Hello again, dear readers, and welcome to another edition of our ongoing conversation. We're very happy that, a little more than a year into our column, we continue to hear from you. How are your New Year's resolutions faring thus far? If you have any success stories, or thoughts on how to stay (or get back) on track, we'd love to hear them.

-- We've received a lot of feedback on the column about nurse practitioners (also referred to as NPs) and physician assistants (also known as PAs). Several letter-writers corrected our use of an apostrophe in referring to the profession of physician assistant. It may seem trivial but in fact there's a crucial difference between "physician's assistant" and "physician assistant," and it's about autonomy. A physician assistant is a clinician in her or his own right. We regret (and won't repeat) the error.

-- In that same vein (and in the same column) we neglected to fully state the educational requirements to become a nurse practitioner.

Vicki, whose daughter is a NP, filled in the details:

"Nurse practitioners must have a Master of Science in nursing," she wrote. "At the University of Memphis, the NP must take an exit exam about four weeks prior to graduation (with a passing grade), or you don't graduate with that class (extra pressure!). Once the exit exam is passed, the NP has to take state boards to actually become licensed."

Sandra, an Advanced Practice Registered Nurse (APRN) in Kansas, points out that a Master of Science is, in fact, the minimum educational requirement for a nurse practitioner:

"In our state, NPs will no longer be able to enter practice with a master's degree," Sandra wrote. "Entry into practice will require a doctorate, usually a DNP -- Doctorate of Nursing Practice. In addition to the undergraduate nursing degree, NPs have hands-on nursing practice prior to going on to advanced practice, which requires hundreds of hours of clinical training."

And Rich, a physician assistant in Massachusetts, wrote to say NPs and PAs are integral to the functioning of most hospitals and medical centers:

"Many NPs and PAs work in ICUs, often seeing the most complex patients, so this work is not just left to doctors. As any new resident in the ICU will tell you, it's an experienced ICU nurse who helps guide inexperienced interns and residents through the ICU, and likely other rotations as well. Medicine is more team-oriented today than ever before.

"Also, more and more academic medical centers have residency programs in oncology, surgery, cardiology and other fields of medicine for PAs, so they can get advanced training."

We thank all the nurse practitioners and physician assistants who took the time to write regarding the column. One thing the letters had in common was a deep passion for medicine and an even deeper concern for the patients you treat. We agree with you that the practice of medicine is a calling, and we are both proud and honored to be your colleagues.

For readers who want to learn more about these specialties, visit the American Association of Nurse Practitioners at aanp.org and the American Academy of Physician Assistants at aapa.org.

(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: What, exactly, is kratom? The FDA has apparently called it an opioid, even though it seems to be an herbal supplement. Is it safer than prescription opioids? I'm afraid of opioids, but if this is safer, I'll try it.

Dear Reader: Before we start, let's reflect just a moment on the opioid epidemic in America. The origin of this epidemic stems from the medical community's desire to control pain: Pain was the enemy and opiates were the cure. But over the years, the addictive potential of these drugs has destroyed multiple lives. As a society, we're now using other medications to control pain, while actively searching for more.

Some consider kratom (Mitragyna speciosa), a tree native to southeast Asia, to have potential in this respect. Kratom has been used in traditional medicine since the 1800s, with the leaves of the tree chewed or made into a tea. These leaves contain many compounds, but two specifically -- mitragynine and 7-hydroxymitragynine -- appear to have the primary pain-relieving effects. These compounds attach to and stimulate the mu-opioid receptor in the brain, creating positive reinforcement, while blocking the pain-relieving effect on two other opioid receptors. Kratom also contains chemicals that attach to other brain receptors, possibly encouraging calm. Further, because kratom is part of the caffeine family, the tree's leaves also appear to have stimulating effects.

People who have used kratom have reported pain relief, relaxation, improved mood and decreased anxiety. Because of its pain-relieving mechanism and because it works via the opiate receptors, kratom has been considered a potential alternative to traditional opiates, with perhaps even the ability to help wean people off opiates.

We already have some history with the substance, because kratom has been available in the United States since 2010. One study, from 2017, surveyed 500 men and women in recovery centers about their use of kratom. About 21 percent had used kratom once, and 10 percent had used it in the past year. Kratom users were more likely to be college-educated and younger than addicts who had never used kratom. In fact, many had used kratom to deal with their opiate addiction.

Although these findings could suggest that kratom may hold promise against pain and opiate addiction, we simply don't have good studies of its effectiveness.

And it may have serious side effects. The substance is cleared from the body through the liver, so if a person has liver problems or is taking medications metabolized by the liver, it may stay in the bloodstream. From 2010 through 2015, 660 calls were made to poison control regarding kratom; 65 percent of these callers had used kratom by itself, without additional substances. Callers complained of rapid pulse rates, agitation, drowsiness, nausea and elevated blood pressure.

Symptoms can be amplified to life-threatening levels when kratom is mixed with alcohol and prescription or illicit drugs, sometimes leading to liver toxicity, seizures and death. Kratom was linked to 15 deaths between the years 2014 and 2016; of note, these deaths do not appear related to use of kratom with other drugs -- just kratom alone. That said, the number of deaths from prescribed opiate medications far outnumber the deaths thus far from kratom.

In summary, although the potential for abuse of kratom appears less than that for more traditional opioids, the fact remains that kratom does work on the mu-opioid receptor, meaning it can be abused. That potential prompted the FDA to recently warn of kratom's opioidlike properties and potential for risk.

In short, we need more studies of kratom -- and better replacements for opioids. As of now, I would look for other ways to manage pain.

(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 read a terrible story about a couple who went to the Caribbean and got hookworms by going barefoot. Is that only possible in the tropics, or should I be worried here in the United States? I hate wearing shoes in the summer.

Dear Reader: Let's start with a recap of the story. A couple visiting a Caribbean resort came home with more than a tan. After a barefoot walk on the beach, their feet began to itch. They chalked it up to bug bites and, amid much scratching, continued their vacation. Once home, however, they developed large, weeping blisters on their feet, followed by subcutaneous markings that looked as though something might be burrowing beneath their skin.

It was. During that barefoot stroll, the couple had unwittingly walked through an area contaminated by hookworm larvae. Larvae are present anywhere that an infected animal (or human -- a bit more on that in a moment) has left its stool. In this case, the hookworms were a species that lives in the intestines of dogs, cats and wild animals. This was actually good news because humans are imperfect hosts for this particular parasite: In other words, the larvae can't mature or reproduce. As a result, infections typically resolve without medication in about four to six weeks. (In the couple's case, once the infection was identified by inspection of a stool sample, they were given a course of antiparasitic drugs.)

The key to understanding what happened lies in the life cycle of the hookworm. The parasite, a nematode, thrives in moist, warm areas and thus is common in the tropics and subtropics. Its eggs are deposited into the soil via the feces of an infected host. After the eggs hatch and the larvae mature, they are ready to burrow into the skin of whichever creature crosses their path.

When hookworm larvae enter their ideal host, they become a serious health threat. They complete a complex journey through the body that brings them to their final destination, the inside of the small intestine. Once there, they latch onto the intestinal walls with the hook-like mouths that give them their name, and begin to feed on the host's blood.

Two different species of hookworm can infect humans -- Necator americanus and Ancylostoma duodenale -- with the former the more prevalent. At least 575 million and up to 740 million individuals are affected by hookworm, making it one of the most common parasitic infections in the world. Without treatment, infection by these species causes severe anemia. Over time, this results in weakness, extreme fatigue, shortness of breath and irregular heartbeat. Children with hookworm infection often have stunted growth and cognitive problems, and become susceptible to other illnesses. Adults become so exhausted that they cannot function fully.

Although infection by N. americanus was once a grave public health problem in the United States, particularly in the Southeast, it is now quite rare, thanks to education and eradication programs, as well as improvements in sanitation. However, hookworms that infect pets and wildlife remain common. If a barefoot walk were to take you across soil contaminated by the feces of an animal (or human) infected with hookworm, then you could indeed be at risk.

(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.)