How much do you know about “brain-eating worms”?

Author: Su Huiting Peking Union Medical College Hospital

Reviewer: Du Juan Chen Yu, deputy chief technician, Peking Union Medical College Hospital

In 2023, the media reported that a 6-year-old boy traveled to Hainan with his parents. After returning home, he had a fever and was admitted to the ICU. He was diagnosed with "brain-eating worms". So, what are "brain-eating worms"? Do they really eat human brains? How do "brain-eating worms" infect humans?

1. What is a “brain-eating worm”?

The name "brain-eating worm" sounds very scary. Its scientific name is Balamuthiae baboonii, a parasite that can cause serious infection in humans. It is widely found in natural environments such as fresh water, silt, ponds, or dust. Balamuthiae baboonii parasites are considered to be "free-living" protozoa that can survive independently in the natural environment and obtain the nutrients they need to survive by preying on microorganisms and decomposing organic matter.

Figure 1 Copyright image, no permission to reprint

2. Do “brain-eating worms” really “eat brains”?

After the Balamuthiae baboon protozoan infects humans, the human brain tissue is destroyed by the parasites, leaving it full of holes as if it had been gnawed by insects. Therefore, Balamuthiae baboon is also vividly called the "brain-eating worm", but the parasite does not directly eat the human brain.

Specifically, after the baboon amoeba enters the human body through the mouth and nose, it enters the central nervous system and rapidly reproduces, and then spreads in the brain. Imaging manifestations include purulent meningoencephalitis (granulomatous encephalitis), hemorrhagic meningitis, or brain parenchymal necrosis.

Studies have reported that there are two types of central nervous system infections caused by "brain-eating worms": primary amoebic meningoencephalitis and granulomatous amoebic encephalitis. Primary amoebic encephalitis develops quickly, and it only takes a few days from onset to death. Patients will experience symptoms such as severe headache, fever, vomiting, photophobia, and abnormal mental behavior. Granulomatous amoebic encephalitis is subacute and has a long course, which can last from weeks to months. The clinical manifestations are headache, low fever, and visual impairment. If not diagnosed and treated in time, it will slowly develop into epilepsy, loss of consciousness, coma, and even death.

Figure 2 Copyright image, no permission to reprint

3. How do “brain-eating worms” infect humans?

Epidemiological data show that the high-risk population for infection with Balamuthiae baboon is usually workers who are exposed to soil in agriculture, gardening, ranching, etc. It is generally believed that there are two ways of infection with "brain-eating worms": 1. Through agricultural work, skin with skin lesions or trauma comes into contact with contaminated soil, or dust in the environment with baboon amoeba cysts enters the mouth and nose through the respiratory tract; 2. Water contaminated by baboon Balamuthiae baboon enters the mouth and nose by choking. People are generally susceptible to baboon Balamuthiae baboon, and those with underlying diseases and low immune function are more likely to cause baboon amoebic encephalitis.

The "brain-eating worm" not only attacks the nervous system, but also the skin. According to research reports, most infections caused by baboon amoeba in my country begin with skin damage. The clinical manifestations are red patches with clear boundaries and slight bulges around them. The rash is asymptomatic and often occurs on the face or the center of the limbs (especially the knees). If diagnosis and treatment can be carried out at the skin symptom stage, the infected person can basically be cured.

4. How far are the “brain-eating worms” from us?

From January 2023 to September 2024, Peking Union Medical College Hospital detected three cases of baboon Balamuthiae through pathogen metagenomic high-throughput sequencing technology (mNGS), including a 71-year-old male who had the habit of swimming outdoors and had choking recently; a 56-year-old woman who had fallen into feces and water 2 months before the onset of the disease; and a 45-year-old woman with low immune function, working in a restaurant, and having a history of contact with raw meat. All of the above patients had Balamuthiae in their cerebrospinal fluid, and were in critical condition with a poor prognosis.

5.What are the diagnostic methods for “brain-eating worms”?

Early diagnosis and treatment are necessary to prevent brain-eating worms from eating your brain. The following are common diagnosis and treatment methods.

(1) Epidemiological history: It is the key to clinical diagnosis. You should be careful to clearly inform your doctor of your contact history, such as exposure to silt, ponds, soil, etc.

(2) Brain tissue or skin biopsy.

(3) Immunohistochemistry (IHC): Use specific antibodies against amoeba to detect amoeba.

(4) Indirect immunofluorescence assay (IFA): used to detect antibodies produced against amoeba in the serum of infected patients.

(5) Pathogen metagenomic sequencing (mNGS): This method is the main detection method used in the literature to assist in the diagnosis of amoebic encephalitis.

6. How to treat infection with the brain-eating worm?

Although the "brain-eating worm" is terrifying, its infection incidence rate is very low; once it invades the nervous system, the mortality rate is very high. At present, there are only more than 200 cases of patients infected with Balamuthia medulla obovata reported worldwide, so the potentially effective medication regimens for granulomatous amoebic encephalitis are summarized based on a few case reports, and it is almost difficult to test their effectiveness and safety through clinical trials. In vitro tests have shown that Balamuthia medulla obovata is sensitive to pentamidine thiocyanate and may be effective for patients. Other studies have shown that azithromycin, sulfadiazine, flucytosine, clarithromycin or methoprene have the effect of killing amoeba parasites.

7. How to prevent infection with the brain-eating worm?

(1) Do not swim in the wild! Do not engage in water activities in low-water or slow-flowing water.

(2) When participating in activities in hot springs, ponds, and other untreated fresh water, keep your head above the water or use a nose clip to prevent choking.

(3) Avoid digging or disturbing the silt or sand at the bottom of freshwater ponds.

(4) Try to avoid washing your face with outdoor water, and do not drink outdoor water at will; especially if you have open wounds on your body, avoid contact with all kinds of outdoor water and mud.

(5) Enhance self-protection awareness, especially for agricultural and animal husbandry workers who are exposed to soil for a long time; if there are skin lesions or injuries, special attention should be paid to avoid direct contact with soil.

(6) Wear a mask when engaging in agricultural and animal husbandry work to prevent dust, sewage, aerosols, etc. from entering the mouth and nose.

(7) If you experience symptoms such as skin erythema, fever, headache, nausea and vomiting, or poor mental state after participating in the above activities, please seek medical attention immediately.

References

[1]Lorenzo-Morales J ,Cabello-Vílchez, Alfonso Martín,Martín-Navarro, et al.Is Balamuthia mandrillaris a public health concern worldwide?[J].Trends in Parasitology, 2013, 29(10):483-488.

[2] Another case of brain-eating worm infection! The child is in critical condition and admitted to the ICU. Effective drugs are still under development. 2023-06-28 Lu Qilin Original: Medical Pediatric Channel.