PLoS Neglected Tropical Diseases News

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A Peer-Reviewed Open-Access Journal
Updated: 18 hours 41 min ago

The global burden of disease study 2013: What does it mean for the NTDs?

3 August 2017 - 9:00pm

by Jennifer R. Herricks, Peter J. Hotez, Valentine Wanga, Luc E. Coffeng, Juanita A. Haagsma, María-Gloria Basáñez, Geoffrey Buckle, Christine M. Budke, Hélène Carabin, Eric M. Fèvre, Thomas Fürst, Yara A. Halasa, Charles H. King, Michele E. Murdoch, Kapa D. Ramaiah, Donald S. Shepard, Wilma A. Stolk, Eduardo A. Undurraga, Jeffrey D. Stanaway, Mohsen Naghavi, Christopher J. L. Murray

Heterologous expression of the antimyotoxic protein DM64 in <i>Pichia pastoris</i>

31 July 2017 - 9:00pm

by Saulo Martins Vieira, Surza Lucia Gonçalves da Rocha, Ana Gisele da Costa Neves-Ferreira, Rodrigo Volcan Almeida, Jonas Perales

Snakebite envenomation is a neglected condition that constitutes a public health problem in tropical and subtropical countries, including Brazil. Interestingly, some animals are resistant to snake envenomation due to the presence of inhibitory glycoproteins in their serum that target toxic venom components. DM64 is an acidic glycoprotein isolated from Didelphis aurita (opossum) serum that has been characterized as an inhibitor of the myotoxicity induced by bothropic toxins bearing phospholipase A2 (PLA2) structures. This antitoxic protein can serve as an excellent starting template for the design of novel therapeutics against snakebite envenomation, particularly venom-induced local tissue damage. Therefore, the aim of this work was to produce a recombinant DM64 (rDM64) in the methylotrophic yeast Pichia pastoris and to compare its biological properties with those of native DM64. Yeast fermentation in the presence of Pefabloc, a serine protease inhibitor, stimulated cell growth (~1.5-fold), increased the rDM64 production yield approximately 10-fold and significantly reduced the susceptibility of rDM64 to proteolytic degradation. P. pastoris fermentation products were identified by mass spectrometry and Western blotting. The heterologous protein was efficiently purified from the culture medium by affinity chromatography (with immobilized PLA2 myotoxin) and/or an ion exchange column. Although both native and recombinant DM64 exhibit different glycosylation patterns, they show very similar electrophoretic mobilities after PNGase F treatment. rDM64 formed a noncovalent complex with myotoxin II (Lys49-PLA2) from Bothrops asper and displayed biological activity that was similar to that of native DM64, inhibiting the cytotoxicity of myotoxin II by 92% at a 1:1 molar ratio.

Control of chronic <i>Strongyloides stercoralis</i> infection in an endemic community may be possible by pharmacological means alone: Results of a three-year cohort study

31 July 2017 - 9:00pm

by Russell Hays, Adrian Esterman, Robyn McDermott


To assess the effect of treatment with ivermectin on the prevalence of S. stercoralis infection in an Australian Aboriginal population over a three year period, and to assess the validity of using a lower ELISA cut-off in diagnosis.


A three-year cohort study of 259 adult Australian Aboriginals living in a remote community in northern Australia. S stercoralis infection was diagnosed using commercial ELISA testing, and employed a lower threshold for treatment than that recommended. Follow up was conducted at 6 months and 3 years following ivermectin treatment.


Treatment with ivermectin was highly effective and resulted in a sustained fall in the prevalence of infection in the study group (Initial prevalence 35.3%, 3 year prevalence 5.8%, McNemar’s chi2 = 56.5, p<0.001). Results of treatment suggested use of a lower ELISA threshold for treatment was valid in this setting. Follow up identified a small group of subjects with persistently positive ELISA serology despite repeated treatment.


Control of S. stercoralis infection in this cohort appears to be feasible using pharmacological treatment alone.

Genome-wide diversity and differentiation in New World populations of the human malaria parasite <i>Plasmodium vivax</i>

31 July 2017 - 9:00pm

by Thais C. de Oliveira, Priscila T. Rodrigues, Maria José Menezes, Raquel M. Gonçalves-Lopes, Melissa S. Bastos, Nathália F. Lima, Susana Barbosa, Alexandra L. Gerber, Guilherme Loss de Morais, Luisa Berná, Jody Phelan, Carlos Robello, Ana Tereza R. de Vasconcelos, João Marcelo P. Alves, Marcelo U. Ferreira


The Americas were the last continent colonized by humans carrying malaria parasites. Plasmodium falciparum from the New World shows very little genetic diversity and greater linkage disequilibrium, compared with its African counterparts, and is clearly subdivided into local, highly divergent populations. However, limited available data have revealed extensive genetic diversity in American populations of another major human malaria parasite, P. vivax.


We used an improved sample preparation strategy and next-generation sequencing to characterize 9 high-quality P. vivax genome sequences from northwestern Brazil. These new data were compared with publicly available sequences from recently sampled clinical P. vivax isolates from Brazil (BRA, total n = 11 sequences), Peru (PER, n = 23), Colombia (COL, n = 31), and Mexico (MEX, n = 19).

Principal findings/Conclusions

We found that New World populations of P. vivax are as diverse (nucleotide diversity π between 5.2 × 10−4 and 6.2 × 10−4) as P. vivax populations from Southeast Asia, where malaria transmission is substantially more intense. They display several non-synonymous nucleotide substitutions (some of them previously undescribed) in genes known or suspected to be involved in antimalarial drug resistance, such as dhfr, dhps, mdr1, mrp1, and mrp-2, but not in the chloroquine resistance transporter ortholog (crt-o) gene. Moreover, P. vivax in the Americas is much less geographically substructured than local P. falciparum populations, with relatively little between-population genome-wide differentiation (pairwise FST values ranging between 0.025 and 0.092). Finally, P. vivax populations show a rapid decline in linkage disequilibrium with increasing distance between pairs of polymorphic sites, consistent with very frequent outcrossing. We hypothesize that the high diversity of present-day P. vivax lineages in the Americas originated from successive migratory waves and subsequent admixture between parasite lineages from geographically diverse sites. Further genome-wide analyses are required to test the demographic scenario suggested by our data.

Predicting spatial spread of rabies in skunk populations using surveillance data reported by the public

31 July 2017 - 9:00pm

by Kim M. Pepin, Amy J. Davis, Daniel G. Streicker, Justin W. Fischer, Kurt C. VerCauteren, Amy T. Gilbert


Prevention and control of wildlife disease invasions relies on the ability to predict spatio-temporal dynamics and understand the role of factors driving spread rates, such as seasonality and transmission distance. Passive disease surveillance (i.e., case reports by public) is a common method of monitoring emergence of wildlife diseases, but can be challenging to interpret due to spatial biases and limitations in data quantity and quality.

Methodology/Principal findings

We obtained passive rabies surveillance data from dead striped skunks (Mephitis mephitis) in an epizootic in northern Colorado, USA. We developed a dynamic patch-occupancy model which predicts spatio-temporal spreading while accounting for heterogeneous sampling. We estimated the distance travelled per transmission event, direction of invasion, rate of spatial spread, and effects of infection density and season. We also estimated mean transmission distance and rates of spatial spread using a phylogeographic approach on a subsample of viral sequences from the same epizootic. Both the occupancy and phylogeographic approaches predicted similar rates of spatio-temporal spread. Estimated mean transmission distances were 2.3 km (95% Highest Posterior Density (HPD95): 0.02, 11.9; phylogeographic) and 3.9 km (95% credible intervals (CI95): 1.4, 11.3; occupancy). Estimated rates of spatial spread in km/year were: 29.8 (HPD95: 20.8, 39.8; phylogeographic, branch velocity, homogenous model), 22.6 (HPD95: 15.3, 29.7; phylogeographic, diffusion rate, homogenous model) and 21.1 (CI95: 16.7, 25.5; occupancy). Initial colonization probability was twice as high in spring relative to fall.


Skunk-to-skunk transmission was primarily local (< 4 km) suggesting that if interventions were needed, they could be applied at the wave front. Slower viral invasions of skunk rabies in western USA compared to a similar epizootic in raccoons in the eastern USA implies host species or landscape factors underlie the dynamics of rabies invasions. Our framework provides a straightforward method for estimating rates of spatial spread of wildlife diseases.

Knowledge, attitudes and practices towards yaws and yaws-like skin disease in Ghana

31 July 2017 - 9:00pm

by Michael Marks, Cynthia Kwakye-Maclean, Rachel Doherty, Paul Adwere, Abdul Aziz Abdulai, Fredrick Duah, Sally-Ann Ohene, Oriol Mitja, Blanche Oguti, Anthony W. Solomon, David C. W. Mabey, Yaw Adu-Sarkodie, Kingsley Asiedu, Mercy M. Ackumey


Yaws is endemic in Ghana. The World Health Organization (WHO) has launched a new global eradication campaign based on total community mass treatment with azithromycin. Achieving high coverage of mass treatment will be fundamental to the success of this new strategy; coverage is dependent, in part, on appropriate community mobilisation. An understanding of community knowledge, attitudes and practices related to yaws in Ghana and other endemic countries will be vital in designing effective community engagement strategies.


A verbally administered questionnaire was administered to residents in 3 districts in the Eastern region of Ghana where a randomised trial on the treatment of yaws was being conducted. The questionnaire combined both quantitative and qualitative questions covering perceptions of the cause and mechanisms of transmission of yaws-like lesions, the providers from which individuals would seek healthcare for yaws-like lesions, and what factors were important in reaching decisions on where to seek care. Chi-square tests and logistic regression were used to assess relationships between reported knowledge, attitudes and practices, and demographic variables. Thematic analysis of qualitative data was used to identify common themes.


A total of 1,162 individuals participated. The majority of individuals (n = 895, 77%) reported that “germs” were the cause of yaws lesions. Overall 13% (n = 161) of respondents believed that the disease was caused by supernatural forces. Participants frequently mentioned lack of personal hygiene, irregular and inefficient bathing, and washing with dirty water as fundamental to both the cause and the prevention of yaws. A majority of individuals reported that they would want to take an antibiotic to prevent the development of yaws if they were asymptomatic (n = 689, 61.2%), but a substantial minority reported they would not want to do so. A majority of individuals (n = 839, 72.7%) reported that if they had a yaws-like skin lesion they would seek care from a doctor or nurse. Both direct and indirect costs of treatment were reported as key factors affecting where participants reported they would seek care.


This is the first study that has explored community knowledge, attitudes and practices in relation to yaws in any endemic population. The belief that ‘germs’ are in some way related to disease through a variety of transmission routes including both contact and dirty water are similar to those reported for other skin diseases in Ghana. The prominent role of private healthcare providers is an important finding of this study and suggests engagement with this sector will be important in yaws eradication efforts. Strategies to address the substantial minority of individuals who reported they would not take treatment for yaws if they were currently asymptomatic will be needed to ensure the success of yaws eradication efforts. The data collected will be of value to the Ghana Health Service and also to WHO and other partners, who are currently developing community mobilisation tools to support yaws eradication efforts worldwide.

Prevalence of <i>Toxocara</i> species infection in the U.S.: Results from the National Health and Nutrition Examination Survey, 2011-2014

31 July 2017 - 9:00pm

by Aaron Farmer, Thomas Beltran, Young Sammy Choi

Toxocariasis is one of the most common neglected infections of poverty in the U.S. with a reported National Health and Nutrition Examination Survey (NHANES) III (1988–1994) seroprevalence of 13.9% based on enzyme immunoassay testing. We reviewed NHANES data from 2011–2014 to assess current levels. Sera collected from NHANES 2011–2014 participants six years and older were tested for exposure using rTc-CTL-1 antigen, a more sensitive and specific recombinant antigen for IgG antibodies for Toxocara spp. These results were subdivided into children (age 6–17) and adults (age ≥ 18) and then compared between various sociodemographic characteristics. Given prior associations of Toxocara exposure with atopic disease and lead exposure, we also reviewed laboratory values including complete blood counts and blood and urine lead levels. Data from 13,509 individuals with Toxocara antibody results were examined including 3337 children (15.2%) and 10172 adults (84.8%). Overall seroprevalence was 5.1%. In adults increased antibody positivity occurred with non-White ethnicity, male gender, less than college-level education and lower income. Among children, increased antibody positivity was solely related to a lack of health insurance. Additionally, seropositivity was associated with increased blood lead and eosinophil levels in adults and both blood and urine lead levels in children. Relative to NHANES III (1988–1994), current data suggest an overall decrease in Toxocara spp. seroprevalence from 13.9% to 5.1%, however this may be artificially lowered due to difference in testing methods used. Persistent disparities appear to be associated with at-risk populations such as minority ethnicity and low socioeconomic status.

Mixed Th1 and Th2 <i>Mycobacterium tuberculosis</i>-specific CD4 T cell responses in patients with active pulmonary tuberculosis from Tanzania

31 July 2017 - 9:00pm

by Patrizia Amelio, Damien Portevin, Klaus Reither, Francis Mhimbira, Maxmillian Mpina, Anneth Tumbo, Beatrice Nickel, Hanspeter Marti, Stefanie Knopp, Song Ding, Adam Penn-Nicholson, Fatoumatta Darboe, Khalid Ohmiti, Thomas J. Scriba, Giuseppe Pantaleo, Claudia Daubenberger, Matthieu Perreau

Mycobacterium tuberculosis (Mtb) and helminth infections elicit antagonistic immune effector functions and are co-endemic in several regions of the world. We therefore hypothesized that helminth infection may influence Mtb-specific T-cell immune responses. We evaluated the cytokine profile of Mtb-specific T cells in 72 individuals with pulmonary TB disease recruited from two Sub-Saharan regions with high and moderate helminth burden i.e. 55 from Tanzania (TZ) and 17 from South Africa (SA), respectively. We showed that Mtb-specific CD4 T-cell functional profile of TB patients from Tanzania are primarily composed of polyfunctional Th1 and Th2 cells, associated with increased expression of Gata-3 and reduced expression of T-bet in memory CD4 T cells. In contrast, the cytokine profile of Mtb-specific CD4 T cells of TB patients from SA was dominated by single IFN-γ and dual IFN-γ/TNF-α and associated with TB-induced systemic inflammation and elevated serum levels of type I IFNs. Of note, the proportion of patients with Mtb-specific CD8 T cells was significantly reduced in Mtb/helminth co-infected patients from TZ. It is likely that the underlying helminth infection and possibly genetic and other unknown environmental factors may have caused the induction of mixed Th1/Th2 Mtb-specific CD4 T cell responses in patients from TZ. Taken together, these results indicate that the generation of Mtb-specific CD4 and CD8 T cell responses may be substantially influenced by environmental factors in vivo. These observations may have major impact in the identification of immune biomarkers of disease status and correlates of protection.

Proteogenomic analysis of the total and surface-exposed proteomes of <i>Plasmodium vivax</i> salivary gland sporozoites

31 July 2017 - 9:00pm

by Kristian E. Swearingen, Scott E. Lindner, Erika L. Flannery, Ashley M. Vaughan, Robert D. Morrison, Rapatbhorn Patrapuvich, Cristian Koepfli, Ivo Muller, Aaron Jex, Robert L. Moritz, Stefan H. I. Kappe, Jetsumon Sattabongkot, Sebastian A. Mikolajczak

Plasmodium falciparum and Plasmodium vivax cause the majority of human malaria cases. Research efforts predominantly focus on P. falciparum because of the clinical severity of infection and associated mortality rates. However, P. vivax malaria affects more people in a wider global range. Furthermore, unlike P. falciparum, P. vivax can persist in the liver as dormant hypnozoites that can be activated weeks to years after primary infection, causing relapse of symptomatic blood stages. This feature makes P. vivax unique and difficult to eliminate with the standard tools of vector control and treatment of symptomatic blood stage infection with antimalarial drugs. Infection by Plasmodium is initiated by the mosquito-transmitted sporozoite stage, a highly motile invasive cell that targets hepatocytes in the liver. The most advanced malaria vaccine for P. falciparum (RTS,S, a subunit vaccine containing of a portion of the major sporozoite surface protein) conferred limited protection in Phase III trials, falling short of WHO-established vaccine efficacy goals. However, blocking the sporozoite stage of infection in P. vivax, before the establishment of the chronic liver infection, might be an effective malaria vaccine strategy to reduce the occurrence of relapsing blood stages. It is also thought that a multivalent vaccine comprising multiple sporozoite surface antigens will provide better protection, but a comprehensive analysis of proteins in P. vivax sporozoites is not available. To inform sporozoite-based vaccine development, we employed mass spectrometry-based proteomics to identify nearly 2,000 proteins present in P. vivax salivary gland sporozoites. Analysis of protein post-translational modifications revealed extensive phosphorylation of glideosome proteins as well as regulators of transcription and translation. Additionally, the sporozoite surface proteins CSP and TRAP, which were recently discovered to be glycosylated in P. falciparum salivary gland sporozoites, were also observed to be similarly modified in P. vivax sporozoites. Quantitative comparison of the P. vivax and P. falciparum salivary gland sporozoite proteomes revealed a high degree of similarity in protein expression levels, including among invasion-related proteins. Nevertheless, orthologs with significantly different expression levels between the two species could be identified, as well as highly abundant, species-specific proteins with no known orthologs. Finally, we employed chemical labeling of live sporozoites to isolate and identify 36 proteins that are putatively surface-exposed on P. vivax salivary gland sporozoites. In addition to identifying conserved sporozoite surface proteins identified by similar analyses of other Plasmodium species, our analysis identified several as-yet uncharacterized proteins, including a putative 6-Cys protein with no known ortholog in P. falciparum.

Risk factors for inadequate antibody response to primary rabies vaccination in dogs under one year of age

31 July 2017 - 9:00pm

by Ryan M. Wallace, Anna Pees, Jesse B. Blanton, Susan M. Moore

Ensuring the adequacy of response to rabies vaccination in dogs is important, particularly in the context of pet travel. Few studies have examined the factors associated with dogs’ failure to achieve an adequate antibody titer after vaccination (0.5 IU/ml). This study evaluated rabies antibody titers in dogs after primary vaccination. Dogs under one year of age whose serum was submitted to a reference laboratory for routine diagnostics, and which had no prior documented history of vaccination were enrolled (n = 8,011). Geometric mean titers (GMT) were calculated and univariate analysis was performed to assess factors associated with failure to achieve 0.5 IU/mL. Dogs vaccinated at >16 weeks of age had a significantly higher GMT compared to dogs vaccinated at a younger age (1.64 IU/ml, 1.57–1.72, ANOVA p < 0.01). There was no statistical difference in GMT between dogs vaccinated <12 weeks and dogs vaccinated 12–16 weeks (1.22 IU/ml and 1.21 IU/ml). The majority of dogs failed to reach an adequate titer within the first 3 days of primary vaccination; failure rates were also high if the interval from vaccination to titer check was greater than 90 days. Over 90% of dogs that failed primary vaccination were able to achieve adequate titers after booster vaccination. The ideal timing for blood draw is 8–30 days after primary vaccination. In the event of a failure, most dogs will achieve an adequate serologic response upon a repeat titer (in the absence of booster vaccination). Booster vaccination after failure provided the highest probability of an acceptable titer.