The aptly named Dioctophyma renale reaches maturity in the host’s kidneys. Also known as giant kidney worms, they are one of the largest nematodes capable of infecting humans-adult females grow to be over 100 cm long (they are also bright red and about 10 mm wide). Although they don’t feed on kidney tissue, they cause pressure necrosis (imagine a meter-long, centimeter wide worm living in your roughly computer mouse-sized kidney), turning the kidney into a non-functioning hollow shell. It has a cosmopolitan distribution and affects humans, several species of canids, horses and pigs, and uses annelids as intermediate hosts (fish can be paratenic hosts). Vertebrate hosts become infected by eating an infected intermediate or paratenic host or by drinking water in which they are swimming. Luckily, human infections are uncommon. On rare occasions, they become encysted in other organs (e.g. ovaries, uterus, urethra, mammary gland or subcutaneous tissue) or migrate through the digestive tract or abdominal cavity, making for an unpleasant finding during veterinary surgical procedures.
Contributed by Andrés Gómez.
Photo from this site.