World Health Organization Estimates of the Global and Regional Disease Burden of 11 Foodborne Parasitic Diseases, 2010: A Data Synthesis

Abstract

Background

Foodborne diseases are globally important, resulting in considerable morbidity and mortality. Parasitic diseases often result in high burdens of disease in low and middle income countries and are frequently transmitted to humans via contaminated food. This study presents the first estimates of the global and regional human disease burden of 10 helminth diseases and toxoplasmosis that may be attributed to contaminated food.

Methods and Findings

Data were abstracted from 16 systematic reviews or similar studies published between 2010 and 2015; from 5 disease data bases accessed in 2015; and from 79 reports, 73 of which have been published since 2000, 4 published between 1995 and 2000 and 2 published in 1986 and 1981. These included reports from national surveillance systems, journal articles, and national estimates of foodborne diseases. These data were used to estimate the number of infections, sequelae, deaths, and Disability Adjusted Life Years (DALYs), by age and region for 2010. These parasitic diseases, resulted in 48.4 million cases (95% Uncertainty intervals [UI] of 43.4–79.0 million) and 59,724 (95% UI 48,017–83,616) deaths annually resulting in 8.78 million (95% UI 7.62–12.51 million) DALYs. We estimated that 48% (95% UI 38%-56%) of cases of these parasitic diseases were foodborne, resulting in 76% (95% UI 65%-81%) of the DALYs attributable to these diseases. Overall, foodborne parasitic disease, excluding enteric protozoa, caused an estimated 23.2 million (95% UI 18.2–38.1 million) cases and 45,927 (95% UI 34,763–59,933) deaths annually resulting in an estimated 6.64 million (95% UI 5.61–8.41 million) DALYs. Foodborne Ascaris infection (12.3 million cases, 95% UI 8.29–22.0 million) and foodborne toxoplasmosis (10.3 million cases, 95% UI 7.40–14.9 million) were the most common foodborne parasitic diseases. Human cysticercosis with 2.78 million DALYs (95% UI 2.14–3.61 million), foodborne trematodosis with 2.02 million DALYs (95% UI 1.65–2.48 million) and foodborne toxoplasmosis with 825,000 DALYs (95% UI 561,000–1.26 million) resulted in the highest burdens in terms of DALYs, mainly due to years lived with disability. Foodborne enteric protozoa, reported elsewhere, resulted in an additional 67.2 million illnesses or 492,000 DALYs. Major limitations of our study include often substantial data gaps that had to be filled by imputation and suffer from the uncertainties that surround such models. Due to resource limitations it was also not possible to consider all potentially foodborne parasites (for example Trypanosoma cruzi).

Conclusions

Parasites are frequently transmitted to humans through contaminated food. These estimates represent an important step forward in understanding the impact of foodborne diseases globally and regionally. The disease burden due to most foodborne parasites is highly focal and results in significant morbidity and mortality among vulnerable populations.

Abstract

In this data synthesis, Paul Robert Torgerson and colleagues estimate the global and regional disease burden of 11 foodborne parasitic diseases.

Editors' Summary

Background

Foodborne diseases cause a large burden of illness (morbidity) and death (mortality), worldwide. More than 200 diseases can be transmitted to people through the ingestion of food contaminated by microorganisms (viruses, bacteria, and parasites) or with chemicals. Food can become contaminated on the farms where crops and animals are raised, in food processing plants, and during food storage and preparation at home and in restaurants. Food contamination can be caused by pollution of water and soil by human and animal feces and by poor hygiene practices such as not washing one’s hands after using the toilet or before handling food. Many foodborne diseases present with gastrointestinal symptoms (stomach cramps, diarrhea and vomiting) but some also affect other parts of the body and some have serious sequelae (abnormal bodily conditions or diseases arising from a pre-existing disease). For example, the parasitic tapeworm Taenia solium (which is spread by eating undercooked pork) can cause cysticercosis, an infection of tissues by larval cysts that can result in seizures, stroke and death.

Why Was This Study Done?

National and international efforts to improve food safety need accurate information on foodborne infections so, in 2007, the World Health Organization (WHO) established the Foodborne Disease Burden Epidemiology Reference Group (FERG) to provide estimates of the global and regional burden of disease attributable to foodborne illnesses. Here, researchers involved in one of FERG’s constituent task forces—the Parasitic Diseases Task Force—combine information from many different sources (a data synthesis) to provide estimates of the regional and global disease burden of ten helminth diseases and toxoplasmosis attributable to contaminated food. Examples of helminths (parasitic worms) include roundworms ( Ascaris lumbricoides; heavy roundworm infections [ascariosis] can cause signs of malnutrition or even intestinal blockages), tapeworms and flukes (liver and lung flukes cause a condition known as trematodosis; frequently transmitted in undercooked fish crustacea or aquatic vegetables). Toxoplasmosis is caused by a parasite found in undercooked meat and in cat feces. If a woman becomes infected during pregnancy, she can pass the parasite onto her unborn child (congenital toxoplasmosis), thereby causing eye problems and sometimes developmental problems and seizures later in life.

What Did the Researchers Do and Find?

The researchers combined national estimates of foodborne diseases, and data from systematic reviews (studies that identify all the research on a topic using predefined criteria), national surveillance programs, and other sources to estimate the number of illnesses, sequelae, and deaths for ten helminth diseases and toxoplasmosis. They also estimated the number of disability adjusted life years (DALYs) globally and regionally for each disease. A DALY is the disease-related loss of one year of full health because of premature death or disability; DALYs provide a measure of the burden of a disease. Together, these diseases caused 48.4 million cases of illness, 59,724 deaths, and 8.78 million DALYs in 2010. The researchers estimated that 48% of these cases of parasitic diseases, resulting in 6.64 million DALYs, were transmitted by contaminated food. The commonest foodborne parasitic diseases were Ascaris infection and toxoplasmosis (12.3 million and 10.3 million cases, respectively). Foodborne cysticercosis, trematodosis and toxoplasmosis resulted in the highest disease burdens, and the largest burden of foodborne parasitic disease occurred in the Western Pacific and African regions.

What Do These Findings Mean?

The lack of reliable data on the diseases considered in this study for many regions of the world and the use of expert panels to estimate the proportion of each disease that is foodborne may limit the accuracy of these findings. Moreover, this study does not estimate the global burden of every potentially important foodborne parasitic disease. However, these findings, together with those on three foodborne enteric protozoa (single-celled parasites that infect the intestines) included in a related paper, indicate that parasites are frequently transmitted to people through contaminated food and that, although some parasites result in a low burden of disease, foodborne parasites result in significant illness and death that is often borne by relatively small populations in limited geographical areas. This information, together with other estimates on foodborne disease obtained by FERG, should facilitate the development and implementation of effective national and global food safety policies.

Additional Information

This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at http://dx.doi.org/10.1371/journal.pmed.1001920.

• A related PLOS Medicine Research Article by Kirk et al that includes data on foodborne enteric parasites is available

• The World Health Organization provides information about soil-transmitted helminths, foodborne diseases, food safety, and the estimation of the global burden of foodborne diseases (available in several languages); it also provides fact sheets on cysticercosis, trematodosis, and ascariasis

• The US Centers for Disease Control and Prevention (CDC) provides information about foodborne disease outbreaks in the US and elsewhere and information about food safety in the US; it also provides general information about soil-transmitted helminths; more detailed information about individual diseases caused by helminths and about toxoplasmosis can be found by visiting the CDC’s alphabetical index of parasites

• The UK National Health Service Choices website provides information about roundworm infections and tapeworm infections, and about food safety

• PARA-SITE, an electronic resource devoted to parasitology that is provided by the Australian Society of Parasitology, provides more information about the biology of helminth parasites