For residents of temperate, developed countries, it may be difficult to imagine just how common helminth infections are in the human population. In fact, they are quite common and even occur frequently in the United States. Worldwide, approximately 807–1,221 million people are infected with Ascaris lumbricoides (perhaps one-sixth of the human population) and far more are infected if all nematode species are considered. Rates of infection are relatively high even in industrialized nations. Approximately 604–795 million people are infected with whipworm (Trichuris) worldwide (Trichuris can also infect dogs), and 576–740 million people are infected with hookworm (Necator americanus and Ancylostoma duodenale). Toxocara, a nematode parasite of dogs and cats, is also able to infect humans. It is widespread in the United States, with about 10,000 symptomatic cases annually. However, one study found 14% of the population (more than 40 million Americans) was seropositive, meaning they had been exposed to the parasite at one time. More than 200 million people have schistosomiasis worldwide. Most of the World Health Organization (WHO) neglected tropical diseases are helminths. In some cases, helminths may cause sub-clinical illnesses, meaning the symptoms are so mild that that they go unnoticed. In other cases, the effects may be more severe or chronic, leading to fluid accumulation and organ damage. With so many people affected, these parasites constitute a major global public health concern.
OpenStax Microbiology. https://openstax.org/