2023-10-06 05:45:34
As reported by the team of Sanjaya Senanayake, from the Australian National University in Canberra, this is the first known case of infection of humans by this roundworm typical of snakes.
But if we look closer, Ophidascaris robertsi is not strictly reserved for snakes. What the doctors found in their patient’s head was only the third larval stage (called “L3 stage”) of the worm. However, this stage generally attacks mammals. The roundworm actually has a life cycle that is described as indirect, which means that it needs to pass through several host species to develop.
The eggs, excreted by the adult worm, are dispersed in nature through the snake’s excrement. Small marsupials, rodents or even koalas ingest the eggs, and the L3 larvae develop in their bodies. It is only when a python devours the intermediate host (the koala, the marsupial or the rodent, therefore) that the parasite re-enters a snake in larval form, develops there, becomes an adult and begins its turn to lay eggs. The cycle is then completed.
The lesion observed in the frontal lobe of the patient’s brain (A) was due to the presence of a parasitic worm (B, C) which had developed from a larva of the parasite Ophidascaris robertsi.
© Hossain, M. et al. : Human Neural Larva Migrans Caused by Ophidascaris robertsi Ascarid, Emerging infectious Diseases 29, 2023, fig. 2
Pythons, koalas and small rodents
It is therefore not a snake parasite which lodged itself in the woman’s head, but a larva specialized in infecting mammals. The specialists write in their report published in the specialist journal Emerging Infectious Diseases that the woman was probably infected with the eggs while consuming New Zealand spinach, a vegetable that grows wild there.
The Australian was first hospitalized in January 2022 due to abdominal pain and diarrhea, and subsequently developed a severe cough. Tests revealed damage to the lungs and liver as well as a massive influx of immune cells into the lung tissue. Both of these phenomena were likely due to the worm larvae spreading throughout his body.
Strictly speaking neurological problems followed: for three months, the patient complained of memory problems and depression. Finally, having decided to perform a brain scan, doctors discovered an abnormal area approximately 1.5 centimeters long and 1 centimeter wide, located just behind the forehead. Finally, while performing a biopsy, they found the pale red worm, measuring 8 centimeters long.
The defenseless brain
Once this was removed, and the patient was treated with medication against possible other larvae, the symptoms disappeared. How could a worm develop in the brain, first protected from various infections? It is possible that the initial treatment of lung inflammation, resulting in suppression of immune defenses, allowed the larvae to enter the brain and develop there.
Such a case is not as unusual as it might seem at first glance. Similar symptoms, called larva migrans, are also known in human roundworm, which infects around a fifth of the world’s population (this disease results in worms infesting different organs, and causing vision problems, asthma, pneumonia or skin rashes ). A wide variety of parasitic worms can enter the human central nervous system and trigger neurological symptoms. This is the case, for example, of raccoon roundworm. Baylisascaris procyonis, also common in Europe, which sometimes causes very serious, even fatal, meningitis. However, it is extremely rare for it to infect humans.
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