A measles IgM rapid diagnostic test to address challenges with national measles surveillance and response in Malaysia.

INTRODUCTION: A lateral flow rapid diagnostic test (RDT) enables detection of measles specific immunoglobulin M (IgM) antibody in serum, capillary blood, and oral fluid with accuracy consistent with enzyme immunoassay (EIA). The objectives of the study were: 1) to assess measles RDT inter-reader agreement between two clinic staff; 2) to assess the sensitivity and specificity of the measles RDT relative to standard surveillance testing in a low transmission setting; 3) to evaluate the knowledge, attitudes, and practices of staff in clinics using the RDT; and 4) to assess the impact of RDT testing on the measles public health response in Malaysia. MATERIALS AND METHODS: The clinic-based prospective evaluation included all suspected measles cases captured by routine measles surveillance at 34 purposely selected clinics in 15 health districts in Malaysia between September 2019 and June 2020, following day-long regional trainings on RDT use. Following informed consent, four specimens were collected from each suspected case, including those routinely collected for standard surveillance [serum for EIA and throat swabs for quantitative reverse transcriptase polymerase chain reaction (RT-qPCR)] together with capillary blood and oral fluid tested with RDTs during the study. RDT impact was evaluated by comparing the rapidity of measles public health response between the pre-RDT implementation (December 2018 to August 2019) and RDT implementation periods (September 2019 to June 2020). To assess knowledge, attitudes, and practices of RDT use, staff involved in the public health management of measles at the selected sites were surveyed. RESULTS: Among the 436 suspect cases, agreement of direct visual readings of measles RDT devices between two health clinic staff was 99% for capillary blood (k = 0.94) and 97% for oral fluid (k = 0.90) specimens. Of the total, 45 (10%) were positive by measles IgM EIA (n = 44, including five also positive by RT-qPCR) or RT-qPCR only (n = 1), and 38 were positive by RDT (using either capillary blood or oral fluid). Using measles IgM EIA or RT-qPCR as reference, RDT sensitivity using capillary blood was 43% (95% CI: 30%-58%) and specificity was 98% (95% CI: 96%-99%); using oral fluid, sensitivity (26%, 95% CI: 15%-40%) and specificity (97%, 95% CI: 94%-98%) were lower. Nine months after training, RDT knowledge was high among staff involved with the public health management of measles (average quiz score of 80%) and was highest among those who received formal training (88%), followed by those trained during supervisory visits (83%). During the RDT implementation period, the number of days from case confirmation until initiation of public response decreased by about 5 days. CONCLUSION: The measles IgM RDT shows >95% inter-reader agreement, high retention of RDT knowledge, and a more rapid public health response. However, despite ≥95% RDT specificity using capillary blood or oral fluid, RDT sensitivity was <45%. Higher-powered studies using highly specific IgM assays and systematic RT-qPCR for case confirmation are needed to establish the role of RDT in measles elimination settings.

Lessons learned from the implementation of integrated serosurveillance of communicable diseases in the Americas / Enseñanzas obtenidas en la aplicación de la serovigilancia integrada de las enfermedades transmisibles en la Región de las Américas / Lições aprendidas com a implementação da vigilância sorológica integrada de doenças transmissíveis nas Américas

ABSTRACT Objective. Systematize the experience and identify challenges and lessons learned in the implementation of an initiative for integrated serosurveillance of communicable diseases using a multiplex bead assay in countries of the Americas. Methods. Documents produced in the initiative were compiled and reviewed. These included concept notes, internal working papers, regional meetings reports, and survey protocols from the three participating countries (Mexico, Paraguay, and Brazil) and two additional countries (Guyana and Guatemala) where serology for several communicable diseases was included in neglected tropical diseases surveys. Information was extracted and summarized to describe the experience and the most relevant challenges and lessons learned. Results. Implementing integrated serosurveys requires interprogrammatic and interdisciplinary work teams for the design of survey protocols to respond to key programmatic questions aligned to the needs of the countries. Valid laboratory results are critical and rely on the standardized installment and roll-out of laboratory techniques. Field teams require adequate training and supervision to properly implement survey procedures. The analysis and interpretation of serosurveys results should be antigen-specific, contextualizing the responses for each disease, and triangulated with programmatic and epidemiological data for making decisions tailored to specific population socioeconomic and ecologic contexts. Conclusions. Integrated serosurveillance as a complementary tool for functional epidemiological surveillance systems is feasible to use and key components should be considered: political engagement, technical engagement, and integrated planning. Aspects such as designing the protocol, selecting target populations and diseases, laboratory capacities, anticipating the capacities to analyze and interpret complex data, and how to use it are key.

Resumen Objetivo. Sistematizar la experiencia y determinar los desafíos y las enseñanzas obtenidas durante la aplicación de una iniciativa de serovigilancia integrada de enfermedades transmisibles mediante un ensayo de perlas múltiples en países de la Región de las Américas. Métodos. Se recopilaron y revisaron los documentos generados en el marco de la iniciativa. Estos incluían notas conceptuales, documentos de trabajo internos, informes de reuniones regionales y protocolos de encuesta de los tres países participantes (Brasil, México y Paraguay) y otros dos países (Guatemala y Guyana) donde en las encuestas sobre enfermedades tropicales desatendidas también se incluía la serología para varias enfermedades transmisibles. Se recabó y resumió la información para describir tanto la experiencia como los desafíos y las enseñanzas de mayor relevancia. Resultados. La realización de encuestas serológicas integradas requiere equipos de trabajo interprogramáticos e interdisciplinarios para la elaboración de protocolos de encuesta que permitan responder a cuestiones programáticas fundamentales y ajustadas a las necesidades de los países. Es imprescindible contar con resultados de laboratorio válidos, para lo que es preciso que sus técnicas e instalaciones estén estandarizadas. Para que los equipos de campo puedan ejecutar correctamente los procedimientos de la encuesta, deben contar con una formación y supervisión adecuadas. El análisis y la interpretación de los resultados de las encuestas serológicas deben ser específicos para cada antígeno, situar las respuestas en el contexto de cada enfermedad y triangularse con los datos programáticos y epidemiológicos para tomar decisiones adaptadas a los contextos socioeconómicos y ecológicos específicos de la población. Conclusiones. Es uso de la vigilancia serológica integrada como una herramienta complementaria en los sistemas funcionales de vigilancia epidemiológica es algo posible; para esto deben tenerse en cuenta ciertos elementos fundamentales: el compromiso político, el compromiso técnico y la planificación integrada. A tal efecto, son fundamentales ciertos elementos como el diseño del protocolo, la selección de los grupos poblacionales y las enfermedades objetivo, la capacidad de los laboratorios, y la previsión de las capacidades de análisis e interpretación de datos complejos y la forma de utilizarlos.

RESUMO Objetivo. Sistematizar a experiência e identificar desafios e lições aprendidas na implementação de uma iniciativa de vigilância sorológica integrada de doenças transmissíveis, usando ensaio de micro-esferas multiplex em países das Américas. Métodos. Os documentos produzidos na iniciativa foram compilados e examinados, e incluíram notas conceituais, documentos internos de trabalho, relatórios de reuniões regionais e protocolos de pesquisa dos três países participantes (México, Paraguai e Brasil) e de dois países adicionais (Guiana e Guatemala), onde a vigilância sorológica de várias doenças transmissíveis foi incluída em pesquisas sobre doenças tropicais negligenciadas. As informações foram extraídas e resumidas para descrever a experiência e os desafios e as lições aprendidas mais relevantes. Resultados. A implementação de inquéritos sorológicos integrados requer equipes de trabalho interprogramáticas e interdisciplinares para o delineamento de protocolos que respondam a questões programáticas chave, alinhadas com as necessidades dos países. Resultados laboratoriais válidos são essenciais, e dependem da instalação e implantação padronizadas de técnicas laboratoriais. As equipes de campo precisam de treinamento e supervisão apropriados para implementar adequadamente os procedimentos de pesquisa. A análise e a interpretação dos resultados dos inquéritos sorológicos devem ser antígeno-específicas, contextualizando as respostas para cada doença, e trianguladas com dados programáticos e epidemiológicos para a tomada de decisões adaptadas aos contextos socioeconômicos e ecológicos específicos de cada população. Conclusões. A vigilância sorológica integrada como ferramenta complementar para sistemas de vigilância epidemiológica funcionais é viável. Os componentes-chave a seguir devem ser considerados: engajamento político, engajamento técnico e planejamento integrado. Aspectos como o delineamento do protocolo, a seleção de populações-alvo e doenças-alvo, a capacidade laboratorial, a previsão das capacidades para análise e interpretação de dados complexos e como usá-los são fundamentais.

Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo.

The Democratic Republic of the Congo (DRC) has a high measles incidence despite elimination efforts and has yet to introduce rubella vaccine. We evaluated the performance of a prototype rapid digital microfluidics powered (DMF) enzyme-linked immunoassay (ELISA) assessing measles and rubella infection, by testing for immunoglobulin M (IgM), and immunity from natural infection or vaccine, by testing immunoglobulin G (IgG), in outbreak settings. Field evaluations were conducted during September 2017, in Kinshasa province, DRC. Blood specimens were collected during an outbreak investigation of suspected measles cases and tested for measles and rubella IgM and IgG using the DMF-ELISA in the field. Simultaneously, a household serosurvey for measles and rubella IgG was conducted in a recently confirmed measles outbreak area. DMF-ELISA results were compared with reference ELISA results tested at DRC's National Public Health Laboratory and the US Centers for Disease Control and Prevention. Of 157 suspected measles cases, rubella IgM was detected in 54% while measles IgM was detected in 13%. Measles IgG-positive cases were higher among vaccinated persons (87%) than unvaccinated persons (72%). In the recent measles outbreak area, measles IgG seroprevalence was 93% overall, while rubella seroprevalence was lower for children (77%) than women (98%). Compared with reference ELISA, DMF-ELISA sensitivity and specificity were 82% and 78% for measles IgG; 88% and 89% for measles IgM; 85% and 85% for rubella IgG; and 81% and 83% for rubella IgM, respectively. Rubella infection was detected in more than half of persons meeting the suspected measles case definition during a presumed measles outbreak, suggesting substantial unrecognized rubella incidence, and highlighting the need for rubella vaccine introduction into the national schedule. The performance of the DMF-ELISA suggested that this technology can be used to develop rapid diagnostic tests for measles and rubella.

Anthrax toxin receptor 2-dependent lethal toxin killing in vivo.

Anthrax toxin receptors 1 and 2 (ANTXR1 and ANTXR2) have a related integrin-like inserted (I) domain which interacts with a metal cation that is coordinated by residue D683 of the protective antigen (PA) subunit of anthrax toxin. The receptor-bound metal ion and PA residue D683 are critical for ANTXR1-PA binding. Since PA can bind to ANTXR2 with reduced affinity in the absence of metal ions, we reasoned that D683 mutant forms of PA might specifically interact with ANTXR2. We show here that this is the case. The differential ability of ANTXR1 and ANTXR2 to bind D683 mutant PA proteins was mapped to nonconserved receptor residues at the binding interface with PA domain 2. Moreover, a D683K mutant form of PA that bound specifically to human and rat ANTXR2 mediated killing of rats by anthrax lethal toxin, providing strong evidence for the physiological importance of ANTXR2 in anthrax disease pathogenesis.

Receptor-specific requirements for anthrax toxin delivery into cells.

The three proteins that constitute anthrax toxin self-assemble into toxic complexes after one of these proteins, protective antigen (PA), binds to tumor endothelial marker 8 (TEM8) or capillary morphogenesis protein 2 (CMG2) cellular receptors. The toxin receptor complexes are internalized, and acidic endosomal pH triggers pore formation by PA and translocation of the catalytic subunits into the cytosol. In this study we show that the pH threshold for conversion of the PA prepore to the pore and for translocation differs by approximately a pH unit, depending on whether the TEM8 or CMG2 receptor is used. For TEM8-associated toxin, these events can occur at close to neutral pH values, and they show relatively low sensitivity to ammonium chloride treatment in cells. In contrast, with CMG2-associated toxin, these events require more acidic conditions and are highly sensitive to ammonium chloride. We show, furthermore, that PA dissociates from TEM8 and CMG2 upon pore formation. Our results are consistent with a model in which translocation depends on pore formation and pore formation, in turn, depends on release of PA from its receptor. We propose that because PA binds to CMG2 with much higher affinity than it does to TEM8, a lower pH is needed to attenuate CMG2 binding to allow pore formation. Our results suggest that toxin can form pores at different points in the endocytic pathway, depending on which receptor is used for entry.

A soluble receptor decoy protects rats against anthrax lethal toxin challenge.

Successful postexposure treatment for inhalation anthrax is thought to include neutralization of anthrax toxin. The soluble anthrax toxin receptor/tumor endothelial marker 8 and capillary morphogenesis protein 2 (sATR/TEM8 and sCMG2, respectively) receptor decoys bind to anthrax toxin protective antigen (PA) and compete with cellular receptors for binding. Here, we show that, in a tissue-culture model of intoxication, sCMG2 is a 11.4-fold more potent antitoxin than sATR/TEM8 and that this increased activity corresponds to an approximately 1000-fold higher PA-binding affinity. Stoichiometric concentrations of sCMG2 protect rats against lethal toxin challenge, making sCMG2 one of the most effective anthrax antitoxins described to date.

Interactions between anthrax toxin receptors and protective antigen.

Since the anthrax mail attacks of 2001, much has been learned about the interactions between anthrax toxin and its receptors. Two distinct cellular receptors for anthrax toxin have been identified and are designated capillary morphogenesis protein 2 (CMG2) and anthrax toxin receptor/tumor endothelial marker 8 (ATR/TEM8). The molecular details of the toxin-receptor interactions have been revealed through crystallographic, biochemical and genetic studies. In addition, a novel pathway by which anthrax toxin enters cells is starting to be uncovered.

Crystal structure of the von Willebrand factor A domain of human capillary morphogenesis protein 2: an anthrax toxin receptor.

Anthrax toxin is released from Bacillus anthracis as three monomeric proteins, which assemble into toxic complexes at the surface of receptor-bearing host cells. One of the proteins, protective antigen (PA), binds to receptors and orchestrates the delivery of the other two (the lethal and edema factors) into the cytosol. PA has been shown to bind to two cellular receptors: anthrax toxin receptor/tumor endothelial marker 8 and capillary morphogenesis protein 2 (CMG2). Both are type 1 membrane proteins that include an approximately 200-aa extracellular von Willebrand factor A (VWA) domain with a metal ion-dependent adhesion site (MIDAS) motif. The anthrax toxin receptor/tumor endothelial marker 8 and CMG2 VWA domains share approximately 60% amino acid identity and bind PA directly in a metal-dependent manner. Here, we report the crystal structure of the CMG2 VWA domain, with and without its intramolecular disulfide bond, to 1.5 and 1.8 A, respectively. Both structures contain a carboxylate ligand-mimetic bound at the MIDAS and appear as open conformations when compared with the VWA domains from alpha-integrins. The CMG2 structures provide a template to begin probing the high-affinity CMG2-PA interaction (200 pM) and may facilitate understanding of toxin assembly/internalization and the development of new anthrax treatments. The structural data also allow molecular interpretation of known CMG2 VWA domain mutations linked to the genetic disorders, juvenile hyaline fibromatosis, and infantile systemic hyalinosis.

Human capillary morphogenesis protein 2 functions as an anthrax toxin receptor.

Bacillus anthracis secretes two bipartite toxins thought to be involved in anthrax pathogenesis and resulting death of the host. The current model for intoxication is that protective antigen (PA) toxin subunits bind a single group of cell-surface anthrax toxin receptors (ATRs), encoded by the tumor endothelial marker 8 (TEM8) gene. The ATR/TEM8-PA interaction is mediated by the receptor's extracellular domain related to von Willebrand factor type A or integrin inserted domains (VWA/I domains). A metal ion-dependent adhesion site (MIDAS) located within this domain of the ATR/TEM8 protein chelates a divalent cation critical for PA binding. In this report, we identify a second PA receptor encoded by capillary morphogenesis gene 2 (CMG2), which has 60% amino acid identity to ATR/TEM8 within the VWA/I domain, as well as a conserved MIDAS motif. A recombinant CMG2 protein bound PA and mediated toxin internalization when expressed on receptor-deficient cells. Binding between the CMG2 VWA/I domain and PA was shown to be direct and metal-dependent, although the cation specificity of this interaction is different than that observed with ATR/TEM8. Northern blot analysis revealed that CMG2 is widely expressed in human tissues, indicating that this receptor is likely to be relevant for disease pathogenesis. Finally, a soluble version of the CMG2 VWA/I domain inhibited intoxication of cells expressing endogenous toxin receptors when it was added to PA at a 3:1 ratio. These studies distinguish CMG2 as a second anthrax toxin receptor and identify a potent antitoxin that may prove useful for the treatment of anthrax.

Nucleic acid-independent retrovirus assembly can be driven by dimerization.

The Gag protein of retroviruses alone can polymerize into regular virus-like particles (VLPs) both in vitro and in vivo. In most circumstances the capsid (CA) and nucleocapsid (NC) domains of Gag as well as some form of nucleic acid are required for this process. The mechanism by which NC-nucleic acid interaction promotes assembly has remained obscure. We show here that while deletion of the NC domain of Rous sarcoma virus Gag abolishes formation and budding of VLPs at the plasma membranes of baculovirus-infected insect cells, replacement of NC with a dimer-forming leucine zipper domain restores budding of spherical particles morphologically similar to wild-type VLPs. The positioning of the dimerization domain appears to be critical for proper assembly, as the insertion of a 5-amino-acid flexible linker upstream of the zipper domain leads to budding of tubular rather than spherical particles. Similar tubular particles are formed when the same linker is inserted upstream of NC. The tubes are morphologically distinct from tubes formed when the p10 domain upstream of CA is deleted. The fact that a foreign dimerization domain can functionally mimic NC suggests that the role of nucleic acid in retroviral assembly is not to serve as a scaffold but rather to promote the formation of Gag dimers, which are critical intermediates in the polymerization of the Gag shell.