Eucalyptus Leaves–More than a Delicacy for Koalas

koalaEven the eccentric Sheldon Cooper, from the hit TV show The Big Bang Theory can’t resist the sight of cute koalas munching on eucalyptus leaves. Those familiar with Sheldon Cooper’s character would find this rather strange; after all, it is quite unlike him to be fascinated by superficial matters. Avid fans would dig deeper to discover that these seemingly cute and cuddly creatures may actually bear a unique scientific and medicinal connection.

Although koalas resemble bears, the koala is not a bear but a marsupial. These creatures are famously known for being very picky eaters. And what they pick are eucalyptus leaves. Because these have high water content, most koalas meet their water requirements by simply dining on the leaves.  Surprisingly, eucalyptus leaves are poisonous to most animals and humans. So how do koalas safely process the leaves’ toxic chemicals? It has to do with the unique microbes that inhabit the animals’ digestive tract. Not only can these bugs break down the poisonous compounds they’re passed on from mother to baby koala. But not in the way you might think. To be armed with the microbes without which they could not survive, baby koalas eat their mothers’ feces. Yes, that’s right! Once koalas ingest these feces, termed “pap,” their bodies will acquire natural defenses to remove the toxins emanating from the eucalyptus oils.

Humans can’t safely ingest eucalyptus. However, clinical studies have indicated that eucalyptus leaves and its oils have promising antifungal and antiseptic properties when applied topically. Aboriginal people have long used these oils to heal wounds and fungal infections and they also found a place in traditional Indian, Chinese, Greek and European medicine. To this day eucalyptus oil is still a popular remedy in chest rubs and decongestants designed to treat coughs, colds, chest infections and sinusitis.

According to the University of Maryland Medical Center, laboratory studies have proven that eucalyptus oil contains anti-bacterial substances. Currently, other studies are under way to investigate whether eucalyptus also has the ability to kill fungi and/or viruses. However, if eucalyptus did have anti-viral properties, then koalas would not be contracting and dying from the Koala Retrovirus (KoRV), an infection that continues to spread among the koala population. Researchers are feverishly trying to find a treatment because if they are unsuccesful, koalas in Queensland could face extinction.

Over the past few years, various medical journals have investigated eucalyptus oil as an insect repellant. To this day, the most effective insect and mosquito repellent is DEET (N,N-Diethyl-meta-toluamide), developed by the US army in 1946 in order to protect soldiers in war-zone insect-infested areas. Although scientists are not entirely sure how DEET works, the consensus is that DEET somehow manages to confuse the insects exposed to the repellent. And in their confusion, the insects are unable to locate humans or animals.

Dr. James Logan, researcher at the London School of Hygiene and Tropical Medicine, worries that DEET is losing its effectiveness against mosquitos. A study conducted on the mosquito species Aedes aegypti led to some interesting findings. After being sprayed for the first time with DEET, the mosquitos were repelled. Then, a few hours later, when sprayed a second time, the bugs showed tolerance. DEET was no longer functioning as a mosquito repellant. This is bad news because if mosquitos can develop such tolerance, we may be left without an effective repellant.

Fortunately, many scientists have been searching for effective alternative mosquito and insect repellents. This is where eucalyptus becomes important! Another study conducted at the London School of Hygiene and Tropical Medicine revealed that eucalyptus-based natural repellent gave 97% protection for 4 hours, while DEET only gave 85%. In addition, the London School of Hygiene and Tropical Medicine conducted another study to investigate the difference between DEET and eucalyptus-based insect repellent. Both repellants gave complete protection in Tanzania for 6 to 7.75 hours. It appears that in terms of efficacy and duration of protection no significant difference exists between DEET and eucalyptus-based insect repellents. The active ingredient in eucalyptus-based insect repellent has been determined to be p-menthane-3,8-diol (PMD). Various studies confirmed that due to isomeric mixtures, the naturally derived PMD is more effective than the synthetic PMD derivatives. This is one of the rare cases when a natural chemical is preferable over the synthetic version.

All in all, both the Center for Disease Control and FDA approve oil of lemon eucalyptus as a mosquito repellant that can offer protection against the West Nile virus. And perhaps, if you forgot to pack insect repellant, hugging a koala may be an effective alternative to repelling the mosquitos. But watch those claws. They are razor sharp!

Alexandra Pires-Ménard

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