When Globalization Brings Brain-Invading Worms

The parasite that causes rat lungworm disease is now endemic in the southeastern United States, and it’s expected to spread northward.

There is a long, grim history of infectious diseases crisscrossing the globe aboard giant ships.

Explorers looking to set up new colonies carried smallpox, measles, and other deadly viruses with them to distant lands. Even the vessels they used to get there contributed to the spread of disease. Infected ballast water from cargo ships traveling to South America, for example, has been blamed for introducing cholera there.

The rise of aviation exacerbated the global spread of disease, effectively shrinking the distance between any one place and the next. (Vaccines have been a major mitigating factor, but there are always emerging diseases, illnesses for which there are no vaccines, and unvaccinated people.) There are tens of thousands of commercial flights across the planet each day, each one carrying a unique stew of germs and vectors. Mosquitoes, which occasionally board and survive international flights, have likely been responsible for bringing malaria to new countries, according to the World Health Organization.

But global shipping still plays a substantial role in the spread of deadly diseases. Consider rat lungworm disease, a grave illness caused by a parasitic worm that invades the human brain. The roundworm that causes the disease, Angiostrongylus cantonensis, is now endemic in the United States. Like many diseases, it is carried by infected rats on container ships, as well as by intermediate hosts like slugs and snails.

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