We don’t normally think of human roundworm infection as a problem in the modern world, but it is. Studies have found that in soil samples from playgrounds approximately 20% of samples were contaminated with roundworm eggs. This would be partially due to animals being exercised in parks and playground areas. Most human roundworm infections occur in people under 20 years with children being at highest risk.
Most people have very mild or no symptoms, but it all depends on how many worm eggs someone is exposed to. These species of roundworms employ a full body migration through their host as part of their development and symptoms in the human host result as part of this migration.
Variable symptoms occur as roundworm larvae make their way through the human body. Fever, abdominal discomfort, swollen lymph nodes, cough, headache, and interrupted sleep are the main ailments.
When roundworm larvae migrate in their natural host (dog or cat), they are able to recognise molecular signposts directing them so that they end up in the GI tract at the end of their journey. In the human body the signposts are all wrong and the larvae tend to get lost. For unknown reasons, roundworm larvae are frequently misdirected to the human eye where they die and generate tremendous inflammation. Usually, one eye and one single larva are involved. Vision loss occurs over days to weeks and permanent blindness can result. Damage to the eye is permanent. Children aged 7 to 8 are typically infected. In the U.S. there are approximately 1,000 cases of ocular larva migration seen annually, with about 700 of these cases resulting in permanent blindness.
Human roundworm infection can be caused by accidentally consuming dirt that has been contaminated with roundworm eggs. The eggs require at least a month in soil to develop to an infective stage. Dogs are not the only culprits. Outdoor and feral cats will deposit their faeces in children’s sandpits, so it is important that these are covered when not in use to reduce contamination. It is possible to become infected by eating undercooked meals in the same way that dogs and cats become infected through their prey. You may also become infected by kissing a pet or patting their fur and then touching your mouth. The most significant thing you can do to prevent human infection is to wash your hands before cooking and eating and teach your children to do the same.
The best practice for animal care is to continue to provide heartworm, intestinal worming, and flea control on a monthly basis.
