Category: Publications

Srikiatkhachorn A, Wichit S, Gibbons RV, Green S, Libraty DH, Endy TP, Ennis FA, Kalayanarooj S, Rothman AL

PLoS ONE 2012;7(12):e51335

PMID: 23284680

Abstract

BACKGROUND: Infection with dengue viruses (DENV) causes a wide range of manifestations from asymptomatic infection to a febrile illness called dengue fever (DF), to dengue hemorrhagic fever (DHF). The in vivo targets of DENV and the relation between the viral burden in these cells and disease severity are not known.

METHOD: The levels of positive and negative strand viral RNA in peripheral blood monocytes, T/NK cells, and B cells and in plasma of DF and DHF cases were measured by quantitative RT-PCR.

RESULTS: Positive strand viral RNA was detected in monocytes, T/NK cells and B cells with the highest amounts found in B cells. Viral RNA levels in CD14+ cells and plasma were significantly higher in DHF compared to DF, and in cases with a secondary infection compared to those undergoing a primary infection. The distribution of viral RNA among cell subpopulations was similar in DF and DHF cases. Small amounts of negative strand RNA were found in a few cases only. The severity of plasma leakage correlated with viral RNA levels in plasma and in CD14+ cells.

CONCLUSIONS: B cells were the principal cells containing DENV RNA in peripheral blood, but overall there was little active DENV RNA replication detectable in peripheral blood mononuclear cells (PBMC). Secondary infection and DHF were associated with higher viral burden in PBMC populations, especially CD14+ monocytes, suggesting that viral infection of these cells may be involved in disease pathogenesis.

Friberg H, Jaiswal S, West K, O’Ketch M, Rothman AL, Mathew A

Viral Immunol. 2012 Oct;25(5):348-59

PMID: 22934599

Abstract

Dengue, caused by the four serotypes of dengue virus (DENV), represents an expanding global health challenge. The potential for serotype-cross-reactive antibodies to exacerbate disease during a secondary infection with a heterologous DENV serotype has driven efforts to study human DENV-specific antibodies. Most DENV-specific antibodies generated in humans are serotype-cross-reactive, weakly neutralizing, and directed against the immature pre-membrane (prM), envelope (E), and nonstructural 1 (NS1) proteins. To broaden the characterization of human DENV-specific antibodies, we assessed B-cell responses by ELISpot assays and isolated B cells from the peripheral blood of a human subject with previous DENV infection. Forty-eight human IgG monoclonal antibodies (hMAbs) were initially characterized by their potential to bind to an inactivated lysate of DENV-infected cells. Subsequently, most DENV-specific hMAbs were found to bind soluble, recombinant E protein (rE). Two hMAbs were unable to bind rE, despite strongly binding to the DENV-infected cell lysate. Further analyses showed that these two hMAbs bound conformation-dependent, reduction-sensitive epitopes on E protein. These data shed light on the breadth of DENV-specific hMAbs generated within a single immune donor.

Aldstadt J, Yoon IK, Tannitisupawong D, Jarman RG, Thomas SJ, Gibbons RV, Uppapong A, Iamsirithaworn S, Rothman AL, Scott TW, Endy T

Trop. Med. Int. Health 2012 Sep;17(9):1076-85

PMID: 22808917

Abstract

OBJECTIVE: To determine the temporal intervals at which spatial clustering of dengue hospitalisations occurs.

METHODS: Space-time analysis of 262 people hospitalised and serologically confirmed with dengue virus infections in Kamphaeng Phet, Thailand was performed. The cases were observed between 1 January 2009 and 6 May 2011. Spatial coordinates of each patient’s home were captured using the Global Positioning System. A novel method based on the Knox test was used to determine the temporal intervals between cases at which spatial clustering occurred. These intervals are indicative of the length of time between successive illnesses in the chain of dengue virus transmission.

RESULTS: The strongest spatial clustering occurred at the 15-17-day interval. There was also significant spatial clustering over short intervals (2-5 days). The highest excess risk was observed within 200 m of a previous hospitalised case and significantly elevated risk persisted within this distance for 32-34 days.

CONCLUSIONS: Fifteen to seventeen days are the most likely serial interval between successive dengue illnesses. This novel method relies only on passively detected, hospitalised case data with household locations and provides a useful tool for understanding region-specific and outbreak-specific dengue virus transmission dynamics.

Yoon IK, Getis A, Aldstadt J, Rothman AL, Tannitisupawong D, Koenraadt CJ, Fansiri T, Jones JW, Morrison AC, Jarman RG, Nisalak A, Mammen MP, Thammapalo S, Srikiatkhachorn A, Green S, Libraty DH, Gibbons RV, Endy T, Pimgate C, Scott TW

PLoS Negl Trop Dis 2012;6(7):e1730

PMID: 22816001

Abstract

BACKGROUND: Based on spatiotemporal clustering of human dengue virus (DENV) infections, transmission is thought to occur at fine spatiotemporal scales by horizontal transfer of virus between humans and mosquito vectors. To define the dimensions of local transmission and quantify the factors that support it, we examined relationships between infected humans and Aedes aegypti in Thai villages.

METHODOLOGY/PRINCIPAL FINDINGS: Geographic cluster investigations of 100-meter radius were conducted around DENV-positive and DENV-negative febrile “index” cases (positive and negative clusters, respectively) from a longitudinal cohort study in rural Thailand. Child contacts and Ae. aegypti from cluster houses were assessed for DENV infection. Spatiotemporal, demographic, and entomological parameters were evaluated. In positive clusters, the DENV infection rate among child contacts was 35.3% in index houses, 29.9% in houses within 20 meters, and decreased with distance from the index house to 6.2% in houses 80-100 meters away (p<0.001). Significantly more Ae. aegypti were DENV-infectious (i.e., DENV-positive in head/thorax) in positive clusters (23/1755; 1.3%) than negative clusters (1/1548; 0.1%). In positive clusters, 8.2% of mosquitoes were DENV-infectious in index houses, 4.2% in other houses with DENV-infected children, and 0.4% in houses without infected children (p<0.001). The DENV infection rate in contacts was 47.4% in houses with infectious mosquitoes, 28.7% in other houses in the same cluster, and 10.8% in positive clusters without infectious mosquitoes (p<0.001). Ae. aegypti pupae and adult females were more numerous only in houses containing infectious mosquitoes.

CONCLUSIONS/SIGNIFICANCE: Human and mosquito infections are positively associated at the level of individual houses and neighboring residences. Certain houses with high transmission risk contribute disproportionately to DENV spread to neighboring houses. Small groups of houses with elevated transmission risk are consistent with over-dispersion of transmission (i.e., at a given point in time, people/mosquitoes from a small portion of houses are responsible for the majority of transmission).

Yoon IK, Rothman AL, Tannitisupawong D, Srikiatkhachorn A, Jarman RG, Aldstadt J, Nisalak A, Mammen MP, Thammapalo S, Green S, Libraty DH, Gibbons RV, Getis A, Endy T, Jones JW, Koenraadt CJ, Morrison AC, Fansiri T, Pimgate C, Scott TW

J. Infect. Dis. 2012 Aug;206(3):389-98

PMID: 22615312

Abstract

BACKGROUND: The understanding of dengue virus (DENV) transmission dynamics and the clinical spectrum of infection are critical to informing surveillance and control measures. Geographic cluster studies can elucidate these features in greater detail than cohort studies alone.

METHODS: A 4-year longitudinal cohort and geographic cluster study was undertaken in rural Thailand. Cohort children underwent pre-/postseason serology and active school absence-based surveillance to detect inapparent and symptomatic dengue. Cluster investigations were triggered by cohort dengue and non-dengue febrile illnesses (positive and negative clusters, respectively).

RESULTS: The annual cohort incidence of symptomatic dengue ranged from 1.3% to 4.4%. DENV-4 predominated in the first 2 years, DENV-1 in the second 2 years. The inapparent-to-symptomatic infection ratio ranged from 1.1:1 to 2.9:1. Positive clusters had a 16.0% infection rate, negative clusters 1.1%. Of 119 infections in positive clusters, 59.7% were febrile, 20.2% were afebrile with other symptoms, and 20.2% were asymptomatic. Of 16 febrile children detected during cluster investigations who continued to attend school, 9 had detectable viremia.

CONCLUSIONS: Dengue transmission risk was high near viremic children in both high- and low-incidence years. Inapparent infections in the cohort overestimated the rate of asymptomatic infections. Ambulatory children with mild febrile viremic infections could represent an important component of dengue transmission.