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Many parasitic diseases can hide in the body for decades, but they can be lethal when they come out of hiding. By Carrie Arnold.

The headaches wouldn’t stop. For more than seven months, Teresa Tovar had suffered from excruciating headaches, and an ever-increasing number of physicians kept prescribing migraine medications. But none of the prescriptions provided the 39-year-old Tovar any relief.

Finally, on 29 December, after her headaches worsened and she had begun vomiting, Tovar got an appointment for a CT scan at the Smith Clinic, Houston’s safety net clinic for under-insured and uninsured people. When she showed up on 12 January, however, she fainted and was rushed to Ben Taub Hospital. There, she received her CT scan, which revealed a large cyst in her brain – the work of a parasitic disease called neurocysticercosis.

Tovar, who grew up in a small village near Matehuala in central Mexico, knew of others there who had suffered the condition but never suspected her headaches were caused by it. After all, she had left Mexico more than 20 years before, although she often returned to visit her mother and other relatives.

When Dr Rojelio Mejia questioned her about what she ate growing up, however, it became clear how Tovar had probably acquired the parasite. The parasite is a tapeworm (Taenia solium) that has a complex life cycle involving people and pigs. If someone ingests the larvae of the worm in undercooked pork, the worms develop into adults in the gut and their eggs pass in the person’s faeces. But if someone accidentally eats these eggs, they can develop into larvae in the person’s gut, where they can enter the bloodstream and travel to the brain before developing into mature adult worms.

“I was very surprised,” says Tovar. “I rarely eat pork. I don’t even like pork.”

Once they reach the brain, the worms cloak themselves in a jelly-like cyst to remain hidden from the immune system. As long as the worms are alive and maintaining their invisibility cloak, the body doesn’t realise they are there. When the worms die after about ten or twenty years, their disguise dissolves and the body realises it has been invaded. This provokes a massive immune response, causing life-threatening swelling and inflammation in the brain. This was the cause of Tovar’s headaches and vomiting.

After she was admitted to hospital, physicians performed emergency neurosurgery to remove the cyst and place a shunt to relieve the fluid that had built up in her brain. She received a course of medication over several weeks to kill any remaining parasites, followed by months of steroids to reduce brain swelling. Tovar finished her treatment successfully in April 2015 and is considered cured.

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