PLoS Neglected Tropical Diseases: New Articles

The Costs of Preventing and Treating Chagas Disease in Colombia

2008-11-18T08:00:00Z

by Marianela Castillo-Riquelme, Felipe Guhl, Brenda Turriago, Nestor Pinto, Fernando Rosas, Mónica Flórez Martínez, Julia Fox-Rushby, Clive Davies, Diarmid Campbell-Lendrum

Author Summary

Chagas disease is one of the most important vector-transmitted diseases in Latin America. Many patients with Chagas go undiagnosed for years, and because symptoms of the chronic condition are similar to those of other cardiac conditions, the burden of the disease is not evident. This leads to underestimation of the burden that Chagas disease places on healthcare resources, which in many cases translates into inadequate prioritisation for prevention. This study assessed the cost of Chagas disease in Colombia in comparison to the cost of prevention. Measuring the cost of treatment for Chagas disease is challenging. In this study we used a method that combines retrospective review of costs for prevention activities and for treatment of chronic Chagas disease patients, and we estimated utilisation of services using experts' consensus. We found that the cost of treating Chagas disease is substantial, even though many people are not receiving appropriate care. On the other hand, we show that preventing Chagas disease transmission through insecticide spraying activities is affordable in Colombia and therefore should be conducted more systematically. This study provides the basic inputs to conduct a full economic evaluation of Chagas disease prevention.

Quantitative Detection of Schistosoma japonicum Cercariae in Water by Real-Time PCR

2008-11-18T08:00:00Z

by Yuen Wai Hung, Justin Remais

Author Summary

Schistosomiasis ranks second only to malaria among parasitic diseases with regard to the number of people infected and those at risk. Schistosoma japonicum is the species that causes human and animal disease in China, the Philippines, and to a lesser extent, Indonesia. Recent evidence of schistosomiasis re-emergence in China has reinforced the need for active disease surveillance in these areas. Schistosomiasis infection occurs through contact with water contaminated with S. japonicum cercariae, the free-living stage of the parasite shed from intermediate host snails. Current practice of detecting cercariae in the environment uses sentinel mice, a method with serious limitations in which mice are exposed to environmental water and then maintained for 6 weeks before being dissected to count worms. The method is labor intensive and costly in terms of time and resources, making it logistically prohibitive to monitor water contact sites regularly or comprehensively. Here we develop a quantitative PCR assay to measure S. japonicum cercariae concentration in water, providing a potential method for rapid and reliable data collection in the field, potentially replacing the use of live animal models.

Warmer Weather Linked to Tick Attack and Emergence of Severe Rickettsioses

2008-11-18T08:00:00Z

by Philippe Parola, Cristina Socolovschi, Luc Jeanjean, Idir Bitam, Pierre-Edouard Fournier, Albert Sotto, Pierre Labauge, Didier Raoult

Author Summary

The impact of climate on the behaviour of the worldwide dog tick Rhipicephalus sanguineus is a cause of concern. This tick is a vector for life-threatening organisms including Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, R. conorii, the agent of Mediterranean spotted fever, and the ubiquitous emerging pathogen R. massiliae. A focus of spotted fever was investigated in France in May 2007. One patient was found to be infected by R. conorii, whereas the other was infected by R. massiliae. Theses cases were original because of ophthalmic involvements, and the report of the second case of R. massiliae infection in the scientific literature. During an entomological survey, dense populations of Rh. sanguineus were found in the house where the patient had been bitten by ticks. Ticks were infected with either R. conorii or R. massiliae. Interestingly, April 2007 was the warmest since 1950, with summer-like temperatures. In this work, we show that the human affinity of Rh. sanguineus is increased in warmer temperatures, and provide evidence that this cluster of cases was related to a warming-mediated increase in the aggressiveness of Rh. sanguineus, leading to increased human attacks. From a global perspective, we predict that as a result of globalisation and warming, more pathogens transmitted by the brown dog tick may emerge in the future.

Controlled Chaos of Polymorphic Mucins in a Metazoan Parasite (Schistosoma mansoni) Interacting with Its Invertebrate Host (Biomphalaria glabrata)

2008-11-11T08:00:00Z

by Emmanuel Roger, Christoph Grunau, Raymond J. Pierce, Hirohisa Hirai, Benjamin Gourbal, Richard Galinier, Rémi Emans, Italo M. Cesari, Céline Cosseau, Guillaume Mitta

Author Summary

Contrary to the traditional view that immunity in invertebrates is limited to non-specific mechanisms, recent studies have shown that they have diverse, specific immune receptors. An example is provided by the FREPs of the mollusk Biomphalaria glabrata, polymorphic members of the immunoglobulin superfamily. This capacity for an individual or population-based polymorphic immune response raises the question of whether a corresponding polymorphism exists in parasites of invertebrates, as would be expected in an “arms race” between host and parasite. We have indeed identified such polymorphic molecules in Schistosoma mansoni, a flatworm parasite of B. glabrata, by comparing two strains of schistosome that are respectively compatible and incompatible with the same mollusk host strain. However, in contrast to antigenic variation in protozoan parasites that is based on an extensive gene repertoire, we show here that a high level of polymorphism in these S. mansoni polymorphic mucins (SmPoMucs) is generated from a low number of genes by a complex cascade of mechanisms, a “controlled chaos”.

Correlative and Dynamic Imaging of the Hatching Biology of Schistosoma japonicum from Eggs Prepared by High Pressure Freezing

2008-11-11T08:00:00Z

by Malcolm K. Jones, Sze How Bong, Kathryn M. Green, Philadelphia Holmes, Mary Duke, Alex Loukas, Donald P. McManus

Author Summary

Adult schistosomes live within portal veins of their human hosts. Their offspring, laid as eggs within the venous system, escape by traversing the tissues between the blood vessel and the gut or bladder lumen. Eggs voided into the external environment hatch spontaneously on contact with freshwater, and the hatched larva escapes in search of a snail, which acts as intermediate host of the parasite. In this study, we used correlative microscopy techniques to examine hatching of the larvae of Schistosoma japonicum. This species has an exquisite hatching behaviour, which allows us to trace the cellular changes in the egg that lead to hatching. By using a correlative microscopy approach, incorporating video microscopy, electron microscopy of eggs prepared by high pressure freezing and lectin immunocytochemistry, we were able to describe the pre-hatching state of the eggs, and trace changes that occur during hatching. The insights gained from these direct biological studies will be of value in understanding the host–parasite interplay of schistosome eggs in their hosts.

Enumeration of Mycobacterium leprae Using Real-Time PCR

2008-11-04T08:00:00Z

by Richard W. Truman, P. Kyle Andrews, Naoko Y. Robbins, Linda B. Adams, James L. Krahenbuhl, Thomas P. Gillis

Author Summary

Mycobacterium leprae is not cultivable in axenic media, and direct microscopic enumeration of the bacilli is complex, labor intensive, and suffers from limited sensitivity and specificity. We describe the use of real-time PCR to provide a rapid, objective and consistent enumeration procedure for M. leprae. The procedure is specific for M. leprae, has a dynamic range of approximately 6 logs and yields results in only a few hours, including processing time. The procedure was applied to M. leprae growing in mouse and armadillo tissues showing excellent correlation with microscopic counting. The benefits of this technique for experimental characterization of leprosy infections and vaccine trials are substantial, and potential applications to clinical specimens could impact patient management by simplifying the assessment of bacterial burden prior to and during drug treatment.

Diagnosis of Soil-Transmitted Helminths in the Era of Preventive Chemotherapy: Effect of Multiple Stool Sampling and Use of Different Diagnostic Techniques

2008-11-04T08:00:00Z

by Stefanie Knopp, Ali F. Mgeni, I. Simba Khamis, Peter Steinmann, J. Russell Stothard, David Rollinson, Hanspeter Marti, Jürg Utzinger

Author Summary

Diseases caused by parasitic worms inflict an enormous public health burden in developing countries. There is a growing effort to control worms with drugs. The success of repeated drug administrations can be assessed by measuring the decline in the prevalence and intensity of worm infections. Accurate diagnosis is a challenge, especially in areas with low infection intensities. We studied the effect of stool sampling efforts and the use of different diagnostic techniques on the measured prevalence of worms, including hookworm, large intestinal roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and dwarf threadworm (Strongyloides stercoralis) in Zanzibar, where worm control has been implemented over the past decade. Three early morning stool samples were collected from each of 342 schoolchildren on 3 consecutive days and analyzed with different techniques. The observed prevalence of the different worms increased with an enhanced sampling effort and when different diagnostic methods were combined. Examination of 3 stool samples per individual resulted in prevalences of T. trichiura, hookworm, A. lumbricoides, and S. stercoralis of 47.9%, 22.5%, 16.5%, and 10.8%, respectively. To conclude, the examination of multiple stool samples and the use of different techniques are recommended for accurate diagnosis of worms in areas undergoing repeated mass drug administration.

PLoS Neglected Tropical Diseases Issue Image | Vol. 2(10) October 2008

2008-10-29T07:00:00Z

Dengue virus is unable to productively infect dermal-type macrophages.

The image shows a human CD209⁺ macrophage, in which the dengue virus envelope E protein, fused to green fluorescent protein, is not co-localized with the acidic (red) perinuclear compartments. Envelope acidification is critical to initiate the viral life cycle. IL-10, present in the human skin, is required for the formation of these macrophages. Understanding these infection events shortly after the mosquito bite can help explain why many dengue infections are asymptomatic (see Kwan et al., doi:10.1371/journal.pntd.0000311).

Image Credit: Marion Decossas, Erika Navarro-Sanchez, and Hélène Dumortier

Marring Leishmaniasis: The Stigmatization and the Impact of Cutaneous Leishmaniasis in Pakistan and Afghanistan

2008-10-29T07:00:00Z

by Masoom Kassi, Mahwash Kassi, Abaseen Khan Afghan, Rabeea Rehman, Pashtoon Murtaza Kasi

Leishmaniases' Burden of Disease: Ways Forward for Getting from Speculation to Reality

2008-10-29T07:00:00Z

The CNCDs and the NTDs: Blurring the Lines Dividing Noncommunicable and Communicable Chronic Diseases

2008-10-29T07:00:00Z

by Peter J. Hotez, Abdallah S. Daar

Complexities of Assessing the Disease Burden Attributable to Leishmaniasis

2008-10-29T07:00:00Z

by Caryn Bern, James H. Maguire, Jorge Alvar

Among parasitic diseases, morbidity and mortality caused by leishmaniasis are surpassed only by malaria and lymphatic filariasis. However, estimation of the leishmaniasis disease burden is challenging, due to clinical and epidemiological diversity, marked geographic clustering, and lack of reliable data on incidence, duration, and impact of the various disease syndromes. Non-health effects such as impoverishment, disfigurement, and stigma add to the burden, and introduce further complexities. Leishmaniasis occurs globally, but has disproportionate impact in the Horn of Africa, South Asia and Brazil (for visceral leishmaniasis), and Latin America, Central Asia, and southwestern Asia (for cutaneous leishmaniasis). Disease characteristics and challenges for control are reviewed for each of these foci. We recommend review of reliable secondary data sources and collection of baseline active survey data to improve current disease burden estimates, plus the improvement or establishment of effective surveillance systems to monitor the impact of control efforts.

Stage- and Gender-Specific Proteomic Analysis of Brugia malayi Excretory-Secretory Products

2008-10-29T07:00:00Z

by Yovany Moreno, Timothy G. Geary

Author Summary

To succeed in infection, parasites must have ways to reach the host, penetrate its tissues and escape its defense systems. As they are not necessarily fatal, most helminth parasites remain viable within their host for many years, exerting a strong influence over the host immune function. Many of these functions are performed by products that are released from the parasite. We exploited the remarkable sensitivity of modern proteomics tools together with the availability of a sequenced genome to identify and compare the proteins released in vitro by adult males, adult females and the microfilariae of the filarial nematode Brugia malayi. This parasite is one of the etiological agents of lymphatic filariasis, a disease that poses continuing and significant threats to human health. The different forms of the parasite inhabit different compartments in the mammalian host. We found that the set of proteins released by each form is unique; they must reflect particular developmental processes and different strategies for evasion of host responses. The identification of these proteins will allow us to illuminate the biology of secretory processes in this organism and to establish a path for developing an understanding of how these parasite proteins function in immune evasion events.

A Simple Scoring System to Differentiate between Relapse and Re-Infection in Patients with Recurrent Melioidosis

2008-10-29T07:00:00Z

by Direk Limmathurotsakul, Wipada Chaowagul, Narisara Chantratita, Vanaporn Wuthiekanun, Mayurachat Biaklang, Sarinna Tumapa, Nicholas J. White, Nicholas P. J. Day, Sharon J. Peacock

Author Summary

Melioidosis is a serious infectious disease caused by the Gram-negative bacterium, Burkholderia pseudomallei. This organism is present in the environment in areas where melioidosis is endemic (most notably East Asia and Northern Australia), and infection is acquired following bacterial inoculation or inhalation. Despite prolonged oral eradicative treatment, recurrent melioidosis occurs in approximately 10% of survivors of acute melioidosis. Recurrent melioidosis can be caused by relapse (failure of initial eradicative treatment) or re-infection with a new infection. The aim of this study was to develop a simple scoring system to distinguish between re-infection and relapse, since this has implications for antimicrobial treatment of the recurrent episode, but telling the two apart normally requires bacterial genotyping. A prospective study of melioidosis patients in NE Thailand conducted between 1986 and 2005 identified 141 patients with recurrent melioidosis. Of these, 92 patients had relapse and 49 patients had re-infection as confirmed by genotyping techniques. We found that relapse was associated with previous inadequate treatment and shorter time to clinical features of recurrence, while re-infection was associated with renal insufficiency and presentation during the rainy season. A simple scoring index to help distinguish between relapse and re-infection was developed to provide important bedside information where rapid bacterial genotyping is unavailable. Guidelines are provided on how this scoring system could be implemented.

Web-Based Virtual Microscopy for Parasitology: A Novel Tool for Education and Quality Assurance

2008-10-22T07:00:00Z

by Ewert Linder, Mikael Lundin, Cecilia Thors, Marianne Lebbad, Jadwiga Winiecka-Krusnell, Heikki Helin, Byron Leiva, Jorma Isola, Johan Lundin

Author Summary

Here, we describe a novel tool to observe parasites by virtual microscopy on the Internet. Microscopy-based identification of parasites is the basis for both diagnostics and epidemiological assessment of parasite burden globally. Yet, quality assessment of diagnostic parasitology laboratories is difficult, as delivering identical educational specimens has been impossible. In this study, a series of parasite specimens on ordinary glass slides were digitized using a recently developed microscope scanner technique. Up to 50,000 images captured at high magnification are digitally stitched together to form a representation of the entire glass slide. These “virtual slides” digitized at a thousand-fold magnification can hold more than 60 gigabytes of data. Handling such large amounts of data was made possible because of efficient compression techniques and a viewing system adopted from the geospatial imaging industry. Viewing the samples on the Internet very much resembles, for example, the use of Google Maps, and puts only modest requirements on the viewer's computer. In addition, we captured image stacks at different focal planes, and developed a web-based viewing system for three-dimensional navigation in the specimens. This novel technique is especially valuable for detailed visualization of large objects such as helminth eggs in stool specimens.

Use of Genomic DNA as an Indirect Reference for Identifying Gender-Associated Transcripts in Morphologically Identical, but Chromosomally Distinct, Schistosoma mansoni Cercariae

2008-10-22T07:00:00Z

by Jennifer M. Fitzpatrick, Anna V. Protasio, Andrew J. McArdle, Gary A. Williams, David A. Johnston, Karl F. Hoffmann

Author Summary

Infection with parasitic schistosome worms causes schistosomiasis, a major neglected tropical disease currently affecting millions of individuals living in the developing world. A virtually unique characteristic of the schistosome life style in comparison to other members of the Phylum Platyhelminthes is that schistosomes are dioecious, having both male and female individuals. While much is known about the adult dioecious state, virtually nothing has been established with regard to the dioecious larval stages such as the snail-infective miracidium and the human-infective cercaria. To shed some light on this under-studied area of schistosome biology, we first developed a new long-oligonucleotide DNA microarray and used this tool to perfect an indirect hybridization strategy utilizing schistosome genomic DNA for large-scale transcription investigations. Second, we used this tool and strategy to characterize the gene expression profiles of infective male and female cercarial life-stages. This led to the identification of several thousand differentially expressed transcripts and demonstrated that gender-associated patterns of transcription (some associated with adult-specific activities) are surprisingly already established in this short-lived larval life-stage. Further functional interrogation of these transcripts will generate a more complete picture of factors and processes underlying the schistosome's dioecious state, which may help in control strategies attempting to prevent sexual maturation, inhibit male–female interactions and limit the production of tissue-damaging eggs.

Controlling Tungiasis in an Impoverished Community: An Intervention Study

2008-10-22T07:00:00Z

by Daniel Pilger, Stefan Schwalfenberg, Jörg Heukelbach, Lars Witt, Norbert Mencke, Adak Khakban, Hermann Feldmeier

Author Summary

Tungiasis is a disease caused by the sand flea Tunga penetrans, a parasite prevalent in many impoverished communities in developing countries. The female sand flea penetrates into the skin of animals and humans where it grows rapidly in size, feeds on the host's blood, produces eggs which are expelled into the environment, and eventually dies in situ. The lesions become frequently superinfected and the infestation is associated with considerable morbidity. Clearly, tungiasis is a neglected disease of neglected populations. We investigated the impact of a package of intervention measures targeted against on-host and off-host stages of T. penetrans in a fishing community in Northeast Brazil. These measures decreased disease occurrence only temporarily, but had a sustained effect on the intensity of the infestation. Since infestation intensity and morbidity are correlated, presumably the intervention also lowered tungiasis-associated morbidity. Control measures similar to the ones used in this study may help to effectively control tungiasis in impoverished communities.

Mycolactone Diffuses from Mycobacterium ulcerans–Infected Tissues and Targets Mononuclear Cells in Peripheral Blood and Lymphoid Organs

2008-10-22T07:00:00Z

by Hui Hong, Emmanuelle Coutanceau, Marion Leclerc, Laxmee Caleechurn, Peter F. Leadlay, Caroline Demangel

Author Summary

Mycolactone is a lipophilic molecule produced by Mycobacterium ulcerans, the causative agent of the skin disease Buruli ulcer (BU). Mycolactone displays unique cytocidal and immunosuppressive properties that are reflected locally by massive tissue necrosis and minimal inflammation. Here we investigated whether mycolactone diffuses from infected tissues and exerts immunosuppressive properties at the systemic level. We used both a radiolabeled form of the toxin and a direct LC-MS/MS analysis of lipid extracts from internal organs and cell subpopulations to investigate the pharmacodistribution of mycolactone in vivo. Using a mouse model of subcutaneous infection with M. ulcerans, we show that mycolactone distributes far beyond the sphere of its cytocidal action. The toxin diffused from infected tissues into the blood and the spleen, where it concentrated in mononuclear cell subsets. Importantly, mycolactone was detected in circulating blood several weeks before ulcerative lesions develop. The presence of mycolactone in blood cells was associated with a decreased capacity of circulating lymphocytes to produce interleukin-2 upon stimulation. In addition to providing the first evidence that mycolactone targets key immune cell populations in infected hosts, this work suggests that mycolactone detection in peripheral blood cells may form the basis of diagnostic tests of early disease.