A parasite that infects the human brain, subtly changing its personality and social behavior, and capable of passing from mother to infect an infant in utero? That is the essence of a body horror, but this little rascal isn’t fiction. And it gets better: this parasite is considered to be one of the most successful parasites in the world due to its widespread, global distribution as well as its capacity to infect nearly every type of body tissue in all warm-blooded vertebrates (a). Schedule a phone conference with Spielberg and Cruise ASAP, guys, we’ve got the next sci-fi-action blockbuster on our hands (brains?). We’re looking at the ubiquitous protozoa Toxoplasma gondii and research on its capacity to modulate human personality and behavior.
In the early 20th century, the Rockefeller Foundation embarked upon a massive public-health campaign that radically changed the economic landscape of the Southeastern United States. A parasite, the hookworm Necator americanus, not only had been leeching Southerners of their blood and good health but also of their agricultural productivity and wealth.
It’s getting to be summer time in the Northern Hemisphere and I’m starting to see more creepy-crawlies outside, inside and attacking my personal space. Spiders, mosquitoes and cockroaches are becoming an increasingly common, unpleasant sight. Finding these beasties in random corners of my house and ruthlessly killing them had me thinking about the human-insect relationship, in particular the special one we have with ectoparasites. Ectoparasites depend upon mammals for their survival but there are several that rely on humans specifically and have co-evolved over hundreds of years to inhabit our bodies. Examples include the sucking lice (body, head and crab), bed bugs, fleas and mites.
This is more of a light-hearted post than usual. I have a few favorite songs and, of course, they’re about infectious diseases. I’m a microbiologist, what’re you gonna do? Case closed, moving on. I’ve been on the hunt for songs specifically about microbes and tracked down some real treasures.
We usually associate cancer with environmental determinants, such as gamma ray or bisphenol A exposure, but two parasitic flukes that have been implicated in more than two-thirds of cases of a rare liver cancer in Southeast Asia and parts of East Asia may change how we think about carcinogens. The most fascinating aspect of these two parasites, Opisthorchis viverrini and Clonorchis senensis, is that human infection is directly associated with a culturally-specific method of cooking food, or in this case, not cooking it.
I love this picture of a female lone start tick and her enormous egg mass not just because of the striking imagery, but because it confronts the viewer with a major difficulty commonly encountered in tick and tick-borne disease control – reducing the dangers of a relatively small but fast reproducing species capable of stealthy and lethal infection. Many public health and entomology initiatives focus on mosquitoes but I’ve always found ticks to be the more fascinating arthropod. They’ve got that essential “creepy” factor but they’re also prodigious reproducers and can transmit a slew of truly nasty diseases. Renewed interest for public health practitioners in these creatures stems from the growing problem of habitat change that is resulting in increasing numbers of habitats and climates well-suited to ticks.
A recent article detailing the sad situation of a transplant patient contracting AIDS from the kidney of a living donor, despite negative tests 11 weeks prior to the surgery, had me thinking about transfusions, the blood supply and the spread of infectious disease (a). Unsavory musings, yes, but there’s one particularly exotic disease and a rather sensitive public health situation that I was thinking about that I wanted to explore in this post.
Chagas disease (Trypanosoma cruzi), otherwise known as American trypanosomiasis, is a protozoan parasite endemic to Central and South America. The CDC estimates that a staggering 16-18 million people are infected with T. cruzi in Latin America, mostly in rural locales, with another 25,000 to 100,000 infected immigrants in the United States (b). Typically, the disease is transmitted by triatomine insects that blood-feed on a humans. Their infective feces often enter the bite wound, oral or nasal mucosa, or conjunctivas and transmit the flagellate parasite.
The disease has two specific phases. The acute phase is usually a mild febrile infection lasting anywhere from weeks to months. Following this acute phase, researchers believe there is life-long infection with the parasites hiding in the blood and organs of the infected person. Years or decades later, 10 to 30% of those cases can progress to chronic Chagas disease.
The clinical manifestations of chronic Chagas disease are ugly business, characterized by enlargement of the heart and digestive tract, “megaesophagus” and “megacolon” being two common presentations of digestive tract pathologies. Electrocardiographic abnormalities, myocardial lesions, constipation and dysphagia (difficult or painful swallowing) are just a few of the symptoms resulting from infection (c)(d). There is no vaccine for primary infection and no effective drug therapy available for the chronic stages.
The disease may also be spread by congenital infection, oral infection through contaminated fruit, and, as you can guess, by blood transfusion and organ transplantation. Platelet transfusions and renal transplants in particular seem to be problematic, suggesting an as yet unknown immunological component of T. cruzi infection; the liver, pancreas and heart have also been implicated in so-called “allographic transmission” resulting from organ transplantation (b)(h)(i).
Prior to the successful Southern Cone Initiative that tackled both the eradication of the triatomine bug as well as initiating large-scale blood-screening efforts in Latin America in 1991, blood transfusion-transmitted Chagas was a critical public health problem with infectivity rates ranging from 13 to 49% (f). As the issue started drawing attention in public health sectors in the United States, the American Red Cross (ARC) conducted a study and observed evidence of increasing prevalence of the disease in blood donors in Southern California throughout the early 1990s (g). This increase was attributed not only to changes in donor and population demographics but also as a result of recruitment efforts directed towards minority donors in Los Angeles at the time (h).
As late as the year 2007, no policies were in place for compulsory blood-bank screening for Chagas in the United States (b). Upon the release of the first F.D.A. licensed serological test using a parasite lysate ELISA for T. cruzi blood screening in January of 2007, the ARC and Blood Systems Laboratories conducted a study using the test on 14 million blood donors over 16 months. They detected over 500 confirmed Chagas-infected donations (28% of the sample), with the majority of those cases from California and Florida (g).
In terms of actual transmission events in North America, the only reliable numbers I was able to hunt down in the literature were five blood transfusion-transmission and five organ transplant-transmission cases since 1993, an extraordinarily low number (g). Indeed, researchers believe that number to be too low to serve as any true indication of this phenomenon in the US (g)(d).
Of course, this Chagas story has traces of the HIV-infected blood transfusion panic in the late 1980s. Regrettably, there’s even a minority group entangled in the plot-line; evidence strongly suggests that Chagas-infected blood and organs originate from seropositive immigrants from T. cruzi endemic Latin American countries. Luckily, research has consistently indicated that blood donor recipients from seropositive donors are rarely infected with Chagas disease (f)(g)(h). Compared to the 93% of recipients that contract HIV after an infected blood donation, only 13% of recipients become infected after blood transfusion owing to factors such as parasite strain and levels of donor parasitemia (g). Recipients of platelets appear to be most at risk, most likely due to their immunocompromised state (f). The risk for allographic transmission seems to be much greater, determined to be as high as 35% for recipients of infected kidneys (i).
The past several decades have seen the proliferation of blood-bank screening for blood-borne diseases such as HIV-1 and HIV-2, hepatitis B and C, HTLV-I and -II and the etiological agent of syphilis, Treponema pallidum. The HIV epidemic really dragged this issue kicking and screaming to the forefront and since then there have been fantastic strides in implementing screening efforts as well as increasing public awareness of these issues. Chagas disease is the latest infectious disease agent to enter the equation and public health officials have put several tests in place to screen both blood and organ donors for antibodies to previous or ongoing Chagas infection. Of course, blood transfusions and organ transplants are never risk-free but knowing what blood-borne pathogens are lurking out there is the biggest part of the battle.
(a) “Transplant patient got AIDS from new kidney; living donor was infected” Arizona Daily Star. 17 Mar. 2011. Web: 20 Mar. 2011
(b) Centers for Disease Control and Prevention (CDC) (2002) Chagas disease after organ transplantation – United States, 2001. MMWR Morb Mortal Wkly Rep. 15:51(10):210-2
(c) Despommier, D, Gwadz RW, Hotez PJ & Knirsch CA. Parasitic Diseases. 5th ed. New York: Apple Trees Production, LLC. 2006
(d) Dias E, Laranja FS, Miranda A & Nobrega G. (1956) Chagas’ Disease: A Clinical, Epidemiologic, and Pathologic Study. Circulation. 14(6):1035-60
(e) Busch MP, Kleinman SH & Nemo GJ. (2003) Current and Emerging Infectious Risks of Blood Transfusions JAMA. 289(8):959-62.
(f) Leiby DA, Read EJ, Lenes BA, Yund AJ, Stumpf RJ, Kirchhoff LV & Dodd RY. (1997) Seroepidemiology of Trypanosoma cruzi, Etiologic Agent of Chagas’ Disease, in US Blood Donors. J Infect Dis. 176(4):1047-52.
(g) Bern C, Montgomery SP, Katz L, Caglioti S & Stramer SL. (2008) Chagas disease and the US blood supply. Curr Opin Infect Dis. 21(5):476-82.
(h) Leiby DA, Herron RM Jr, Read EJ, Lenes BA & Stumpf RJ. (2002) Trypanosoma cruzi in Los Angeles and Miami blood donors: impact of evolving donor demographics on seroprevalence and implications for transfusion transmission. Transfusion. 42(5):549-55.
(i )Kun H, Moore A, Mascola L, Steurer F, Lawrence G, Kubak B, Radhakrishna S, Leiby D, Herron R, Mone T, Hunter R, Kuehnert M; Chagas Disease in Transplant Recipients Investigation Team (2009) Transmission of Trypanosoma cruzi by heart transplantation. Clin Infect Dis. 48(11):1534-40
Centers for Disease Control and Prevention (CDC) (2002). Chagas disease after organ transplantation–United States, 2001. MMWR. Morbidity and mortality weekly report, 51 (10), 210-2 PMID: 11922190