Dear Doctor: My family is planning a trip to Hawaii in a few months, and we've been hearing about a condition called rat lungworm disease. What is it? And is there anything we can do to prevent infection?

Dear Reader: Rat lungworm, a disease that affects the spinal cord and the brain, is caused by a roundworm known as Angiostrongylus cantonensis. It's a parasite, which means it requires a host to live, grow and reproduce. Although rat lungworm disease is most commonly found in Southeast Asia, the Caribbean and certain tropical Pacific islands, it is now established in Hawaii. So far in 2017, at least nine cases of rat lungworm disease have been reported throughout the state.

As with a number of other previously rare or site-specific diseases, international travel, trade and shipping are playing a role in expanding the parasite's reach. In recent years, the roundworm that causes the disease has also been found in Alabama, Florida, Louisiana and California.

The adult form of the roundworm lives in rats, which excrete the larvae in their stool. When snails and slugs feed on infected rat stool, they become carriers of the parasite. Larvae may also be found in freshwater prawns, crabs, frogs and fish. People become infected when they eat raw or undercooked portions of these foods. Some individuals report becoming infected by eating vegetables, fruit or salad greens that were not properly washed and were contaminated by snails or slugs.

Once the larvae enter the human body, they burrow through the walls of the digestive tract and enter the blood vessels. This eventually brings them to the meninges, the membrane that surrounds the brain and spinal cord. But because humans are not appropriate hosts for this roundworm, the larvae soon die.

It's the presence of these dead larvae in the cerebrospinal fluid that results in harm to humans. They trigger the release of a flood of white blood cells known as eosinophils, one of whose jobs is to attack foreign substances. This outpouring of white blood cells results in severe inflammation known as eosinophilic meningitis.

Symptoms, which can include headache, stiff neck, hypersensitive skin, visual disturbances, fever, nausea and vomiting, vary from person to person. The disease lasts from one week to several months and resolves on its own. In rare cases, it can result in coma or death.

As for what you can do to protect yourself, the state of Hawaii and the Centers for Disease Control and Prevention offer the following advice:

-- Thoroughly wash all salad greens, raw fruit or vegetables under running water.

-- The snails and slugs that carry rat lungworm larvae can be quite small and easy to miss. This means you must wash leafy greens piece by piece, both front and back. Be sure to examine them closely before adding them to a meal.

-- When dining out, ask your server whether all fresh produce is carefully cleaned.

-- If you order freshwater prawns or fish, ask that they be cooked to an internal temperature of at least 165 degrees.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I recently had an annual physical and everything seemed normal. But the bottoms of my feet feel as if they're on fire. What could be the cause? And what can I do?

Dear Reader: The symptoms that you describe sound typical for polyneuropathy (sometimes termed peripheral neuropathy). Polyneuropathy is usually related to degeneration of the part of the nerve cell (the axon) that conducts nervous impulses between nerve cells. Nerve cells with longer axons -- the ones that go to the feet -- are affected first, and the burning and tingling symptoms, often first noticed at night, can interfere with sleep.

Diabetes is the most common cause of polyneuropathy. Constant elevations of blood sugar lead to decreased blood flow to the nerves and, potentially, nerve inflammation. This affects the nerves' ability to process sensation and, when diabetes is severe and longstanding, can lead to the complete loss of sensation in the feet. Symptoms can subside once blood sugar is under control. This seems an unlikely diagnosis in your case because, if you had diabetes, your doctor would have mentioned it.

Low thyroid levels (hypothyroidism) also can lead to polyneuropathy. Initial symptoms can be a burning or loss of sensation in the feet. Rarely, this can also lead to muscle weakness in the legs. Your doctor may have already checked your thyroid level with a blood test during your physical. If caused by hypothyroidism, the symptoms would improve with thyroid hormones.

B12 deficiency -- detectable by a blood test -- is a possible cause as well, but it's generally found only among people who are malnourished, following a vegan diet or who have problems absorbing B12 in the small intestine. While rare, B6 deficiency can also cause polyneuropathy; a more common cause of polyneuropathy is B6 toxicity from mega doses of B6.

Conditions like HIV and Lyme disease can lead to polyneuropathies, as can an elevation of immunoglobulins seen in bone marrow conditions such as multiple myeloma and Waldenstrom macroglobulinemia. The latter can be assessed by checking the blood's immunoglobulin levels.

Exposure to certain medications, chemotherapies or heavy metals can cause polyneuropathy as well. One widely available toxic chemical, alcohol, also can lead to nerve damage in the lower legs. In a survey of 107 patients with chronic alcoholism, 32 percent suffered from neuropathy in the lower legs. This alcohol-induced nerve dysfunction can also affect the nerves to the muscles, causing weakness, as well as the nerves to both the bladder and intestines, causing urinary and bowel problems.

Lastly, polyneuropathies can occur in genetic disorders. These are often diagnosed by a neurologist and identified only after other causes have been ruled out. Even after an exhaustive search, a reason for the neuropathy may not be found.

I would make mention of these symptoms to your doctor. If you drink alcohol consistently and heavily, you should stop. Similarly, if you're taking large doses of B6, stop this as well.

In any case, polyneuropathy should not be ignored. It often has a cause that needs to be investigated further.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: The Food and Drug Administration recently said parents shouldn't give their kids medicine with codeine or tramadol. Just how dangerous are these drugs? And what should parents use instead?

Dear Reader: Codeine and tramadol are medications that are widely used to treat pain. However, not everyone reacts to these drugs the same way. Some individuals metabolize codeine and tramadol very quickly, which results in unsafe levels of the drugs in the body. This puts them at risk of breathing problems severe enough that they can lead to death. As a result, the FDA amplified an existing warning in April regarding the use of tramadol and codeine when treating children.

In its announcement, the FDA said that children younger than 12 should not be given medications that contain either codeine or tramadol. This warning also extends to nursing mothers, who risk transmitting unsafe amounts of the drugs through their breast milk. The FDA also states that tramadol is not to be used to treat pain from surgeries to remove tonsils or adenoids in children under 18 years old.

Manufacturers of drugs that contain codeine or tramadol are now required to change their labels to include a plainly stated warning against their use in anyone under the age of 12, and by nursing mothers. An additional warning cautions against giving codeine or tramadol to adolescents between the ages of 12 and 18 who are obese, or who have sleep apnea, lung disease or any other condition that can affect breathing.

So what exactly are codeine and tramadol, and why do they pose dangers to some younger patients?

Both drugs belong to a class of medications called opiate analgesics. Codeine is approved to treat pain and, because it also belongs to a class of medications called antitussives, it is used to treat cough. Antitussives don't cure a cough, but rather suppress the command from the brain that tells the body to cough. Codeine and tramadol reduce pain in a similar fashion, by acting on neural pathways.

As we mentioned earlier, the problems arise in certain individuals whose bodies absorb and metabolize the drugs very quickly. An enzyme variant in their livers causes them to convert the medications so rapidly that they wind up with unsafe levels of active opioids in their bloodstream. This affects the part of the brain that regulates breathing and can lead to death.

The new warning comes thanks to data collected by the FDA, which showed that some children who were given codeine or tramadol became gravely ill after just a single dose of the medication. The warning to nursing mothers arises from the report of an infant who died after being exposed to codeine in his mother's milk.

As for what you should use instead, in most cases, over-the-counter medications like Tylenol or ibuprofen should do the trick. If not, check with your family doctor to discuss and craft a pain management plan that is both effective and -- here's the really important part -- safe for your child.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)