Hit Me Again (with Another Mutation)

One of the best tests of character as a scientist is how you respond when a colleague asks you a pointed question that you don’t have a great response for. This is especially true when different colleagues ask you the same question. For me, that inquiry has been, “Why doesn’t your mouse model of urogenital schistosomiasis result in bladder cancer?”

Before I delve into why this observant question is painful for me, I should rewind and paint the backdrop associated with this recurring query. Urogenital schistosomiasis, infection by parasitic Schistosoma haematobium worms, affects approximately 112 million people worldwide. Most of the burden of disease is in sub-Saharan Africa, with some distribution in the Middle East, and possibly even parts of Mediterranean Europe. Urogenital schistosomiasis causes an incredible range of human disease, but perhaps its most notorious manifestation is bladder cancer.

Although urogenital schistosomiasis is an accepted risk factor for bladder cancer, and in fact may be one of the most important risk factors besides smoking, the biological pathways linking S. haematobium infection to bladder carcinogenesis are poorly understood. This is in no small part due to the fact that traditionally, animal models for urogenital schistosomiasis have been lacking. Hamsters can be infected with S. haematobium, but they almost always develop liver and intestinal disease, rather than bladder infection like that seen in humans. Non-human primates are biologically compatible hosts for S. haematobium, but they are very expensive and their use is coming under increasing scrutiny due to ethical considerations. There are also very few scientific tools specifically geared towards use with hamsters and non-human primates, which further exacerbates the problem. In contrast, although there is a large array of scientific tools to study mouse biology, mice, like hamsters, develop liver and intestinal disease after S. haematobium infection.

To attempt to circumvent these barriers to urogenital schistosomiasis research we developed techniques to inject S. haematobium eggs, the parasite life stage which triggers human bladder changes, into the bladder walls of mice (Fu et al.). This approach recapitulates many of the changes seen in the human bladder infected by S. haematobium (reviewed by Payne and Hsieh), including urothelial hyperplasia and squamous metaplasia of the inner lining of the bladder:

Schistosoma haematobium eggs may induce mouse bladder preneoplasia. (A–C) Egg injection of the mouse bladder wall induces early and sustained urothelial hyperplasia (urothelium >3 cells thick) with reactive nuclear changes. Adapted from Fu et al. (D) Egg injection of the mouse bladder wall also induces squamous metaplasia, with typical signs of very fine, stratum spinosum-like spiny projections between cobblestone-resembling urothelial cells with foamy cytoplasm. Urothelial hyperplasia and squamous metaplasia may be preneoplastic lesions, in that they may be necessary but not sufficient for frank bladder carcinogenesis. Adapted from Honeycutt et al.

The squamous metaplasia seen in our mouse model is relevant, given that similar findings are observed in many human bladders with squamous cell carcinoma, an otherwise unusual form of bladder cancer that is highly prevalent in schistosomiasis-endemic regions:

Schistosoma haematobium-associated bladder squamous metaplasia and carcinoma. Micrographs from stained sections of a bladder with keratinized, moderately differentiated squamous cell carcinoma associated with urogenital schistosomiasis. (A) Low power view of bladder section. (B) High power view of area indicated by broken line box in (A) demonstrating squamous metaplasia of the urothelium with infiltration of the lamina propria by a large number of S. haematobium ova (several eggs are circled as examples). In this specimen, the squamous metaplasia is evident as a hyperkeratotic squamous epithelium (arrow) lining the bladder lumen. (C) Another region of the same bladder exhibits abundant keratin pearls (examples indicated by arrows), a classic sign of squamous cell carcinoma. Adapted from Honeycutt et al.

Importantly, our mouse model indeed does not result in frank bladder carcinogenesis, despite the development of potentially pre-cancerous changes such as squamous metaplasia and urothelial hyperplasia. There are a number of plausible reasons why this is the case. First, our mouse model features a single injection of eggs into the bladder wall. Egg deposition in infected humans occurs continuously over the course of years to decades. By definition, our approach cannot reproduce the kinetics of human infection. Since cancer is a very chronic disease that develops slowly, and the life span of mice is measured in a few years at best, it is also likely that even with continuous egg deposition, mice may not live long enough to develop bladder cancer. Finally, we may not be seeing bladder cancers developing in our mouse model because cancer in general requires “multiple hits”. It is rare for cancer to develop in a given person unless they have, for example, both genetic susceptibility and exposure to carcinogens (i.e., smoking, excessive red meat intake, etc.). In short, people’s bodies need to be “hit” again and again by genetic mutations that accumulate and eventually result in cancer. By analogy, it may be necessary for people with urogenital schistosomiasis to have additional environmental exposures and/or genetic predisposition in order for them to develop bladder cancer. Otherwise, there would literally be tens of millions of people in sub-Saharan Africa with schistosomal bladder cancer.

When asked about why my mouse model doesn’t result in bladder cancer, I don’t go through all the points I’ve listed above. I tailor the answer to the interest level and scientific background of the questioner, but ultimately the deeper question is not whether multiple hits are required for schistosomal bladder cancer to ensue, but which ones and when. If I can contribute just a little bit to understanding how this occurs, that’s a hit that I’ll take.


Fu CL, Apelo CA, Torres B, Thai KH, & Hsieh MH (2011). Mouse bladder wall injection. Journal of visualized experiments : JoVE (53) PMID: 21775962

Payne R, & Hsieh M (2012). Reinforcements arrive for the war against chronic cystitis and bladder cancer. BJU international, 110 (9), 1223-4 PMID: 22882427

Honeycutt J, Hammam O, Fu CL, & Hsieh MH (2014). Controversies and challenges in research on urogenital schistosomiasis-associated bladder cancer. Trends in parasitology PMID: 24913983

Doctor and Commander

Dear Friends/Colleagues,
As I get closer to becoming the inaugural Stirewalt Endowed Director of the Biomedical Research Institute (BRI), I’d like to introduce you to Dr. Stirewalt and her seminal work.

Margaret A. Stirewalt (later Lincicome), was born in 1911 and died in 2003. “Peg”, as she was known to those familiar with her, earned her BA at Randolph-Macon Woman’s College, Lynchburg, Virginia, in 1931, her MA at Columbia University, New York, in 1935, and her PhD from the University of Virginia in 1938. She was a Commander in the Navy and a Naval Medical Officer at the Naval Medical Research Institute and a scientist at the Biomedical Research Institute (BRI). Dr. Stirewalt had a distinguished career in teaching and research in schistosomes, which are some of the worst human-specific parasites on the planet. These accomplishments are all the more remarkable considering the era that Dr. Stirewalt lived in, which was generally unfriendly to female officers, let alone scientists. During her remarkable career, Dr. Stirewalt published numerous articles, including several landmark papers that have been cited over 170 times. She was world-renowned for the striking figures in her papers, including this electron micrograph of three schistosome cercariae (larvae, two of them marked with the letter “C”) crawling along the skin of a mouse ear, looking for a suitable entry site:

Screen Shot 2014-06-03 at 8.34.39 PM.png

From Stirewalt and Dorsey, Exp Parasitol, 1974

Dr. Stirewalt also taught and mentored many of parasitology’s recent and current leaders, including Fred Lewis of BRI and Dan Colley from the University of Georgia. Dr. Stirewalt, with her husband Dr. David R. Lincicome, established the Harley Jones VanCleave Professorship in Life Sciences at the University of Illinois as a bequeathment. I am deeply honored to be the first recipient of yet another endowment in Dr. Stirewalt’s name. It is also my privilege to express my appreciation to Commander Stirewalt for her service to our nation. Isaac Newton spoke truly: “If I have seen further it is by standing on the shoulders of giants”. Thanks to Dr. Stirewalt, I hope to see that much further.

Our Frenemy, Schistosoma haematobium

Helminths, parasitic worms, have co-evolved with us for millennia, and, given their ability to often live in relative equilibrium with their hosts, have even been called "old friends". These old friends, however, are exquisitely capable of manipulating host biology to allow them to survive and reproduce in an otherwise hostile environment (recently reviewed by Boyett and Hsieh):


The host environment can be unfriendly to parasites through immune responses, as well as more physiologic activities such as mucus production (to entrap parasites and facilitate their subsequent expulsion) and diarrhea (to likewise facilitate parasite expulsion). Interestingly, parasite expulsion benefits both the parasite and host, since it allows the parasite to complete the portion of its life cycle that exists outside the host.

A fascinating aspect of host-parasite interactions is the concept of "collateral damage", inadvertent host modulation by the parasite. For example, Schistosoma haematobium, one of our model organisms, causes bladder cancer through poorly understood mechanisms, but nonetheless it is highly unlikely that this parasite has evolved to kill off its host (and thus, itself) by causing lethal cancers. It is more probable that some of the pathways by which S. haematobium alters the bladder epithelium to enable egg expulsion into the urinary stream happen to sometimes lead to carcinogenesis. Conversely, the chronic host inflammatory responses to S. haematobium eggs lodged in the bladder wall may be equally or more important pro-oncogenic factors.

Another means by which S. haematobium modulates the human host is by skewing immune responses directed against the parasite. There has been a long-standing but ill-defined association between S. haematobium infection and increased susceptibility to bacterial uropathogen co-infection. Theories to explain this association have included detection bias, obstruction, and immunomodulation. Detection bias refers to the possibility that patients with S. haematobium infection happen to be incidentally diagnosed with bacterial co-infection due to more intensive testing of their urine. In this scenario, the association is not a true biological one. The obstruction theory of S. haematobium-bacterial uropathogen co-infection states that the urinary tract fibrosis caused by S. haematobium leads to obstruction and urinary stasis, factors known to promote bacterial urinary tract infection. Finally, immunomodulation refers to the accepted ability of schistosomes to polarize the immune responses of their human hosts. Specifically, schistosomes are established inducers of potent type 2 immunity, exemplified by cytokines such as interleukin-4 (IL-4). Type 2 immunity in this setting leads to granuloma formation, aggregates of immune cells around parasite eggs which both sequester the rest of the host from the highly pro-inflammatory eggs and parasite toxins, as well as mediate subsequent expulsion of eggs from the body.

We recently published a paper demonstrating that S. haematobium-induced IL-4 abrogates the activation of natural killer T cells that would otherwise effectively clear bacterial uropathogen co-infection (Hsieh, Fu, and Hsieh). In a sense, S. haematobium has evolved to become an "accidental saboteur", since chronic infection confers increased susceptibility to bacterial uropathogen co-infection, and yet this susceptibility does not grant any apparent benefits to the parasite.

Interestingly, co-infection is thought to potentially increase risk of bladder cancer, possibly via production of carcinogenic compounds such as nitrosamines. Given all of these effects of S. haematobium infection on the human host, this parasite is not an "old friend". At best it is an ancient "frenemy". Keep you friends close, your enemies closer, and your frenemies closest. More research on helminths will help us eradicate these major sources of human suffering through diagnostic, drug, and vaccine development.

Boyett, D., & Hsieh, M. (2014). Wormholes in Host Defense: How Helminths Manipulate Host Tissues to Survive and Reproduce PLoS Pathogens, 10 (4) DOI: 10.1371/journal.ppat.1004014

Hsieh, Y., Fu, C., & Hsieh, M. (2014). Helminth-Induced Interleukin-4 Abrogates Invariant Natural Killer T Cell Activation-Associated Clearance of Bacterial Infection Infection and Immunity, 82 (5), 2087-2097 DOI: 10.1128/IAI.01578-13

Will the Worm Turn on Mother's Day?

The old English phrase "tread on a worm and it will turn" has been interpreted to mean that even the humblest worm (or person) will resent being badly treated and eventually revolt. In Henry VI, part 2, Shakespeare wrote: "The smallest Worme will turne, being troden on." The poet Robert Browning, in Mr. Sludge the 'Medium', declared: "Tread on a worm, it turns, sir! If I turn, Your fault!"

What does this have to do with Mother's Day? A literal worm, Schistosoma haematobium, can be argued to ruin the lives of many mothers and potential mothers throughout large swaths of sub-Saharan Africa. S. haematobium infection affects 112 million people worldwide, and causes severe bleeding into the urine (hematuria), bladder cancer, and may increase HIV susceptibility when it triggers genital disease in girls and women, a form of infection known as female genital schistosomiasis (FGS). It is estimated that 1/3 to 2/3 of all girls and women with S. haematobium infection have FGS, as highlighted in this recent New York Times article. It is not a stretch to envision S. haematobium infection and FGS ruining the lives of mothers and potential mothers through at least three ways:


First, FGS, by virtue of its associated parasite-induced inflammation of the female genital tract, causes infertility. Coupled with chronic pelvic pain and bleeding, infertility is a devastating complication of FGS for women of child-bearing age. Second, FGS is strongly suspected of increasing girls' and women's risks of contracting HIV. The biologic basis of this increased risk is poorly understood, but may involve parasite-induced migration of potential HIV "target cells" (certain cells of the immune system) to the lining of the female genital tract. Indeed, our laboratory has recently demonstrated in a mouse model that this hypothesis may be correct. Third, S. haematobium infection, since it disproportionately affects children, ruins the lives of mothers who have to witness the effects of this horrible disease on their offspring. Besides increased risk of bladder cancer, infected individuals often develop hematuria (bloody urine) that can be so severe as to render them anemic. This anemia can lead to growth stunting and poor school performance, factors that perpetuate the cycle of poverty for future generations in communities endemic for S. haematobium.

However, hope is not lost. Through a combination of mass drug administration campaigns, public health measures, and research efforts by our group and workers such as Eyrun Kjetland, Jennifer Downs, Hermann Feldmeier, and many others, I am optimistic that the "worms that will turn" someday soon are the fortunes of people from schistosomiasis-endemic communities. When that happens, Mother's Day will be made that much more special.

Richardson, M., Fu, C., Pennington, L., Honeycutt, J., Odegaard, J., Hsieh, Y., Hammam, O., Conti, S., & Hsieh, M. (2014). A New Mouse Model for Female Genital Schistosomiasis PLoS Neglected Tropical Diseases, 8 (5) DOI: 10.1371/journal.pntd.0002825

Studying Mono-Infections Drives a Relative “Vacuum” in Microbiology Research: Does It Suck?

The paradigm of reductionist, mechanistic biology, in which individual molecules and pathways are dissected from other phenomena and painstakingly characterized, has overall been a boon to microbiology research. For understanding host-microbe interactions, this approach to hypothesis-based science typically entails studying the interactions between a single microbe or macroparasite and its host. The benefits of this experimental framework have been innumerable and include the development of Koch’s postulates, the recognition of HIV as the cause of AIDS, and the vaccine-facilitated elimination of smallpox.

However, in reality our bodies are overflowing “soup bowls” for a veritable soup of microbes and macroparasites, including multiple potential pathogens. It is estimated that the human microbiome, the collection of all commensal and pathogenic microbes in and on the human body, is comprised of over 100 trillion microbes [1,2]. The collections of bacteria, viruses, fungi, and parasites we harbor determine the biological states we refer to as health and disease. Despite being massively colonized by an enormous range and numbers of microbes and macroparasites, most of us remain healthy. This fact indicates that our bodies have negotiated truces with the human microbiota, and in many cases commensal microbes confer benefits to Homo sapiens. Commensal bacteria, or microbial “Old Friends”[3], assist with metabolism of bile acids and bile acid proteins, vitamin absorption and production, inhibition of pathogen overgrowth, and fermentation of dietary carbohydrates. It is only when our bodies fail to control commensal microbes or macroparasites, or unsuccessfully repel more conventional pathogens, that the biological process known as infection ensues.

From this perspective it’s apparent that co-infections, also known as bystander infections, can occur when there are tripartite interactions among the host and two or more microbes or macroparasites. Indeed, microbiome scientists such as Faust and coworkers are beginning to demonstrate that specific microbes co-localize to anatomic sites of the human body, suggesting the existence of ecological relationships that promote niche competition or mutual growth and survival [4]:


“Significant co-occurrence and co-exclusion relationships among the abundances of clades in the human microbiome. A global microbial interaction network capturing 1,949 associations among 452 clades at or above the order level in the human microbiome... Each node represents a bacterial order, summarizing one or more genus-level phylotypes and family-level taxonomic groups. These are colored by body site, and each edge represents a significant co-occurrence/co-exclusion relationship. Edge width is proportional to the significance of supporting evidence, and color indicates the sign of the association (red negative, green positive). Self-loops indicate associations among phylotypes within an order... A high degree of modularity is apparent within body areas (skin, urogenital tract, oral cavity, gut, and airways) and within individual body sites, with most communities forming distinct niches across which few microbial associations occur.” [4]

The human microbiome does not exist in a vacuum. It is modified by dietary and environmental contacts incurred by humans during day-to-day activities. For instance, the lack of ideal sanitation in many parts of the world leads to excessive human exposure to multiple pathogens and increases risks of co-infections that may exacerbate infectious sequelae. Increased recognition of the importance to understand co-infection biology is reflected in the literature. In 2012 my graduate school classmate John Wherry wrote (with Dr. Erietta Stelekati) a Cell Host and Microbe review article highlighting how parasites, bacteria, and viruses intermingle in human hosts to impact immune responses and pathogen transmission[5]. More recently, other immunologists have commented specifically on how helminths may alter host immunity directed towards bacterial co-infections[6].

Understanding helminth-based co-infections is particularly germane to urogenital schistosomiasis, chronic infection by Schistosoma haematobium worms. S. haematobium has infected approximately 112 million people worldwide, with the majority of disease burden based in sub-Saharan Africa. Urogenital schistosomiasis encompasses a horrifying breadth of sequelae, including anemia-inducing hematuria (blood urine), painful urination, hampered school and work performance, growth stunting, obstructive kidney failure, and heightened risk of developing bladder cancer. The lack of public health-related infrastructure in many of these African countries endemic for urogenital schistosomiasis almost certainly contributes to co-infections by other pathogens.

There are hints in the literature that a number of pathogens interact differently with S. haematobium-infected versus non-infected human hosts. These pathogens include Salmonella, Plasmodium (the etiologic agent of malaria), HIV, and bacterial uropathogens. Some studies have noted an association of chronic or recurring urinary tract infections caused by Salmonella, often associated with intermittent bacteremia in some patients with urogenital schistosomiasis[7]. The latter association suggests that Salmonella bacteriuria in this setting may actually be “spill over” of bacteremia into the urinary stream. Phil LoVerde demonstrated that Salmonella organisms reside in the schistosome tegument, where they are presumably sheltered from host defenses [8]. However, despite the likelihood that salmonellosis with concomitant urogenital schistosomiasis renders co-infected individuals more ill than mono-infected people, not much is known about Salmonella-S. haematobium co-infections beyond these observations.

Plasmodium, in contrast, may have an inverse association with urogenital schistosomiasis. There are many prior publications suggesting that urogenital schistosomiasis may modulate host immune responses against Plasmodium infection [9–13], including a recent report by Lemaitre et al. noting lower malaria parasite densities in children with light S. haematobium co-infections [14]. Unfortunately many publications on Plasmodium-S. haematobium co-infections have reported immune effects that are potentially contradictory, highlighting the need for more work in this area.

Another poorly understood S. haematobium co-infection is HIV. A large proportion of girls and women with S. haematobium infections have female genital schistosomiasis (FGS), in which parasite eggs deposited in the female reproductive tract (i.e., vagina, cervix, vulva, etc.) induce tissue lesions that some researchers believe to increase HIV risk [15–23]. Accordingly, there are high rates of HIV co-infection among girls and women with FGS. However, whether this is a causal relationship remains unestablished, and certainly any associated mechanisms remain an open question.

A final set of examples of S. haematobium bystander infection are urinary tract co-infections with bacterial uropathogens. Bacterial urinary tract co-infection may worsen the sequelae of urogenital schistosomiasis, including hematuria, dysuria, and possibly bladder cancer risk [24]. Several reports have indicated that S. haematobium-infected individuals, particularly children, may be more susceptible to bacterial urinary tract co-infection than non-infected individuals in schistosomiasis-endemic areas [25–27]. However, a number of studies have disputed a link between these two infections [28,29]. The lack of a reliable animal model for S. haematobium infection has made it difficult to establish a causal link between urogenital schistosomiasis and bacterial urinary tract co-infection.

More broadly, the dearth of good animal models for urogenital schistosomiasis has also hampered our understanding of S. haematobium co-infections, including Salmonella, malaria, and HIV. A long-term goal of my laboratory is to develop such models. Until the field achieves such breakthroughs, studying S. haematobium mono-infections will be our only means by which to understand urogenital schistosomiasis. These are artificial and unrealistic approaches to comprehending S. haematobium and other blood flukes. They will continue to suck (blood).

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2. Paustian T (2006) The normal flora of humans. In: Paustian T, editor. Microbiology and bacteriology: the world of microbes. Madison, WI: University of Wisconsin-Madison.
3. Rook GAW, Raison CL, Lowry CA (2014) Microbial “Old Friends”, immunoregulation and socio-economic status. Clin Exp Immunol. Available: Accessed 13 January 2014.
4. Faust K, Sathirapongsasuti JF, Izard J, Segata N, Gevers D, et al. (2012) Microbial co-occurrence relationships in the human microbiome. PLoS Comput Biol 8: e1002606. Available: Accessed 13 January 2014.
5. Stelekati E, Wherry EJ (2012) Chronic bystander infections and immunity to unrelated antigens. Cell Host Microbe 12: 458–469. Available: Accessed 10 December 2012.
6. Salgame P, Yap GS, Gause WC (2013) Effect of helminth-induced immunity on infections with microbial pathogens. Nat Immunol 14: 1118–1126. Available: Accessed 10 January 2014.
7. King CH (2001) Disease in schistosomiasis haematobia. In: Mahmoud AAF, editor. Schistosomiasis. Lond: Imperial College Press. p. 265.
8. LoVerde PT, Amento C, Higashi GI (1980) Parasite-parasite interaction of Salmonella typhimurium and Schistosoma. J Infect Dis 141: 177–185. Available: Accessed 19 January 2014.
9. Courtin D, Djilali-Saïah A, Milet J, Soulard V, Gaye O, et al. (2011) Schistosoma haematobium infection affects Plasmodium falciparum-specific IgG responses associated with protection against malaria. Parasite Immunol 33: 124–131. Available:
10. Diallo TO, Remoue F, Gaayeb L, Schacht A-M, Charrier N, et al. (2010) Schistosomiasis coinfection in children influences acquired immune response against Plasmodium falciparum malaria antigens. PLoS One 5: e12764. Available:about:blank.
11. Diallo TO, Remoue F, Schacht AM, Charrier N, Dompnier J-P, et al. (2004) Schistosomiasis co-infection in humans influences inflammatory markers in uncomplicated Plasmodium falciparum malaria. Parasite Immunol 26: 365–369. Available:
12. Lyke KE, Dabo A, Arama C, Daou M, Diarra I, et al. (2012) Reduced T regulatory cell response during acute Plasmodium falciparum infection in Malian children co-infected with Schistosoma haematobium. PLoS One 7: e31647. Available:
13. Lyke KE, Dabo A, Sangare L, Arama C, Daou M, et al. (2006) Effects of concomitant Schistosoma haematobium infection on the serum cytokine levels elicited by acute Plasmodium falciparum malaria infection in Malian children. Infect Immun 74: 5718–5724. Available:
14. Lemaitre M, Watier L, Briand V, Garcia A, Le Hesran JY, et al. (2013) Coinfection with Plasmodium falciparum and Schistosoma haematobium: Additional Evidence of the Protective Effect of Schistosomiasis on Malaria in Senegalese Children. Am J Trop Med Hyg. Available: Accessed 19 January 2014.
15. Kjetland EF, Leutscher PDC, Ndhlovu PD (2012) A review of female genital schistosomiasis. Trends Parasitol 28: 59–66. Available: Accessed 27 January 2012.
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20. Poggensee G, Kiwelu I, Weger V, Göppner D, Diedrich T, et al. (2000) Female genital schistosomiasis of the lower genital tract: prevalence and disease-associated morbidity in northern Tanzania. J Infect Dis 181: 1210–1213.
21. Ndeffo Mbah ML, Poolman EM, Drain PK, Coffee MP, van der Werf MJ, et al. (2013) HIV and Schistosoma haematobium prevalences correlate in sub-Saharan Africa. Trop Med Int Health 18: 1174–1179. Available: Accessed 15 January 2014.
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Reading PubMed Abstracts in the Dark

Within PubMed, users can configure literature searches of interest to be run automatically at regular intervals and have e-mail alerts sent when new publications are annotated in PubMed. As someone who studies Schistosoma haematobium, the parasitic worm that causes urogenital schistosomiasis, I naturally have an automatic search configured for “haematobium”. I have a terrible habit each morning, after my wake-up alarm goes off, of checking my iPhone for any e-mail alerts of new PubMed articles on S. haematobium. Typically my bedroom is still dark and my mind groggy when I do this. Imagine this, then, when I recently saw an e-mail alert that raised my eyebrows and woke me instantly.

The e-mail alert contained the abstract for an in press Vaccine article entitled “Cross-species protection: Schistosoma mansoni Sm-p80 vaccine confers protection against Schistosoma haematobium in hamsters and baboons”. This abstract caught my attention for a number of reasons. First, although I am not currently engaged in schistosome vaccine research, I would love to be so. Second, I am keenly interested in the potential applications and limitations of various animal models of urogenital schistosomiasis. Despite hamsters being suitable hosts for S. haematobium infection, they tend to develop hepatoenteric schistosomiasis, rather than urogenital disease like S. haematobium-infected humans. This greatly limits the value of hamsters for urogenital schistosomiasis research.

Indeed, the authors of this Vaccine article noted no urogenital pathology in any of their 7 vehicle- and 10 vaccine-treated hamsters, all of which had been infected with S. haematobium. Remarkably, this was true even after 28 weeks of infection. As the authors stated, “in this study no eggs were detected in the urinary bladder of hamsters either in the control or the experimental group. This drawback limits the suitability of hamsters as a model to study S. haematobium-associated pathogenesis to the fullest.” The authors then go on to note that “the lack of an experimentally tractable small animal model has significantly limited our knowledge of vaccine efficacy and mechanistic aspects related to the urogenital schistosomiasis pathogen, S. haematobium”. This statement, which echoes my sentiments exactly, is followed by a citation of our 2012 PLOS Pathogens paper describing the first tractable animal (mouse) model of S. haematobium egg-induced bladder pathology. Like hamsters, mice that are naturally infected through the skin with S. haematobium cercariae, the larval stage infective for humans, develop hepatoenteric rather than urogenital disease. In our PLOS Pathogens paper we bypassed this problematic life cycle by directly microinjecting S. haematobium eggs into the mouse bladder wall, thereby delivering the parasite life stage of interest into the host tissues of interest.

The authors of the Vaccine paper remarked that “even though statistically significant data were obtained from the hamster model on prophylactic efficacy, the absence of eggs in the urinary bladder indicated a better model was needed and led us to develop and optimize a S. haematobium model in baboons”. I applaud the authors for their determination to develop and test their vaccine in a higher fidelity experimental model of urogenital schistosomiasis. It has long been known that baboons are suitable hosts for S. haematobium infection, but non-human primate studies, including those using baboons, suffer from a lack of species-specific reagents, logistical difficulties (due to costs and housing needs), and are ethically contentious. Accordingly, the authors were only able to test a total of four baboons – 2 receiving vehicle injections, and 2 receiving the candidate vaccine. Fortunately the authors were able to obtain favorable data on egg counts in the bladder and urine of these baboons, but their findings are statistically limited by the small sample size.

One of the authors’ interesting findings is that the candidate vaccine seemed to induce gamma-interferon and IL-17-secreting peripheral blood mononuclear cells:


This suggests that the vaccine induced antigen-specific cytokine secretion. Overall I was thrilled by this paper and I hope the vaccine succeeds. However, the manuscript perfectly highlighted some major shortcomings of my group’s work and the urogenital schistosomiasis research community more broadly. In short, we lack a tractable animal model of reliable, worm-based oviposition in host pelvic organs. Although my lab’s PLOS Pathogens paper was a contribution to the field, ultimately an egg-based mouse model of urogenital schistosomiasis is merely that. The vast majority of candidate diagnostics, drugs, and vaccines for urogenital schistosomiasis target adult S. haematobium worm-derived molecules. Baboons can be used for translational urogenital schistosomiasis research, but in the final analysis they are experimentally unwieldy. What we really need, and what my group continues to strive for, is a mouse model of worm-based egg laying in pelvic organs. The field needs a clever and reliable means to coax S. haematobium worms to lay eggs in the pelvic rather than digestive organs of the mouse. Success in this regard would open up urogenital schistosomiasis to high throughput diagnostic, drug, and vaccine testing.

I’m optimistic that we will eventually develop such a model. In the meantime, I’ll keep rolling over each morning and checking my iPhone for the latest updates.

Amazon Drones, the Terminator, and....Mass Drug Administration

Jeff Bezos, the CEO of, has recently been promoting the concept of a network of airborne drones that would enable rapid delivery of goods to otherwise difficult-to-access regions of the world: Not soon afterwards, Google completed its acquisition of Boston Dynamics, a robotics company that has designed a number of military-funded, walking and galloping robots that are incredibly anthropomorphic:

Some have speculated that Google’s purchase of Boston Dynamics may have been in part motivated by Bezos’ talk of a fleet of delivery drones. Specifically, Google may have plans to develop an array of walking/running robotic couriers to rival Amazon’s army of drones, if the latter possibility comes to fruition.

I am normally very pro-technology, but I admit that this video of Boston Dynamics’ Wildcat and Big Dog robots really creeped me out: and In short, these remarkably animalistic robots lies squarely in my uncanny valley. As described by Professor Masahiro Mori, “as the appearance of a robot is made more human, a human observer's emotional response to the robot will become increasingly positive and empathic, until a point is reached beyond which the response quickly becomes that of strong revulsion. However, as the robot's appearance continues to become less distinguishable from that of a human being, the emotional response becomes positive once again and approaches human-to-human empathy levels...This area of repulsive response aroused by a robot with appearance and motion between a "barely human" and "fully human" entity is called the uncanny valley.”

I am not alone in the uncanny valley. Numerous Internet outlets (such as Android Spin, see above) have made similar observations, evoking Skynet, the fictional corporation in the Terminator movies responsible for creating the artificial intelligence that brings about the conquest of humanity through mechanized animals and soldiers (including the movies’ titular Terminator robots).
A terminator robot with half of its underlying "face" exposed

I’m sure that Amazon and Google have the best of intentions, and in all likelihood these specific technologies will not be weaponized. The drones and robots showcased by Amazon and Boston Dynamics seem too fragile to accommodate military equipment.

After this realization, I began to wonder whether these technological advances could be used in mass drug administration (MDA) campaigns to treat helminth-infected individuals. Some of the greatest challenges in MDA efforts are the delivery of drugs to remote areas endemic for the helminth diseases in question. Due to a lack of transportation infrastructure (i.e., roads), many of these regions are inaccessible by anything other than bush aircraft and off-road ground vehicles. The required vehicles, drivers, medical staff, petrol , and supplies are considerable investments. In contrast, mass-produced drones and/or walking robots could be loaded with parcels of drugs and widely deployed from centralized locations. Depending on the particulars of the drones and robots, the cost savings could be considerable.

There may also be a role for drones and robots in disease risk mapping of helminth-endemic areas. Flying drones could cover vast swaths of territory and capture relevant climate and geographic data. Ground-based robots may be able to accomplish similar tasks, albeit likely at a slower rate, but could also sample water and soil for the presence of helminths and their intermediate hosts.

A number of potential issues with these technological approaches are foreseeable. The safety of these drones and robots would be a paramount concern. Any accidents involving humans, even minor, could trigger significant suspicion and doubt among the very populations that would benefit from MDA efforts. Moreover, the environmental impact of deploying these technologies, especially if they are noisy or rely on fossil fuels or heavy metals (i.e., lithium-based batteries), could be significant. Finally, target populations for MDA campaigns would need to actively participate in the receipt of drugs from drones and robots, let alone accept these foreign and potentially invasive technologies in their sovereign lands. These considerations may require major outreach initiatives that are culturally sensitive.

Despite these potential problems, I am optimistic that robots may have a role in MDA campaigns and geospatial mapping of helminth-endemic regions. Given that, to date, only about 10% of people with schistosomiasis have received anthelminthic therapy (, there is a desperate need for innovative approaches to MDA and helminth control efforts in general. So, perhaps we should indeed bring on the galloping robots and see whether they can help be the “Terminator” for neglected tropical diseases.

Angel Island

Helminths, parasitic worms that infect humans, sometimes seem distant in the idyllic Bay Area. However, San Francisco Bay’s Angel Island, once the immigration station for the West Coast, was open until 1940, and hookworm infections among hopeful immigrants were often used as a basis for deportation. One Chinese detainee at Angel Island wrote: “The savage doctors examine for hookworms. I could not go ashore because fate was not kind. Why should a young man take his life so lightly? To whom should I cry out for redress of these terrible wrongs?”


Fortunately hookworm and other helminth infections are now exceedingly rare in the United States. We hope that through helminth research we can contribute to eradicating helminth infections worldwide. Freedom and individual rights are the core of the evolving experiment we call America. The human right to be healthy is fundamental and we seek to facilitate the universal realization of this right through science.

Lasers and Time-Traveling Schistosomes in Space

I had the recent privilege of reading a very interesting paper in press by Chuah et al. in the Journal of Leukocyte Biology. The core technique of the publication is laser capture microdissection (LCM), which combines microscopy with the isolation and analysis of cells of interest:

Demonstration of liver granuloma section before (panel A) and after (panel G) laser capture microdissection of regions of interest.

The paper describes, for the first time, gene expression within various zones of liver granulomata induced by Schistosoma japonicum egg deposition. S. japonicum, one of two major parasitic worm species which cause human liver and intestinal schistosomiasis, is the cousin of Schistosoma haematobium, the etiologic agent of urogenital schistosomiasis.

Like all schistosome worms, S. japonicum worm eggs induce the formation of granulomata, dense collections of leukocytes, fibroblasts, and scar tissue. These features of schistosome egg-induced pathology were characterized many decades ago. However, a comprehensive analysis of the transcriptome in this setting, particularly with regards to how it relates temporally and spatially to different regions of egg granulomata, has until now never been undertaken.

Using LCM combined with microarrays, the authors demonstrated that different zones of liver granulomata tended to exhibit differential gene expression that segregated along specific functional pathways, including those involving neutrophils and fibrosis. Indeed, Chuah et al. bolster their LCM-derived neutrophil findings by demonstrating the presence of neutrophil extracellular traps (NETs) in S. japonicum but not Schistosoma mansoni liver granulomata. This confirms prior observations that S. japonicum liver granulomata tend to feature larger numbers of neutrophils than granulomata caused in the liver and bladder by S. mansoni and S. haematobium eggs, respectively. These findings point to tissue- and schistosome species-specific aspects of granuloma biology, an area of inquiry near and dear to our research group’s collective heart.

A better understanding of how various schistosomal granulomata form could reveal new therapeutic approaches for the unfortunate people who develop liver or kidney failure due to severe schistosomiasis. Although schistosomes currently can’t travel through time (or outer space – yet!), if they could, we’re certain that we could ask them why they exhibit tissue tropism. In the meantime, we’ll have to rely on tools like LCM with literal laser-like precision.

A Mother's Day for All

This Mother’s Day leads me to not only reflect on the fortunes of my own family, but also the misfortunes of other mothers. Urogenital schistosomiasis, chronic infection with Schistosoma haematobium worms, has long been suspected to affect the offspring of infected mothers. Earlier this year Fairley et al. reported an astounding 30.6% rate of S. haematobium infection among Kenyan mothers from the Kwale district, and a higher than expected rate of low birth weight offspring. Many of these mothers suffered from polyparasitism due to other infections such as malaria and soil-transmitted helminths, making it difficult to tease out the causal contribution, if any, of maternal urogenital schistosomiasis to low birth weight infants. Potential mechanisms by which urogenital schistosomiasis may lead to poor pregnancy outcomes include induction of anemia and/or chronic inflammation.


Another suspected but poorly understood association is the link between maternal urogenital schistosomiasis and priming of the fetal immune system by S. haematobium antigens that cross the placenta (Seydel et al.). Given the extraordinary ability of schistosomes to immunomodulate their hosts, it is possible that in utero exposure to S. haematobium products may affect not only postnatal immune responses to urogenital schistosomiasis, but perhaps risks of allergy and resistance to non-schistosome infections. However, definitive proof of such effects of S. haematobium on the human fetus remains to be established.

Thus, on this Mother’s Day, I call for renewed efforts to reduce the burden of urogenital schistosomiasis on the next generation, the very people who are the best hope for eradication of this disease in endemic areas.

Fairley, J., Bisanzio, D., King, C., Kitron, U., Mungai, P., Muchiri, E., King, C., & Malhotra, I. (2012). Birthweight in Offspring of Mothers with High Prevalence of Helminth and Malaria Infection in Coastal Kenya American Journal of Tropical Medicine and Hygiene, 88 (1), 48-53 DOI: 10.4269/ajtmh.2012.12-0371
Seydel LS, Petelski A, van Dam GJ, van der Kleij D, Kruize-Hoeksma YC, Luty AJ, Yazdanbakhsh M, & Kremsner PG (2012). Association of in utero sensitization to Schistosoma haematobium with enhanced cord blood IgE and increased frequencies of CD5- B cells in African newborns. The American journal of tropical medicine and hygiene, 86 (4), 613-9 PMID: 22492145

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