[Above: Human parasitic diseases. Clockwise from upper left: cutaneous leishmaniasis, ascariasis, lymphatic filariasis, malaria, African trypanosomiasis (sleeping sickness), Chagas disease (Romana’s sign), onchocerciasis (river blindness).]

The burden of parasitic disease is enormous. The Global Burden of Disease Studies of 2010 and 2013 provided estimates for all forms of mortality and disability experienced world wide. Death and morbidity caused by a variety of degenerative disease, accidents, mental illness, war, infectious disease, natural disasters, and much more were quantified and reported upon. A key concept in these studies is the term DALY, or Disability Adjusted Life Year. DALYs are roughly the sum of Years of Life Lost (YLL) due to premature mortality and Years Lost due to Disability (YLD) for people living with a health condition or its consequences. In other words, one DALY is one year of healthy life lost. The human population experienced a total of 2.5 billion DALYs in 2013, that’s a lot of suffering, but represents a significant reduction (~25%) since 1990. Below is a table listing DALYs, disease prevalence and annual mortality rates estimated for the most common human parasitic diseases. Click on the links to learn more about the various parasitic diseases.

Parasitic disease DALY (millions) Estimated cases in a year* Yearly death estimates
Malaria 65.5 198,000,000 584,000
Cryptosporidiosis 8.4 276,000,000 100,000
Leishmaniasis 4.3 10,000,000 51,600
Foodborne trematodiases 3.6 16,000,000 7000
Schistosomiasis 3.1 252,000,000 11,700
Hookworm 2.2 439,000,000 900
Amebiasis 2.2 297,600,000 55,000
Lymphatic filariasis 2.0 36,000,000 300
Ascariasis 1.3 819,000,000 900
Toxoplasmosis (congenital) 1.2 190,000
Trichuriasis 0.6 465,000,000 900
Onchocerciasis 0.5 30,000,000
African trypanosomiasis 0.4 37,000 9,100
Chagas Disease 0.3 5,700,000 10,300
Cysticercosis 0.3 1,400,000 1,200
Trichomoniasis 0.1 2,760,000
Sum for all Parasitic disease 96.0 2,848,687,000 832,900

With the exception malaria, most of the listed parasitic diseases are considered neglected, many of which affect the poorest in developing and third world countries. With ~1 in 6 people worldwide experiencing some form of parasitic disease, it is shocking to note that currently (2015) we have no licensed vaccine for any human parasitic pathogen. Drug discovery also lags behind. As DNDi notes, “Of the 1,556 new drugs approved between 1975 and 2004, only 21 (1.3%) were specifically developed for tropical diseases and tuberculosis, even though these diseases account for 11.4% of the global disease burden.”

With strong public health programs, political will, financial backing, proper sanitation, mass drug administration and insect control certain human parasitic diseases can be controlled and even eliminated. For example, in the US our mosquito abatement programs after World War II eliminated malaria from the country in 1951 (as a reference, in 1930 there were 123,000 cases of malaria in the US), and hookworm elimination programs in the early 20th century significantly reduced hookworm infections in the South. These efforts had profound effects on the local economy, health and well being. However, for a variety of reasons (political, financial, ecological, biological) it is difficult to control or eliminate certain parasitic pathogens from a region, hence there is need for new cost effective therapies for human parasitic disease. Part of what we are trying to do in the Jensen lab is to address this issue and find ways to better stimulate our immune system to combat human parasites.

Table above. *Represents the number of people with a disease in a given year, or disease prevalence. This is not the number of infections per year, as many of infections are chronic or prolonged conditions that occur over many years. Cases are usually symptomatic and can range in severity. “-” signifies that the death estimates are not known. Data is pulled from a variety of sources including the WHO; the Global Burden of Disease studies 2013; Pullan et al. Parasite & Vectors 2014; Brooker et al. Int. J. Parasitology 2011; Torgerson, Trends in Parasitology 2014.