Source: Contaminated water and raw vegetables. Giardia parasites are microscopic protozoans that infect the intestines of several kinds of vertebrate animals. Distributed worldwide, Giardia occurs most commonly in areas with poor sanitation, affecting nearly 2% of adults in developed countries. Infections cause acute abdominal distress and chronic diarrhoea, with an infected person shedding 1-10 billion cysts daily. New infections occur from ingesting cysts in contaminated food or water.
Mode of Transmission: Undercooked infected beef and pork. Beef and pork tapeworms Taenia saginata and Taenia solium are impressively long parasites that can be contracted from eating undercooked red meat. When transmitted through ingested meat, larval tapeworms mature in the digestive system and live out their lives in the intestine, causing surprisingly few symptoms in their human hosts. When transmitted through food contaminated with infected human faeces however, pork tapeworms can cause cysticercosis, a potentially fatal condition.
Mode of Transmission: Infected raw or undercooked marine fish or squid. Anisakis, or herring worms, comprise a genus of parasitic nematodes that infect fish, crabs, and squid, as well as the marine mammals (and humans) that eat them. The parasites are prevalent in Japan, but have become more common globally due to the growing popularity of sushi. Some have reported experiencing tingling sensations after eating raw or undercooked fish or squid—caused by the parasite moving through the mouth and throat. A lucky few have been able to pull the worm out and prevent infection.
Mode of Transmission: Unwashed water plants such as watercress. The sheep liver fluke is a common parasitic trematode found around the globe, particularly in areas where sheep and cattle are raised. Human infections can occur from eating uncooked water plants, such as watercress, that contain resting cysts of the parasite. Once ingested, the developing flukes burrow out of the intestine and make their way to liver, where they feast on liver tissue and mature in the bile ducts.
Mode of Transmission: Raw or undercooked infected freshwater fish. The fish tapeworm is one of the largest human parasites—averaging 10m in length. This massive cestode travels up the food chain through freshwater fish, eventually infecting terrestrial carnivores including humans. Infections can last decades and most are asymptomatic, meaning many people carrying the tapeworm are unaware that they have a parasitic passenger.
Mode of Transmission: Unwashed fruits and vegetables. Also known as the Giant Roundworm, this common parasitic nematode is the largest intestinal roundworm that infects humans. Distributed worldwide, female Ascaris can produce up to 2000 eggs per day, which are passed in human faeces. Infection often occurs from eating unwashed produce that has been fertilized with “night soil,” or human waste—a common practice in parts of the developing world.
Mode of Transmission: Undercooked contaminated meat, especially pork, lamb and venison, and any contamination with cat faeces—often from unwashed fresh produce. Despite what many dog owners may think, domestic cats aren’t parasites. However, they are the primary source of one of the world’s most common parasitic protozoans, which is thought to infect more than 30% of the human population. Infections of healthy adults are rarely symptomatic, but can pose a serious health risk to developing foetuses and immunocompromised individuals. Among the parasite’s creepier attributes is its ability to alter the behaviour of rats, its typical host, to make them easier prey, and it may even cause slight personality changes in infected humans.
Who doesn’t love eating? Mealtimes provide us with the chance to relax, catch up with friends and savour some of our favourite flavours. Unfortunately, mealtimes are also a horrifying opportunity to pick up an array of common human parasites—looking to turn your body into their host and home. Munch with caution; these seven human parasites could be lurking in your lunch.