Minnesota: Como Zoo gorilla euthanized after long battle with effects of Baylisascaris infection

The Como Park Zoo and Conservatory in St. Paul, Minnesota announced the death by euthanasia of the 7-year-old western lowland gorilla, Nyati, on Tuesday.

Nyati has been suffering from medical deterioration over the years following an infection with the raccoon roundworm, Baylisascaris procyonis, in 2020.

According to zoo officials, Nyati contracted the parasite at a young age through environmental exposure. Though the parasite was successfully treated, it caused permanent lesions in her brain that led to ongoing challenges with movement, coordination, and motor function.

Over the past five years, Nyati’s care involved a coordinated and deeply committed effort from Como’s veterinary, animal care, and animal management teams. From physical therapy and custom habitat modifications to medications and regular assessments, her daily routine was centered on maximizing her comfort and wellbeing. Specialists from across the country were consulted over the years, but in recent months, her health continued to decline.

Earlier this month, updated medical imaging confirmed further neurological deterioration and musculoskeletal issues. With no meaningful options for recovery and based on comprehensive evaluations from her care team, the decision was made to allow her to pass peacefully—never waking from anesthesia during her final assessment. This was done intentionally to avoid additional stress and ensure her comfort every step of the way.

What is Baylisascaris procyonis?

Also known as the raccoon roundworm, B. procyonis is the most common and widespread cause of clinical larva migrans in animals. It is a ubiquitous roundworm infection of raccoons (Procyon lotor) and is emerging as an important helminthic zoonosis, primarily in young children.

Baylisascaris procyonis and related species are large nematodes of the order Ascaridia. Other, more familiar ascarids are Ascaris lumbricoides, Toxocara canis and Toxocara cati, nematode parasites of humans, dogs and cats, respectively.

Infection in Animals

The raccoon roundworm is indiscriminate in what animals it can infect, with more than 90 species of wild and domestic animals being identified as infected with B. procyonis larvae. Outbreaks of fatal central nervous system disease have occurred on farms, in zoos and research animal colonies and have affected commercial chickens, quail, pheasants and domestic rabbits. Many times these animals get infected by getting the eggs in their fur and then ingesting the eggs during grooming. In nature, small birds and mammals (particularly rodents) are infected by ingesting infective B. procyonis eggs while foraging for food at preferred sites of raccoon defecation.

When a species of animal other than a raccoon swallows these eggs, the microscopic larva hatches out in the intestine and then burrows through the wall of the intestine and begins migrating through the body trying to find a home. The body tries to kill the larva and it moves rapidly to escape attack. The larva seems to have a preference for lodging in the liver, eyes, spinal cord or brain. Occasionally, they can be found in other organs. When a larva tries to make a home, it causes a great deal of damage as the body tries to either wall it off or kill it. Eventually it dies and is reabsorbed by the body. In very small species such as mice, it might take only one or two larvae in the brain to be fatal. If the larva does not cause significant damage in vital organs, then the victim will show no signs of disease. Species other than the raccoon that are affected with this parasite CANNOT pass it on to anyone else. This is the end of the line for the larva and it never becomes a mature adult capable of producing eggs.

B. procyonis in Raccoons

Baylisiascaris procyonis is indigenous in North American raccoons that are very common in rural, suburban and urban settings where they are well adapted living alongside humans. Raccoons thrive in areas where there is a permanent water supply, available food, and suitable sites for dens. Some of the highest raccoon densities are in and around suburban and urban residences and parks. Gardens, garbage cans, bird feeders and pet food provide ample food for the raccoon.

In North America, the prevalence of Baylisascaris procyonis in raccoons is highest in the Midwest and Northeast where an infection rate of up to 80% has been reported. In the Southeast where the risk is lower, Baylisascaris procyonis is becoming an emerging infection in raccoons.

Baylisascaris procyonis causes little to no clinical disease in the raccoon. They become infected in one of two ways: 1) Young raccoons become infected by ingesting eggs during exploring and grooming activities with other members of their social group; 2) Adult raccoons acquire the infection by ingesting intermediate hosts (rodents, rabbits, birds) infected with the larvae of B. procyonis. The disease in the intermediate hosts listed above makes them easy prey for raccoons.

Baylisascaris procyonis: The little known but very dangerous raccoon roundworm

Raccoon Latrines

Raccoons habitually defecate in communal sites called latrines. This can be natural or man-made structures. Common urban and suburban sites are rooftops, attics, in and around chimneys, tree stumps, woodpiles, decks and lawns (near trees). If there are many raccoons in the area, there are likely to be large amounts of resistant B. procyanis eggs in the area. In the raccoon, adult females produce approximately 150,000 eggs/worms/day. The average raccoon sheds an average of 20,000 eggs per gram of feces. Because of the quantity and the resistance to environmental conditions, it is possible to have heavy and widespread contamination.

Risk to Humans and Disease

There are two factors that put people at risk for infection: 1) contact with raccoons, their feces, or the contaminated environment and 2) geophagia of pica. Humans who accidentally come into contact with active or abandoned latrines are at risk. Young children are at particular risk because of the habit of placing their fingers or objects in their mouths.

Larval migrans is the prolonged migration and persistence of helminth larvae in the organs and tissues. Disease manifestations of human baylisascaris include visceral, neural and ocular larva migrans.

The clinical manifestations of severe disease include eosinophilic encephalitis, permanent neurological damage, ocular disease and blindness, and death.

Baylisascariasis does not spread person-to-person.

Symptomatic infection in humans is relatively rare with less than 3 dozen cases reported; however, a University of Georgia study several years ago suggests there can be asymptomatic infections.

Treatment for this parasite is generally ineffective in preventing death. If the treatment is started early enough, it could kill the larva before it enters the central nervous system.

How can you prevent this potentially life-threatening infection? According to the Centers of Disease Control and Prevention the following steps should be followed:

• Avoid direct contact with raccoons — especially their feces. Do not keep, feed, or adopt raccoons as pets! Raccoons are wild animals.
• Discourage raccoons from living in and around your home or parks by:
o preventing access to food
o closing off access to attics and basements
o keeping sand boxes covered at all times, (becomes a latrine)
o removing fish ponds — they eat the fish and drink the water
o eliminating all water sources
o removing bird feeders
o keeping trash containers tightly closed
o clearing brush so raccoons are not likely to make a den on your property