Bharat Jha

Genes on chromosomes 1 and 13 have significant effects on Ascaris infection

Nematode parasites show a characteristic aggregated distribution among hosts. This observation has important implications for pathogenesis, immunology, and control of these infections, but the relative roles of environment and genetics in determining these patterns have remained uncertain. This paper presents the results of the first genome scan for susceptibility to infection with roundworm (Ascaris lumbricoides). Data on 375 genetic markers were generated for each of 444 members of a genetically isolated Nepalese population, the Jirels. Ascaris worm burden as assessed by egg counts was measured in these same individuals by using the Kato Katz thick smear method. The extensive genealogical data available for the population allowed assignment of all 444 individuals to a single pedigree that contained 6,209 pairs of relatives that were informative for genetic analysis. A variance components linkage analysis resulted in the unequivocal localization of two genes (one on chromosome 1 and another on chromosome 13) with clear, significant effects on susceptibility to Ascaris infection. This is the first evidence that individual quantitative trait loci influence variation in Ascaris burden in humans.

Disentangling hybridization and host colonization in parasitic roundworms of humans and pigs

Knowledge of cross-transmission and hybridization between parasites of humans and reservoir hosts is critical for understanding the evolution of the parasite and for implementing control programmes. There is now a consensus that populations of pig and human Ascaris (roundworms) show significant genetic subdivision. However, it is unclear whether this has resulted from a single or multiple host shift(s). Furthermore, previous molecular data have not been sufficient to determine whether sympatric populations of human and pig Ascaris can exchange genes. To disentangle patterns of host colonization and hybridization, we used 23 microsatellite loci to conduct Bayesian clustering analyses of individual worms collected from pigs and humans. We observed strong differentiation between populations which was primarily driven by geography, with secondary differentiation resulting from host affiliation within locations. This pattern is consistent with multiple host colonization events. However, there is low support for the short internal branches of the dendrograms. In part, the relationships among clusters may result from current hybridization among sympatric human and pig roundworms. Indeed, congruence in three Bayesian methods indicated that 4 and 7% of roundworms sampled from Guatemala and China, respectively, were hybrids. These results indicate that there is contemporary cross-transmission between populations of human and pig Ascaris.

Localization of Multiple Quantitative Trait Loci Influencing Susceptibility to Infection with Ascaris lumbricoides

A linkage-based genome scan of 1,258 members of a single pedigree of the Jirel population of Nepal localized 6 potential quantitative trait loci (QTLs) influencing susceptibility to infection with Ascaris lumbricoides, the most common soil-transmitted intestinal helminth. Three QTLs exhibited genomewide significance, including QTLs on chromosomes 13 (logarithm of the odds ratio [LOD] score, 3.37; genomewide P = .013, 8 (LOD score, 3.03; genomewide P = .031), and 11 (LOD score, 3.19; genomewide P = .020). Another QTL on chromosome 1 approached significance (LOD score, 2.72; genomewide P = .067). There was suggestive evidence of linkage for 2 additional loci on chromosomes 1 and 13.

Landscape Genetics Reveals Focal Transmission of a Human Macroparasite

Macroparasite infections (e.g., helminths) remain a major human health concern. However, assessing transmission dynamics is problematic because the direct observation of macroparasite dispersal among hosts is not possible. We used a novel landscape genetics approach to examine transmission of the human roundworm Ascaris lumbricoides in a small human population in Jiri, Nepal. Unexpectedly, we found significant genetic structuring of parasites, indicating the presence of multiple transmission foci within a small sampling area (∼14 km2). We analyzed several epidemiological variables, and found that transmission is spatially autocorrelated around households and that transmission foci are stable over time despite extensive human movement. These results would not have been obtainable via a traditional epidemiological study based on worm counts alone. Our data refute the assumption that a single host population corresponds to a single parasite transmission unit, an assumption implicit in many classic models of macroparasite transmission. Newer models have shown that the metapopulation-like pattern observed in our data can adversely affect targeted control strategies aimed at community-wide impacts. Furthermore, the observed metapopulation structure and local mating patterns generate an excess of homozygotes that can accelerate the spread of recessive traits such as drug resistance. Our study illustrates how molecular analyses complement traditional epidemiological information in providing a better understanding of parasite transmission. Similar landscape genetic approaches in other macroparasite systems will be warranted if an accurate depiction of the transmission process is to be used to inform effective control strategies.

Two Quantitative Trait Loci Influence Whipworm (Trichuris trichiura) Infection in a Nepalese Population

BACKGROUND Whipworm (Trichuris trichiura) infection is a soil-transmitted helminth infection that affects >1 billion people. It is a serious public health problem in many developing countries and can result in deficits in growth and cognitive development. In a follow-up study of significant heritability for whipworm infection, we conducted the first genome scan for quantitative trait loci (QTL) influencing the heritability of susceptibility to this important parasitic disease. METHODS Whipworm egg counts were determined for 1,253 members of the Jirel population of eastern Nepal. All individuals in the study sample belonged to a single pedigree including >26,000 pairs of relatives that are informative for genetic analysis. RESULTS Linkage analysis of genome scan data generated for the pedigree provided unambiguous evidence for 2 QTL influencing susceptibility to whipworm infection, one located on chromosome 9 (logarithm of the odds ratio [LOD] score, 3.35; genomewide P = .0138) and the other located on chromosome 18 (LOD score, 3.29; genomewide P = .0159). There was also suggestive evidence that 2 loci located on chromosomes 12 and 13 influenced whipworm infection. CONCLUSION The results of this first genome scan for T. trichiura egg counts provides new information on the determinants of genetic predisposition to whipworm infection.

Genetic Influences on Plasma Cytokine Variation in a Parasitized Population

The soil-transmitted helminths are the most common helminthic infections, affecting about one-fourth of the worlds population. There is a significant genetic component to susceptibility to infection with these organisms. Substantial changes in plasma cytokine levels are associated with helminthic infections, and there may be significant genetic components to this cytokine variation. Six plasma cytokine levels were assessed for 367 members of a single pedigree from the Jirel population of eastern Nepal. This population experiences moderate rates of infection with geohelminths. Sex, age, helminthic infection, infection with Giardia, and presence of a household latrine were considered as covariates in all analyses of the cytokine data. The analyses of the single Jirel pedigree revealed significant heritabilities for IFN-;gg (h2-0.654_0.096), TNF-;ga (h2-0.458_0.101), IL-2 (h2-0.583_0.101), IL-4 (h2-0.700_0.095), IL-5 (h2-0.676_0.087), and IL-10 (h2-0.597_0.093). The ratios of IL-4 to IFN-;gg and of IL-10 to IFN-;gg were used as indicators of the degree of type 2 bias in immunological response; analyses of these variables indicated that approximately 40-60% of the variation (h2-0.400-0.577) in these derived measures of relative type 2/type 1 response is due to genetic factors.

Re-emergence of susceptibility to conventional first line drugs in Salmonella isolates from enteric fever patients in Nepal

INTRODUCTION Enteric fever is endemic in Nepal and poses a significant public health burden. The first-line drugs ampicillin, chloramphenicol, and cotrimoxazole have not been part of empirical therapy for two decades due to the development of multidrug-resistant Salmonella strains. The objective of this study was to determine the antibiogram pattern of Salmonella serovars isolated from the blood of clinically suspected enteric fever patients. METHODOLOGY A cross sectional study was carried out in a tertiary care hospital in Lalitpur, Nepal, between July 2011 and February 2012. Standard microbiological procedures were followed during collection and processing of blood samples, isolation and identification of Salmonella serotypes. The antimicrobial sensitivity of ampicillin, chloramphenicol, cotrimoxazole, nalidixic acid, and ciprofloxacin was determined using a modified Kirby-Bauer disk diffusion method as per the guidelines of the Clinical and Laboratory Standards Institute. RESULTS Out of 86 Salmonella isolates, 56 (65.1%) were Salmonella Typhi and 30 (34.9%) were Salmonella Paratyphi A. Salmonella Typhi were 100% sensitive to chloramphenicol, cotrimoxazole, and ciprofloxacin and 98.2% sensitive to ampicillin. Similarly, Salmonella Paratyphi A isolates were 100% sensitive to ampicillin and cotrimoxazole and 96.7% sensitive to chloramphenicol and ciprofloxacin. More than 90.0% of isolates were nalidixic acid resistant and none of the Salmonella isolates were multi-drug resistant. CONCLUSIONS This study revealed the increasing frequency of nalidixic acid-resistant Salmonella isolates, indicating the possibility of fluoroquinolone resistance in near future. Furthermore, re-emergence of susceptibility to conventional first-line drugs ampicillin, chloramphenicol, and cotrimoxazole supports the possibility of using these drugs in empirical therapy.

Evaluation of Qualitative Methods for Phenotyping Brachymesophalangia - V from Radiographs of Children

Objective: Brachymesophalangia‐V (BMP‐V), the general term for a short and broad middle phalanx of the 5th digit, presents both alone and in a large number of complex brachydactylies and developmental disorders. Past anthropological and epidemiological studies of growth and development have examined the prevalence of BMP‐V because small developmental disorders may signal more complex disruptions of skeletal growth and development. Historically, however, consensus on qualitative phenotype methodology has not been established. In large‐scale, non‐clinical studies such as the Fels Longitudinal Study and the Jiri Growth Study, quantitative assessment of the hand is not always the most efficient manner of screening for skeletal dysmorphologies. The current study evaluates qualitative phenotyping techniques for BMP‐V used in past anthropological studies of growth and development to establish a useful and reliable screening method for large study samples.

Serum uric acid level in newly diagnosed essential hypertension in a Nepalese population: A hospital based cross sectional study

OBJECTIVE To develop the missing link between hyperuricemia and hypertension. METHODS The study was conducted in Department of Biochemistry in collaboration with Nephrology Unit of Internal Medicine Department. Hypertension was defined according to blood pressure readings by definitions of the Seventh Report of the Joint National Committee. Totally 205 newly diagnosed and untreated essential hypertensive cases and age-sex matched normotensive controls were enrolled in the study. The potential confounding factors of hyperuricemia and hypertension in both cases and controls were controlled. Uric acid levels in all participants were analyzed. RESULTS Renal function between newly diagnosed hypertensive cases and normotensive healthy controls were adjusted. The mean serum uric acid observed in newly diagnosed hypertensive cases and in normotensive healthy controls were (290.05±87.05) μmol/L and (245.24±99.38) μmol/L respectively. A total of 59 (28.8%) participants of cases and 28 (13.7%) participants of controls had hyperuricemia (odds ratio 2.555 (95% CI: 1.549-4.213), P<0.001). CONCLUSIONS The mean serum uric acid levels and number of hyperuricemic subjects were found to be significantly higher in cases when compared to controls.

Heritability of brachydactyly type A3 in children, adolescents, and young adults from an endogamous population in eastern Nepal.

ABSTRACT Brachymesophalangia-V (BMP-V), a short and broad middle phalanx of the fifth digit, is the most common of all skeletal anomalies of the hand. When this feature appears alone, it is clinically known as brachydactyly type A3 (BDA3). A high prevalence of BDA3 has been observed among the children of the Jirel ethnic group in eastern Nepal. As part of the Jiri Growth Study, a hand-wrist radiograph is taken annually of each child to assess skeletal development. For this study the most recent radiographs of 1,357 Jirel children, adolescents, and young adults (676 boys, 681 girls), age 3–20 years, were examined for the presence or absence of BDA3, to report the prevalence and estimate the heritability of BDA3 in the Jirel population. The overall prevalence of BDA3 in this sample was 10.5% (12.9% of the males and 8.9% of the females were classified as BDA3 affected). The additive genetic heritability of BDA3 was statistically significant in this sample (h2 ± SE = 0.87 ± 0.16, p < 0.0001). This study is the first to estimate the prevalence and heritability of BDA3 in a large South Asian family-based sample.