What is Angiostrongylus Cantonensis Infection (Rat Lungworm)?
Angiostrongylus cantonensis is a type of worm – specifically known as a metastrongyloid nematode – and is one of the most common causes of a type of brain inflammation called eosinophilic meningitis. This worm is also known as the “rat lungworm” because it’s usually transmitted by rats, snails, and slugs. While this parasite is most common in the Asia-Pacific region, there have also been incidents and isolated cases in other parts of the world.
There are nine different types of these worms, but two types – A. cantonensis and A. costaricensis – are the most likely to cause disease in humans.
What Causes Angiostrongylus Cantonensis Infection (Rat Lungworm)?
Rats serve as main hosts for a particular kind of worm. The adult worm will enter the rat’s bloodstream and grow there. When the worms become fertile, they lay eggs into the rat’s blood. These eggs will then get stuck in small blood vessels in the lungs, where they will hatch. These baby worms find their way into the airways of the lungs. From there, they move to the throat, are swallowed, and pass through the digestive system until they end up in the rat’s feces.
Snails and slugs, which serve as middlemen in this process, eat these baby worms. Once inside snails or slugs, the worms grow into their next stage. These mature worms can then reenter a rat or other hosts when these hosts eat infected snails or slugs.
Inside these hosts, these mature worms tend to be attracted to the nervous system and grow into young adults in their brains. The worms then move into the bloodstream, finally making it back to the lungs where they become fully grown, and female worms lay more eggs.
Other creatures, like frogs, lizards, and some types of seafood, can also accidentally pick up these worms by eating infected snails or slugs. Even vegetables that have slime from snails on them can potentially spread the infection.
Humans can get infected in the same way, typically by eating infected animals or vegetables with snail slime on them. Once inside a human, the worms go through a similar life cycle, burrowing from the intestines into the bloodstream where they mature. The adult worms lay eggs in the lungs’ arteries, which hatch and then make their way to the throat to be coughed up. Afterward, these are swallowed and finally released through the feces.
Just like in the rat, these worms can end up in the human’s brain where they grow into adults. From there, they return to the heart, finally ending up in the lungs’ blood vessels where they lay more eggs. The worms can cause a strong immune response in humans, especially in the fluid-filled space beneath the spider-web-like layer covering the brain, leading to a serious form of meningitis. With a serious infection, it can cause more severe inflammation resulting in nerve root inflammation, nerve disorders, spinal cord inflammation, mental confusion, coma, and even death. The worm ends up dying in the nervous system, and because of this, humans can’t pass the worms onto others.
These worms can show symptoms in as short as 1-3 weeks but in some cases could take up to 6 weeks.
Risk Factors and Frequency for Angiostrongylus Cantonensis Infection (Rat Lungworm)
The Angiostrongylus species, also known as the rat lungworm, is a parasite mainly found in Asia-Pacific regions, particularly Thailand and Malaysia. It can also be found in the Pacific basin, China, Vietnam, the Phillippines, Taiwan, and Hawaii. The spread of infected rats has led to the parasite appearing in parts of Africa, South America, Australia, Caribbean islands, New Orleans, and Louisiana. There have also been occasional cases in Europe and the United States due to travel-related exposure.
This parasite lives in rodents and certain mollusks in a natural cycle. Yet, it can also infect sea animals like crabs, shrimp frogs, even though it can’t reproduce inside these animals. Despite this, people can still get infected if they consume these parasites. Essentially, humans are a dead-end host for this parasite.
Because this infection is mainly in East Asia, it is likely spread to western countries through travel of infected rats and mollusks on ships. Notably, certain mollusks, such as the giant African land snail and Parmoarion martensi from southeast Asia, have made their way to places like Hawaii. In Hawaii, infection with the A cantonensis (species of the parasite) is a reportable disease, with several outbreaks recorded. Likewise, there have been cases of disease outbreaks of A cantonensis in Taiwan and China due to backflow travel from South America during ship transport.
Signs and Symptoms of Angiostrongylus Cantonensis Infection (Rat Lungworm)
The medical condition A cantonensis triggers a severe inflammatory reaction as the parasites die. The most common manifestation of this is eosinophilic meningitis (EoM). Usual symptoms include persistent headaches, neck stiffness, nausea, vomiting. Additional symptoms may last for several weeks and include abnormal sensations like tingling or increased sensitivity to touch and temperature. There’s also a more serious but less common condition called eosinophilic encephalitis (EoE), which is usually fatal due to delayed diagnosis. On rare occasions, individuals may experience eye symptoms like feeling as if a foreign object is in the eye or blurred vision.
During the course of this infection, patients may also endure severe headaches unresponsive to regular painkillers, sensitivity to touch, tingling, and a burning sensation. Other notable characteristics of this disease are shifting abnormal sensations, as well as migrating pain in the trunk and limbs. In some situations, paralysis of the sixth or seventh cranial nerve may be observed. Additionally, reasons are not entirely clear as to why patients might also experience problems with urination.
Before neurological symptoms become significant, patients typically experience gastrointestinal issues. Following initial exposure to the pathogen, symptoms take approximately 1 to 3 weeks to surface, but this may extend up to 6 weeks. During this period, patients might experience vague abdominal pain, nausea, and vomiting due to the invasion of the intestinal wall by the larvae. These larvae then enter the bloodstream and eventually cross the barrier into the brain, causing neurological symptoms. Interestingly, this phase can last from a week to several weeks, during which patients may experience alleviation of initial digestive symptoms and may feel symptom-free or continue to have gastrointestinal symptoms. Vomiting may also occur due to meningitis. General malaise, low-grade fever, sleep disturbances, and confusion are other nonspecific symptoms patients may experience. Interestingly, children may show less visible neurological symptoms compared to adults but demonstrate more digestive system involvement. A complete neurological and abdominal examination is usually suggested in these cases.
Testing for Angiostrongylus Cantonensis Infection (Rat Lungworm)
Diagnosing neuro-angiostrongyliasis, a parasitic worm infection, involves looking at your medical history, signs and symptoms that align with the disease, and supportive lab results. Doctors will consider if you have traveled to or lived in an area where the infection is common, or if you have eaten undercooked food or raw veggies possibly contaminated with snails, slugs, crab, shrimp, or similar creatures.
In the lab, one of the main indications of neuro-angiostrongyliasis is an increase in white blood cells, particularly eosinophils, in your cerebrospinal fluid (CSF) – the fluid that surrounds and protects your brain and spinal cord. A high number of eosinophils (usually more than 10%) in your CSF, especially when it aligns with your symptoms, can suggest the diagnosis. Remember, the percentage of eosinophils in the CSF is considered high if it’s more than 10% of total white blood cells in the CSF or exceeds 10 eosinophils per every microliter of CSF fluid. An elevated protein level is another indication. At times, a lesser increase in eosinophils is found in the blood, but it doesn’t necessarily align exactly with the numbers in the CSF or with how your illness is progressing.
Interestingly enough, the presence of the worm larvae in the CSF during a spinal tap can also confirm the disease, making for a unique diagnosis experience. Brain scans using CT or MRI aren’t usually that helpful in confirming what’s causing the condition.
There are more specific lab tests that can help with the diagnosis like dot blot ELISA or western blot, but these are not available everywhere. Similarly, PCR tests, which identify the infection’s genetic material, can be quite accurate, but are also not widely available.
Another condition called gnathostomiasis, also causing an increase in eosinophils, could mimic this infection. This condition usually presents with root like pain. The presence of blood in the CSF or changes in the brain seen on imaging may point towards gnathostomiasis rather than neuro-angiostrongyliasis.
Treatment Options for Angiostrongylus Cantonensis Infection (Rat Lungworm)
The severity of symptoms in patients with parasitic infections can vary widely depending on how many parasites are in the body. While symptoms can often go away on their own with just simple care, the main goal is to lessen inflammation in the lining of the brain and spinal cord and lower pressure inside the skull by draining spinal fluid and relieving headache symptoms.
Doctors may administer steroids, specific drugs that lower inflammation, which have been shown in some studies to lessen the duration of headaches and reduce the need for repeated spinal fluid drainage procedures. While traditional medical advice did not recommend the use of anti-parasite medications due to the potential of causing an over-the-top inflammatory reaction as the parasites die, this approach is changing. It’s now understood that combining anti-parasite therapy with steroids is safe and can be especially beneficial for those with a high number of parasites in the body.
About 1% of all reported cases involve ocular angiostrongyliasis, a condition where the larva enters the eye, causing symptoms like blurry vision, blindness, and pain. The exact way the larva gets into the eye is still not fully understood, but it’s thought that it might travel along the artery connected to the retina, situated between the optic nerve and its covering. Generally, only a single larva is present in these cases, and individuals typically have eosinophilic meningitis as well. This eye condition requires laser treatment to kill off the larva before they can be surgically removed.
There aren’t any official guidelines for treating these parasitic infections. But, based on current scientific understanding, these recommendations are generally followed: In Hawaii, a test can be performed on the spinal fluid to detect the presence of parasite DNA. If an infection is suspected early on, this test can be repeated. Testing against antibodies which the body might produce in response to the infection is not recommended. If prescribed, a medicine called Albendazole, an anti-parasitic, can be used along with steroids to control the intense body’s response to dying parasites. However, special care should be taken for diabetic patients to control their blood sugar levels.
What else can Angiostrongylus Cantonensis Infection (Rat Lungworm) be?
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To accurately diagnose patients, we need to be particularly suspicious of those who might have come into contact with a certain kind of worm (nematode) in the weeks leading up to their symptoms, potentially even as long as six weeks before. Other infections that can cause a specific kind of inflammation in the brain (eosinophilic meningitis) need to be considered as well, such as:
- Gnathostomiasis, which often comes from eating undercooked fish, chicken, or snake meat
- Baylisascariasis, which usually affects children who unknowingly ingest soil contaminated with eggs of the Baylisascaris procyonis parasite (usually found in raccoon feces)
- Cysticercosis, schistosomiasis, and paragonimiasis, diseases caused by different parasitic infections
- Coccidioidomycosis, which is also linked to eosinophilic meningitis
Moreover, non-infectious causes of a type of brain inflammation (eosinophilic leptomeningeal enhancement) can include conditions like non-Hodgkin lymphoma, blood disorders (myeloproliferative disorders), a type of brain cancer (glioblastoma), and conditions relating to lung cancer (paraneoplastic manifestation from bronchogenic carcinoma).
Mentionably, certain medications can also provoke eosinophilic meningitis. These include trimethoprim-sulphamethoxazole, ciprofloxacin, ibuprofen, intraventricular vancomycin, and gentamicin.
It’s worthwhile to note that mental confusion and neurological deficits have been associated with an illness called idiopathic hypereosinophilic syndrome.
What to expect with Angiostrongylus Cantonensis Infection (Rat Lungworm)
The outcome for patients with eosinophilic meningitis, which is a rare inflammation of the membranes covering the brain and spinal cord, largely depends on how quickly the disease is correctly diagnosed. Detecting this disease requires a strong clinical suspicion for a specific cause, called A cantonensis, and certain findings in the spinal fluid.
In some instances, the infection could resolve itself while in others, depending on the severity, it might unfortunately lead to death. The situation is complicated by the fact that there is not enough data on the prevalence of this disease on a national level.
Furthermore, the lack of extensive diagnostic tests and a general lack of awareness among healthcare providers make it hard to predict the outcomes. In other words, due to these challenges, it’s difficult to assess how the disease might turn out for different patients.
Possible Complications When Diagnosed with Angiostrongylus Cantonensis Infection (Rat Lungworm)
Some of the potential consequences of this condition may include death due to a particular type of meningitis called eosinophilic meningitis or lasting blindness. Eye infection, called ocular angiostrongyliasis, occurs in about 1% of all reported cases. This happens when a larva enters either the front or back part of the eye. Scientists do not fully understand how the larva gets into the eye, but it is suspected to travel along the retinal artery located between the optic nerve which transmits visual information from the eyes to the brain and the protective covering of the nerve. Generally, only one larva is found in the eye and can cause blurred vision, blindness, and pain. Usually, folks with this eye infection also have eosinophilic meningitis.
Potential consequences:
- Death from eosinophilic meningitis
- Long-term blindness
Ocular angiostrongyliasis complications:
- The larva entering the front or back part of the eye
- Blurred vision
- Blindness
- Pain
Often accompanied by:
- Eosinophilic meningitis
Preventing Angiostrongylus Cantonensis Infection (Rat Lungworm)
Angiostrongyliasis, a type of infection, has been linked to eating certain creatures like crabs, snails, slugs, and prawns, which can carry the species A cantonensis. If local instances of this condition are noticed, they ought to be reported to the appropriate public health authorities. This helps to prevent further consumption of infected creatures and control the source of the infection. It’s vital to make public aware of the risk attached to eating these creatures raw or undercooked.
The main way this infection is caught is by eating these animals raw. To avoid this risk, consumption of raw snails, slugs, crabs, and shrimp should be avoided. Sometimes, raw snails or slugs can accidentally end up in uncooked foods like salads. As such, paying attention in food preparation and thorough hand washing can significantly help in reducing the risk of catching this infection.
