qRT-PCR) provide such a solution. Here, the feasibility and acceptability of daily at-home DBS collections for qRT-PCR was studied to better understand low-density infections. Methods Rapid diagnostic test (RDT)-negative individuals in Katakwi District, northeastern Uganda, were recruited between April and May 2021. Venous blood samples and clinic-collected DBS were taken at enrollment and at four weekly clinic visits. Participants were trained in DBS collection and asked to collect six DBS weekly between cl...
International Journal of Infectious Diseases, 2021
Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on ... more Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre-including this research content-immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.
Background The development of malaria vaccines is constrained by genetic polymorphisms exhibited ... more Background The development of malaria vaccines is constrained by genetic polymorphisms exhibited by Plasmodium falciparum antigens. The project the age-dependent distribution of alleles or haplotypes of three P. falciparum malaria vaccine candidates, Circumsporozoite Protein (csp), Erythrocyte Binding Antigen 175 (eba-175) and Serine Repeat Antigen 5 (sera5) in a region of intense malaria transmission in Uganda. Methods A cross-sectional study was carried out between August and November 2009 in which 250 study participants were selected from a population of 600. Finger prick blood samples were collected after informed consent from participants below 5 years, 5–10 years, and above 10 years of age. Blood was used for microscopy, RDT and dried blood spots. Plasmodium falciparum DNA was extracted by chelex method. Alleles of sera5 and eba-175 were determined by polymerase chain reaction (PCR) amplification followed by resolution of products by agarose gel electrophoresis. Allele calling...
The American Journal of Tropical Medicine and Hygiene, 2020
The ultrasensitive Alere Plasmodium falciparum Malaria Ag histidine-rich protein 2 rapid diagnost... more The ultrasensitive Alere Plasmodium falciparum Malaria Ag histidine-rich protein 2 rapid diagnostic test (Alere uRDT, Suwon City, South Korea) is a new diagnostic tool which is more expensive than other malaria rapid diagnostic tests (RDTs) routinely used in Ugandan clinics. The manufacturer recommends testing samples within 2 days and scoring results after 20 minutes, which may be impractical in high-volume resource-poor clinics. We compared testing by the Alere Ag rapid diagnostic test (uRDT), CareStart RDT, microscopy, and an ultrasensitive I8S rRNA quantitative reverse transcription polymerase chain reaction (qRT-PCR) using survey and clinical samples. For the Alere uRDT, we used survey blood samples stored at 4°C for 44 days and for some clinical samples deliberately scored results beyond 20 minutes. The Alere uRDT and qRT-PCR identified asymptomatic parasitemia cases in 56% and 72%, respectively, of survey samples originally scored as negative by the CareStart RDT. Using qRT-PCR as a gold standard, the Alere uRDT was superior to the CareStart RDT in estimating asymptomatic parasite prevalence in a cross-sectional survey (P = 0.007) and in detection of clinically significant malaria; both RDTs were comparable in detecting asymptomatic parasitemia in the clinic (P = 0.599). Scoring Alere uRDT results at 20 minutes produced valid results confirmed by the CareStart RDT, but there was a consistent background; scoring the Alere uRDT beyond 20 minutes produced false-positive results. The Alere uRDT outperformed the CareStart RDT (ACCESSBIO, Somerset, NJ) in a field survey in estimating malaria prevalence and in the clinic for symptomatic malarial illness. It produced reliable results using samples stored at 4°C for 44 days, but test results read beyond 20 minutes were invalid.
To establish Plasmodium falciparum malariometric indices in a field study site in Apac district, ... more To establish Plasmodium falciparum malariometric indices in a field study site in Apac district, northern Uganda. A community-based cross sectional survey. Atopi Parish, Apac district, Uganda, 1995. One thousand two hundred and thirty four volunteers aged below one and ninety years. P. falciparum parasitaemia rates and parasite density, splenomegaly, bednet use and chloroquine consumption. All subjects with P. falciparum positive smears were treated with chloroquine. The population prevalence of parasitaemia was 62.1% with the predominant species being P. falciparum (100%) and P. malariae in the minority (3.5%); P. ovale was not seen. The prevalence of parasitaemia in subjects older than 20 years and in those under ten years was 36% and 85%, respectively. The geometric mean parasite density started to decline by the age of six years. The splenomegaly rate in subjects over the age of 12 years and in those under nine years was 19.8% and 63.1%, respectively. Bednet use and chloroquine ...
Annals of Tropical Medicine And Parasitology, 2000
A cross-sectional study of pregnant women was conducted at Nsambya Hospital in Kampala, to invest... more A cross-sectional study of pregnant women was conducted at Nsambya Hospital in Kampala, to investigate the prevalence and effect of Plasmodium falciparum infections during pregnancy, in a peri-urban/urban location. Overall, 544 pregnant women were recruited when they presented at the labour ward for delivery. After giving informed consent, each subject answered a questionnaire and underwent a physical examination, and peripheral-blood samples were obtained. After each uncomplicated delivery, samples of placental and cord blood were obtained from the placenta and infant, respectively, and infant birthweights were recorded. Smears were prepared from the blood samples and checked for parasites. Only 46 and 36 of the 537 women investigated were positive for P. falciparum infection in their peripheral and placental blood, respectively. Plasmodium falciparum was the only parasite encountered. The prevalences of low birthweight and maternal parasitaemia and the intensities of maternal infection were each greater in primigravidae than secundi-or multi-gravidae. Despite the low prevalence of parasitaemia in this population, P. falciparum infection in the primigravidae was a signi® cant contributor to their ill health, leading to low birthweights in their infants.
SE36 antigen, derived from serine repeat antigen 5 (SERA5) of Plasmodium falciparum, is a promisi... more SE36 antigen, derived from serine repeat antigen 5 (SERA5) of Plasmodium falciparum, is a promising blood stage malaria vaccine candidate. Designated as BK-SE36, the SE36 antigen was formulated with aluminum hydroxyl gel (AHG) and produced under Good Manufacturing Practice (GMP) constraints. In a Phase Ib clinical trial and follow-up study in Uganda, the risk for malaria symptoms was reduced by 72% compared with the control group. Although promising, the number of responders to the vaccine in 6-20years-olds was approximately 30% with the majority in the younger cohort. This is in contrast to the phase Ia clinical trial where response to the vaccine was 100% in Japanese malaria naive adults. A consideration that can be of importance is the involvement of host genetic factors that may influence the ability to mount an effective immune response to vaccination as well as susceptibility to malaria infection. We, therefore, analyzed allelic polymorphism of human leukocyte antigen (HLA)-DRB1 alleles using sequence-based typing (SBT). In this study, DRB1 alleles did not influence antibody response to BK-SE36 and the vaccinees susceptibility to clinical malaria.
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Papers by Thomas Egwang