Forty-four Schistosoma mansoni egg-negative/circulating cathodic antigen (CCA) low-positive (trace or 1+) children in three districts of very low prevalence in Egypt were given three sequential praziquantel (PZQ) treatments. Stool and urine specimens were collected 3 months following the initial treatment, and 3 weeks following the second and following the third PZQ treatments, which were conducted 5 weeks apart. Stool specimens were examined by Kato-Katz (four slides/stool sample) and all S. mansoni egg-negative stools were further tested by the “miracidia hatching test” (MHT). Urine samples were examined by the point-of-care CCA assay (POC-CCA). Over the study period, all stool samples from study subjects remained S. mansoni egg negative and MHT negative. Of the POC-CCA test results, in the first day of the study 3 months following the initial treatment, 29.5% were negative, 61.4% CCA trace positives, and 9.1% CCA 1+ positives. Following each PZQ treatment, the test results fluctuated between 1+, trace, and negative, but did not consistently decrease. The proportions of POC-CCA-positive results obtained in the first day (70.5%) as compared with the last day of the study (72.7%) in all of the three districts were very similar. We conclude that CCA trace and 1+ readings, in Kato-Katz S. mansoni egg-negative children in this area with very low levels of intestinal schistosomiasis, are not consistently altered or rendered consistently negative following repeated PZQ treatments and are therefore likely to represent false-positive readings. This finding is of critical importance for countries such as Egypt as they approach elimination.
Ayat A. Haggag, Miriam Casacuberta Partal, Amal Rabiee, Khaled M. Abd Elaziz, Carl H. Campbell Jr., Daniel G. Colley and Reda M. R. Ramzy. 2019. Am J Trop Med Hyg. doi: 10.4269/ajtmh.18-0961
Despite significant progress, China faces the challenge of re-emerging schistosomiasis transmission in currently controlled areas due, in part, to the presence of a range of animal reservoirs, notably water buffalo and cattle, which can harbor Schistosoma japonicuminfections. Environmental, ecological and social-demographic changes in China, shown to affect the distribution of oncomelanid snails, can also impact future schistosomiasis transmission. In light of their importance in the S. japonicum, lifecycle, vaccination has been proposed as a means to reduce the excretion of egg from cattle and buffalo, thereby interrupting transmission from these reservoir hosts to snails. A DNA-based vaccine (SjCTPI) our team developed showed encouraging efficacy against S. japonicum in Chinese water buffaloes. Here we report the results of a double-blind cluster randomized trial aimed at determining the impact of a combination of the SjCTPI bovine vaccine (given as a prime-boost regimen), human mass chemotherapy and snail control on the transmission of S. japonicum in 12 selected administrative villages around the Dongting Lake in Hunan province. The trial confirmed human praziquantel treatment is an effective intervention at the population level. Further, mollusciciding had an indirect ~50% efficacy in reducing human infection rates. Serology showed that the SjCTPI vaccine produced an effective antibody response in vaccinated bovines, resulting in a negative correlation with bovine egg counts observed at all post-vaccination time points. Despite these encouraging outcomes, the effect of the vaccine in preventing human infection was inconclusive. This was likely due to activities undertaken by the China National Schistosomiasis Control Program, notably the treatment, sacrifice or removal of bovines from trial villages, over which we had no control; as a result, the trial design was compromised, reducing power and contaminating outcome measures. This highlights the difficulties in undertaking field trials of this nature and magnitude, particularly over a long period, and emphasizes the importance of mathematical modeling in predicting the potential impact of control intervention measures. A transmission blocking vaccine targeting bovines for the prevention of S. japonicum with the required protective efficacy would be invaluable in tandem with other preventive intervention measures if the goal of eliminating schistosomiasis from China is to become a reality.
Gail M. Williams, Yue-Sheng Li, Darren J. Gray, Zheng-Yuan Zhao, Donald A. Harn, Lisa M. Shollenberger, Sheng-Ming Li, Xinglin Yu, Zeng Feng, Jia-Gang Guo, Jie Zhou, Yu-Lan Dong, Yuan Li, Biao Guo, Patrick Driguez, Marina Harvie, Hong You, Allen G. Ross and Donald P. McManus. Front Immunol. 2019 Apr 3;10:645. doi: 10.3389/fimmu.2019.006452019.
The population of Brazil is currently characterised by many individuals harbouring low-intensity Schistosoma mansoni infections. The Kato-Katz technique is the diagnostic method recommended by the World Health Organization (WHO) to assess these infections, but this method is not sensitive enough in the context of low egg excretion. In this regard, potential alternatives are being employed to overcome the limits of the Kato-Katz technique. In the present review, we evaluated the performance of parasitological and immunological approaches adopted in Brazilian areas. Currently, the diagnostic choices involve a combination of strategies, including the utilisation of antibody methods to screen individuals and then subsequent confirmation of positive cases by intensive parasitological investigations.
Vanessa Silva-Moraes, Lisa M Shollenberger, Liliane Maria Vidal Siqueira, William Castro-Borges, Donald A Harn, Rafaella Fortini Queiroz e Grenfell, Ana Lucia Teles Rabello, Paulo Marcos Zech Coelho. 2019. Mem Inst Oswaldo Cruz. 2019 Mar 28;114:e180478. doi: 10.1590/0074-02760180478.
Despite decades of use of control programs, schistosomiasis remains a global public health problem. To further reduce prevalence and intensity of infection, or to achieve the goal of elimination in low-endemic areas, there needs to be better diagnostic tools to detect low-intensity infections in low-endemic areas in Brazil. The rationale for development of new diagnostic tools is that the current standard test Kato-Katz (KK) is not sensitive enough to detect low-intensity infections in low-endemic areas. In order to develop new diagnostic tools, we employed a proteomics approach to identify biomarkers associated with schistosome-specific immune responses in hopes of developing sensitive and specific new methods for immunodiagnosis.
METHODS AND FINDINGS:
Immunoproteomic analyses were performed on egg extracts of Schistosoma mansoni using pooled sera from infected or non-infected individuals from a low-endemic area of Brazil. Cross reactivity with other soil-transmitted helminths (STH) was determined using pooled sera from individuals uniquely infected with different helminths. Using this approach, we identified 23 targets recognized by schistosome acute and chronic sera samples. To identify immunoreactive targets that were likely glycan epitopes, we compared these targets to the immunoreactivity of spots treated with sodium metaperiodate oxidation of egg extract. This treatment yielded 12/23 spots maintaining immunoreactivity, suggesting that they were protein epitopes. From these 12 spots, 11 spots cross-reacted with sera from individuals infected with other STH and 10 spots cross-reacted with the negative control group. Spot number 5 was exclusively immunoreactive with sera from S. mansoni-infected groups in native and deglycosylated conditions and corresponds to Major Egg Antigen (MEA). We expressed MEA as a recombinant protein and showed a similar recognition pattern to that of the native protein via western blot. IgG-ELISA gave a sensitivity of 87.10% and specificity of 89.09% represented by area under the ROC curve of 0.95. IgG-ELISA performed better than the conventional KK (2 slides), identifying 56/64 cases harboring 1-10 eggs per gram of feces that were undiagnosed by KK parasitological technique.
CONCLUSIONS:
The serological proteome approach was able to identify a new diagnostic candidate. The recombinant egg antigen provided good performance in IgG-ELISA to detect individuals with extreme low-intensity infections (1 egg per gram of feces). Therefore, the IgG-ELISA using this newly identified recombinant MEA can be a useful tool combined with other techniques in low-endemic areas to determine the true prevalence of schistosome infection that is underestimated by the KK method. Further, to overcome the complexity of ELISA in the field, a second generation of antibody-based rapid diagnostic tests (RDT) can be developed.
Vanessa Silva-Moraes, Lisa Marie Shollenberger, William Castro-Borges, Ana Lucia Teles Rabello, Donald A. Harn, Lia Carolina Soares Medeiros, Wander de Jesus Jeremias, Liliane Maria Vidal Siqueira, Caroline Stephane Salviano Pereira, Maria Luysa Camargos Pedrosa, Nathalie Bonatti Franco Almeida, Aureo Almeida, Jose Roberto Lambertucci, Nídia Francisca de Figueiredo Carneiro, Paulo Marcos Zech Coelho, Rafaella Fortini Queiroz Grenfell. 2019. PLOS Neglected Tropical Diseases. https://doi.org/10.1371/journal.pntd.0006974
Forty-five Schistosoma mansoni egg–negative/circulating cathodic antigen (CCA) low (Trace-1+) positive children in areas of very low prevalence were followed up daily for 30 days. Stool and urine specimens were collected and examined each day from each child. At the midpoint of the study, three egg-positive control persons with light intensity infection were included in the protocol. Stool samples were examined by the Kato–Katz (four slides/stool sample) technique and all S. mansoni egg–negative stools were further tested by the “miracidia hatching test” (MHT). Urine samples were examined by the point-of-care CCA assay (POC-CCA). Over 30 days, only one of 1,338 consecutive stool samples from study subjects was S. mansoni egg and MHT positive (0.07%). Egg counts fluctuated daily in stools from positive controls and S. mansoni miracidia were detected in all but two samples by the MHT. Point-of-care–circulating cathodic antigen bands were scored from G1 to G10 and then translated to standard Trace, 1+, 2+, 3+ banding patterns. In two districts, the POC-CCA assays were Trace or 1+ for both the study children and the positive controls. In the third district, the POC-CCA assays were Trace or 1+ for the study children and 1+ or 2+ for the positive control. We conclude that in areas with extremely low prevalence S. mansoni egg–negative and CCA-Trace or 1+ children are unlikely to pose substantial risks to continued transmission of schistosomiasis. In this setting, POC-CCA Trace or 1+ readings are likely to be false positives or perhaps represent low-level single-sex schistosome infections.
The World Health Organization (WHO) has defined goals for schistosomiasis morbidity control to be reached by 2025 that are based on preventive chemotherapy. Intervention thresholds for Schistosoma mansoni are currently defined for prevalence measured by stool microscopy using the Kato-Katz technique. However, the Kato-Katz technique shows low sensitivity, particularly for the detection of light-intensity infections. Replacing it with the semi-quantitative point-of-care circulating cathodic antigen (POC-CCA) urine cassette test requires translation of the thresholds and precise characterization of the diagnostic sensitivity and specificity. In this study, we applied a novel egg-count model to a suite of data obtained from different settings in Africa and the Americas with diverse endemicity levels. We used a simulation study to infer on the relation between Kato-Katz and POC-CCA prevalence. Based on our study, we were able to provide recommendations for POC-CCA thresholds taking into account semi-quantitative results of the test. We found that a S. mansoni prevalence of 10% based on duplicate slide Kato-Katz thick smear is equivalent to 15–40% POC-CCA prevalence when trace results are considered positive and to 10–20% POC-CCA prevalence when trace results are considered negative. Our results have important bearings for mapping, control, surveillance, and verification of elimination of intestinal schistosomiasis.
Oliver Bärenbold, Amadou Garba, Daniel G. Colley, Fiona M. Fleming, Ayat A. Haggag, Reda M. R. Ramzy, Rufin K. Assaré, Edridah M. Tukahebwa, Jean B. Mbonigaba, Victor Bucumi, Biruck Kebede, Makoy S. Yibi, Aboulaye Meité, Jean T. Coulibaly, Eliézer K. N’Goran, Louis-Albert Tchuem Tchuenté, Pauline Mwinzi, Jürg Utzinger, Penelope Vounatsou. 2018. PLOS Neglected Tropical Diseases. https://doi.org/10.1371/journal.pntd.0006941
Daniel Colley visits a car wash in Kisumu, Kenya, one of his study sites for more than 20 years. Workers at the car wash drive vehicles into Lake Victoria, infecting and reinfecting themselves with schistosomiasis. (Photo courtesy of SCORE)
One day Daniel Colley raised his hand to volunteer, setting in motion five decades of scientific adventures. It was 1969, and Colley’s postdoctoral adviser, Byron Waksman, a renowned immunologist at Yale University School of Medicine, had stepped into the laboratory and asked if anyone wanted to go to Brazil.
“I have no idea why my hand shot up,” says Colley. “I didn’t know anything about Brazil. My wife and I didn’t even have passports. I asked Byron about the nature of the research, and he said, ‘Schistosomiasis.’ My response was, ‘What’s that?’”
Colley, today a UGA immunologist and Fellow of the American Association for the Advancement of Science, became fascinated by schistosomiasis, a parasitic worm infection plaguing poverty-stricken communities in sub-Saharan Africa and around the world. Globally more than 250 million people are infected via contact with water that carries the parasites.
The waterborne worms penetrate human skin and take up residence in blood vessels. About 5 to 10 percent of infections progress to life-threatening disease over decades. But most people experience more subtle symptoms such as fatigue, anemia, wasting, malnutrition and impaired cognitive development.
“Children playing in the water are picking up these chronic parasitic infections,” he says, “so they are sick and don’t do as well in school. If kids don’t receive what they need to develop early in life, it can become a lifelong disability.”
This irrigation channel in a village in Niger is a schistosomiasis transmission site. The children exposed there were tested and treated as part of the Schistosomiasis Consortium for Operational Research and Evaluation program, led by Colley. (Photo by Amadou Garba/SCORE)
After his Brazil sojourn, Colley arrived at Vanderbilt University in 1971, setting up a lab and beginning his career-long effort to understand the immunological paradox of schistosomiasis (or “schisto,” in the vernacular).
“The more I learned about schisto, the more interesting it became,” says Colley, who tweets as @SchistoKid. “It has a bizarre life cycle. Here’s a worm that can live inside your blood vessels for up to 40 years, though more typically it lasts for five to 10 years. Why doesn’t your immune system get rid of this creature sooner? That was a very intriguing question.”
In infected human blood vessels, the female worms produce eggs that the male fertilizes. Many of the eggs escape the human body in urine or feces. When people urinate or defecate in or near fresh water, the eggs can infect freshwater snails, where the parasite develops and rapidly multiplies. When worms re-enter fresh water, they can find human victims.
Meanwhile, the body’s remaining worm eggs are swept by the bloodstream into the gut wall and the liver or bladder, where they become lodged. The immune system fights these egg intruders with a delicate, two-pronged effort: First, masses of cells called granulomas wall off the eggs, isolating them from surrounding tissue and reducing disease. But the immune system must also regulate granuloma growth. For most people, this regulatory response keeps granulomas relatively small, but some grow over decades, eventually causing fibrosis and blocking blood flow through the liver, causing internal bleeding.
“Schisto is a very complex puzzle for an immunologist,” Colley says. “If you fail to have the initial immune response against the egg, you die. But if you fail to regulate this immune response against the egg over time, you die. How our immune system has co-evolved with schisto is fascinating to me, and I still haven’t figured out how it’s done.”
In 1992, he joined the Centers for Disease Control and Prevention and a year later was promoted to director of its Division of Parasitic Diseases. “I learned about a lot of other parasitic diseases. It was an incredibly broadening experience that became useful in my later work at UGA. From my colleagues, I gained knowledge in epidemiology—the incidence and prevalence of diseases and detecting the sources and causes of epidemics.”
He arrived at UGA in 2001 as professor of microbiology and director of the Center for Tropical and Emerging Global Diseases, created only three years before. “UGA started the center and took risks by investing in it,” he says. “Now it’s globally famous for its work in parasitic diseases and has 23 principal investigators.”
During the past decade, Colley has been director of UGA’s Schistosomiasis Consortium for Operational Research and Evaluation (SCORE), a program supported by the Bill & Melinda Gates Foundation. SCORE scientists study strategies used in eight sub-Saharan African countries to control and eventually eliminate schistosomiasis. Today, most sub-Saharan African governments collaborate with the World Health Organization and a pharmaceutical company to provide a free drug, praziquantel, that treats existing infections and can significantly reduce new cases.
“SCORE has shown that mass interventions with praziquantel do work, and they are best done every year,” he says. SCORE researchers also helped develop a more rapid and precise diagnostic test for schistosomiasis, discovering many more cases in children than previously thought.
“The main message I’ve learned in my career is that diseases such as schisto are diseases of poverty,” he says. “Poverty contributes to these diseases, and poverty is also the result of them. If you are a stunted kid, and you have anemia, and your cognitive development is not great because of a parasite, it’s harder to succeed.
“People are the same everywhere—they all want a better life, and in some places, that’s not happening. Fighting these infections is an important part of making lives better.”
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Originally published at UGA Research.
Parasitologic surveys of young adults in college and university settings are not commonly done, even in areas known to be endemic for schistosomiasis and soil-transmitted helminths. We have done a survey of 291 students and staff at the Kisumu National Polytechnic in Kisumu, Kenya, using the stool microscopy Kato-Katz (KK) method and the urine point-of-care circulating cathodic antigen (POC-CCA) test. Based on three stools/two KK slides each, in the 208 participants for whom three consecutive stools were obtained, Schistosoma mansoni prevalence was 17.8%. When all 291 individuals were analyzed based on the first stool, as done by the national neglected tropical disease (NTD) program, and one urine POC-CCA assay (n = 276), the prevalence was 13.7% by KK and 23.2% by POC-CCA. Based on three stools, 2.5% of 208 participants had heavy S. mansoni infections (≥400 eggs/gram feces), with heavy S. mansoni infections making up 13.5% of the S. mansoni cases. The prevalence of the soil-transmitted helminths (STH: Ascaris lumbricoides, Trichuris trichiura and hookworm) by three stools was 1.4%, 3.1%, and 4.1%, respectively, and by the first stool was 1.4%, 2.4% and 1.4%, respectively. This prevalence and intensity of infection with S. mansoni in a college setting warrants mass drug administration with praziquantel. This population of young adults is ‘in school’ and is both approachable and worthy of inclusion in national schistosomiasis control and elimination programs.
Harrison K. Korir, Diana K. Riner, Emmy Kavere, Amos Omondi, Jasmine Landry, Nupur Kittur, Eric M. Ndombi, Bartholomew N. Ondigo, W. Evan Secor, Diana M. S. Karanja and Daniel G. Colley. 2018. Trop. Med. Infect. Dis.; 3(3):100. https://doi.org/10.3390/tropicalmed3030100
The stated goal of the World Health Organization’s program on schistosomiasis is paraphrased as follows: to control morbidity and eliminate transmission where feasible. Switching from a goal of controlling morbidity to interrupting transmission may well be currently feasible in some countries in the Caribbean, some areas in South America, northern Africa, and selected endemic areas in sub-Saharan Africa where there have been improvements in sanitation and access to clean water. However, in most of sub-Saharan Africa, where programmatic interventions still consist solely of annual mass drug administration, such a switch in strategies remains premature. There is a continued need for operational research on how best to reduce transmission to a point where interruption of transmission may be achievable. The level of infection at which it is feasible to transition from control to elimination must also be defined. In parallel, there is also a need to develop and evaluate approaches for achieving and validating elimination. There are currently neither evidence-based methods nor tools for breaking transmission or verifying that it has been accomplished. The basis for these statements stems from numerous studies that will be reviewed and summarized in this article; many, but not all of which were undertaken as part of SCORE, the Schistosomiasis Consortium for Operational Research and Evaluation
