Parasitic and Other Infectious Diseases Affect America's Poor

America's poor citizens, numbering approximately 36 million, are preferentially affected by more than a dozen ignored infections—including those caused by parasitic worms (left). A review of these "neglected infections of poverty" is provided by Peter Hotez, MD, PhD, in this month's issue of PLoS Neglected Tropical Diseases.

The cited diseases, many of which are endemic to third-world nations, are not confined to America's recent immigrants, writes Hotez, but prominently affect native-born people. He concludes that individuals in geographic regions of poverty—such as Appalachia, the Mississippi Delta, the Cotton Belt, the US-Mexican border, and Native American tribal lands—are particularly vulnerable. Although Hotez estimates high rates of these infections among the nation's poor (and specifically, among the minority poor), he emphasizes that an important obstacle to their control is the absence of recent and reliable prevalence data.

Soil-Transmitted Helminthic Infections

Ascariasis: According to the most recent survey, which was way back in 1974 (Warren KS. Am J Trop Med Hyg. 1974;23:723-730), up to 4 million people (particulary children) in the American South may be infected with Ascaris lumbricoides, the largest and most common intestinal roundworm (above). 

Toxocariasis: Up to 30% of rural African American children, mostly in the South, were seropositive for Toxocara canis, or dog roundworm, during the 1970s and 1980s, writes Hotez; however, disease surveys since that time are lacking. He estimates that 1.3-2.8 million Americans are exposed or infected, with at-risk populations in America's inner cities, the South, and Appalachia. In poor urban areas of the United States, playgrounds and sandboxes are often contaminated with T. canis eggs.

Strongyloidiasis: Threadworm, or Strongyloid stercoralis, may infect as many as 100,000 people in the United States, particularly in Appalachia. Hotez also reports that there is a 25% prevalence rate of strongyloidiasis (and a 75% rate of infection with the Schistosoma water fluke) among Somali and Sudanese immigrants. Consequently the CDC recommends presumptive treatment with antihelminthics in these groups. 

Protozoan Infections

Chagas disease: Infection with the flagellate protozoa Trypanosoma cruzi is traditionally an insect-borne illness, although the potentially fatal disease (for which there is no reliable treatment) may be transmitted through contaminated food and even by blood transfusion. Hotez cites the rise of domestic blood-sucking tratomines (or assassin bugs), which transmit the protozoa, and the 2007 report of human disease in post-Katrina New Orleans. Because of the high rate of infection among indigenous wildlife (eg, armadillos, opossums) in Louisiana and along the US-Mexican border, Hotez estimates the prevalence of Chagas disease in the United States at anywhere from 3000 to more than 1 million.

Amebiasis and leishmaniasis: Hotez reports that there are insufficient data to estimate the US prevalence of intestinal amebiasis, which is transmitted through food or water, and leishmaniasis, which is transmitted by the sand fly; however, he believes that poor populations along the US-Mexican border are especially at risk for these diseases. According to Wikipedia, US troops serving in the Middle East have experienced cutaneous leishmaniasis, or "Bagdad boil."

Bacterial Infections

Trench fever: Caused by gram-negative Bartonella quintana, trench fever (so-called because of its high prevalence among trench-living soldiers during World War I) is a louse-borne illness. Small outbreaks of trench fever have been documented among the homeless in Seattle and other urban areas since the 1990s; although the estimated US prevalence of the disease remains unknown.

Leptospirosis: A spirochetal infection of the urban poor, leptospirosis is transmitted through water contaminated by rat urine. Hotez reports that there are insufficient data to estimate the US prevalence of the infection, which can cause multisystem failure and DIC.  

Viral Infections

Dengue fever: From 110,000 to 200,000 new cases of this mosquito-borne illness occur annually in the United States, clustering along the US-Mexican border. Candidate vaccines for dengue fever are in development. 

Other poverty-level infections of concern include those caused by platyhelminths (cysticercosis, schistosomiasis, and echinococcus) and congentially transmitted diseases that preferentially affect poor American women (CMV, toxoplasmosis, syphilis). Although giardiasis is the most common parasitic infection in the United States, with an estimated prevalence of 2 million or more, Hotez writes that the disease does not appear to preferentially affect the poor.

He concludes, "Control of these neglected infections needs to be prioritzed...because it is both a highly cost-effective mechanism for lifting disadvantaged populations out of poverty and consistent with our shared American values of equity and equality." 

DIC = disseminated intravascular coagulopathy.

Gross-out photo of mass of Ascaris lumbricoides worms, held by CDC's Henry Bishop, from the CDC/James Gathany.