I found this very interesting

Scott Buchanan
[email protected]
April 12, 2002
EN 570

Zoopharmacognosy: Animal Self-Medication

Abstract

Not all pharmacists are human; other species also use medicinal substances to combat pathogens and other parasites. Self-medicating behavior is a topic of rapidly growing interest to behaviorists, parasitologists, ethnobotanists, chemical ecologists, conservationists, and physicians. The term â??zoopharmacognosyâ?? was coined to describe the process by which wild animals select and use specific plants with medicinal properties for the treatment and prevention of disease. Although most of the pertinent literature is anecdotal, several recent studies have shown that animals use various natural substances for self-medication and have now attempted to test the adaptive function of particular self-medicating behaviors. Early studies of zoopharmacognosy focused on the interactions between plants and the herbivores that consume them. However, although the potential plant pharmacy is vast, it is not the only source of natural medicines available to animals. Because many insects harvest plant secondary compounds or make their own defensive compounds, they too are a source of potential medicines for other animals. Some chemicals of plant primary metabolism can also affect animal health; even plant structural compounds, such as the fiber found in bark or certain grasses, can be beneficial to those consuming them. Furthermore, therapeutic compounds need not be confined to living material. Soil often contains microbial organisms that themselves secrete bioactive compounds. The study of animal self-medication and ethno-medicinal practices may provide important leads to future sources of medicine. A closer look into the manner in which animals use natural plant products may, for example, provide novel insights into viable new strategies for suppressing or slowing down the rate of acquisition of chemo-resistance by parasites that infect wild animals and humans.

Introduction

Many of us have seen our pet dogs and cats eat grass. Why? Surprisingly there has been no published research of this behavior, but scientists have recorded that eating grass stimulates either retching or the rapid expulsion of worms in diarrhea (Hart and Hart 1985). This may therefore be one aspect of animal self-medication with which we are most familiar. Scientists from various disciplines are currently exploring the possibility that many species use plants, soils, insects, and fungi as 'medicines' in ways that guard against future illness (preventive medicine) and/or relieve unpleasant symptoms (curative or therapeutic medicine).
It is important to note that the scientific study of animal self-medication is not based on an assumption that animals possess an innate 'wisdom' by which they flawlessly know what is good for them. Self-medication strategies are survival skills honed by natural selection. In most cases self-medication could be motivated by a desire to immediately reduce unpleasant sensations. Some species, particularly great apes, show an intention of purpose in their medication and in these cases the term â??zoopharmacognosyâ?? was coined to describe the process by which wild animals select and use specific plants with medicinal properties for the treatment and prevention of disease (Rodriguez and Wrangham 1993).
Since ancient times people have recorded observations of animals apparently healing themselves with natural medicines. Many herbs still retain a common name that infers this use: dog-grass (Agropyron repens), catnip (Nepeta cataria), and horny goat weed (Epimedium sp.), to name a few. However, these observations remain largely unexplored by science. Many stories of animal self-medication are clearly designed to inform and communicate herbal lore rather than fact. Others are simply misinterpretations of animal behavior.
According to Chinese folklore, many centuries ago a farmer in the Yunnan district found a snake near his hut. Fearful for his life, he beat it senseless with a hoe and left it for dead. A few days later, the same snake returned. Again he tried to kill it, but again it returned. After he had beaten it a third time, the farmer followed the severely wounded snake as it crawled into a clump of weeds, started feeding on them, and thereby rapidly cured the worst of its injuries. The plant in the story was Panex notoginseng, which now forms the main ingredient in the herbal formulation 'Yunnan bai yao', a white powder that cauterizes cuts and stems external bleeding immediately. It was standard issue in the Vietnam War, for use when soldiers were wounded far from conventional medical treatment. (Reid 1987).

First documentation of zoopharmacognosy

Rumors of wild chimpanzees practicing curative self-medication in Gombe National Park, Tanzania, have persisted for several decades. It was reported back in the 1970s that chimpanzees were using certain leaves in 'non-nutritional' ways indicative of self-medicative behavior. Over the next two decades, it was established that the chimpanzees were swallowing these leaves as mechanical scours to expel intestinal worms (Wrangham 1995).
In 1987, in the Mahale Mountains, another aspect of chimpanzee self-medication was observed and documented by scientists (Huffman and Seifu 1989). At the beginning of the rainy season, chimpanzees were observed quietly plucking out the red wax-membrane coated seeds of Lulumasia (a relative of nutmeg) from their yellow husks. One of the females was clearly unwell, and slept while the others fed. When awake she moved slowly and reluctantly, ignoring the pleadings of her young son (that normally would have her rushing to his aid). It was noted that her urine was dark and discolored, her stools loose, and her back quite stiff. She was followed to a small shrub, Vernonia amygdalana, commonly known as bitter-leaf. The extreme bitterness successfully warns most animals to stay away. But this sick chimpanzee bent down several shoots of bitter-leaf and carefully stripped off the outer layers to reveal the inner pith that she chewed and sucked for at least 20 minutes and spit out the unwanted fibrous husks. She continued to suck on the bitter-leaf pith while other healthy chimpanzees ate far more nutritious and palatable plants. Her son begged, as usual, for some of what she was eating, but she ignored him. Eventually he got hold of a piece she had dropped and eagerly put it to his mouth, but quickly spat it out in obvious disgust. For the remainder of the day the ill chimpanzee took frequent long naps, eventually making a night nest unusually early. The next morning she was still visibly weak, frequently stopping to rest or sit still, but after a long mid-day nap she appeared to be on the mend - traveling swiftly through the dense forest, she left the rest of the group far behind. She even regained her appetite and she was observed feeding on elephant grass.
It was later discovered that the plant was a very strong medicine for local people. African herbalists often prescribe this plant to treat malarial fever, schistosomiasis, amoebic dysentery and other intestinal parasites and stomach disorders. Later analysis of plants collected at Mahale reveal that the bitter pith of Vernonia amygdalina contains seven entirely new steroid glucosides, as well as four known sesquiterpene lactones, capable of killing parasites that cause schistosomiasis, malaria and leishmaniasis - any one of which could cause the symptoms seen in the ill chimpanzee. The sesquiterpene lactones are antihelminthic, antiamoebic, antitumor and antimicrobial. The leaves and outer bark of Vernonia amygdalina, which were so carefully discarded, contains such high levels of vernonioside B1 that it would have been extremely toxic to a chimpanzee (Huffman and Seifu 1989). It seems that not only had she picked the right plant to deal with her symptoms, she had found the right part of the plant to be effective without being harmful to her.
On another occasion, scientists saw four other chimpanzees (all with diarrhea, malaise and nematode infection) chewing bitter-pith. Two of these individuals recovered within 24 hours (similar to the recovery time of local humans using this medicine). The behavior clearly has an impact on nodule worm infestation. In one case, the fecal egg count dropped from 130 to 15 nodular worm eggs within 20 hours of chewing bitter-pith. In each case, chimpanzees took a detour from their normal feeding forays to find bitter-pith plants (Huffman 1997). Bitter-pith chewing is more common at the start of the rainy season when the presence of nodular worms increase and chimpanzees with higher worm loads, or those that appear to be more ill tend to chew more bitter-pith than those with lower infestation levels (Huffman 1997).

Dirt as Medicine

Many species of mammals, birds, reptiles, and even insects, in all parts of the world, eat dirt. Known as â??geophagyâ??, this behavior has long been assumed to be an attempt to rectify mineral deficiencies in their diet (Johns and Duquette 1991). However, new evidence suggests that this is not always the case. It has become apparent that the clay content is often the most important ingredient of selected soils. In Venezuela free-ranging cattle have been seen digging and licking at clay subsoils (Kruelen 1985). Chimpanzees, giraffes, elephants, and rhinoceroses eat regular mouthfuls of clay-rich termite mound soil and gorillas mine clay-rich volcanic rock from under the exposed roots of ancient trees (Krishnamani and Mahaney 2000, Klaus et al 1998, Houston et al 2001). Clay is an effective binding agent as its chemical structure allows other chemicals to bond with it and thus lose their reactivity. Clay is an effective deactivator of toxins from diet or pathogens and is the primary ingredient of the kaolin found in many over-the counter treatments for gastrointestinal malaise in humans.
In the rain forests of New Guinea, parrots, pigeons and crows were observed flying down to a new landslide of earth and eating the bare dirt. The birds flocked to this rare opportunity to access bare earth in an area densely covered with vegetation. Not all of the observed 140 bird species came down to eat earth, only the eight herbivorous species that regularly ate fruit, seeds and flowers (Diamond 1998). Plants naturally contain numerous toxins that protect them from predators and pathogens. When the landslide soils were analyzed they were found to contain less minerals than the surrounding top soil but the clay content was high and found to be more effective at binding alkaloids and tannins than pure pharmaceutical kaolinite (Diamond 1998). This suggests that these birds were taking advantage of newly disturbed earth and selecting soil of just the right properties to bind and deactivate plant toxins.

Insects as Medicine

Many insects synthesize defensive toxins or take toxins from their diet to store in their bodies where they deter predators and combat infection and parasites. They may therefore contain strong bioactive compounds that are potentially medicinal to other animals. At least 73 insects are listed as medicinal in Chinese medical texts (Reid 1987).
More than 200 species of songbirds wipe ants through their plumage (Moyer and Clayton 2001). During this 'anting' behavior, birds take an ant in their bill and wipe it vigorously along the spine of each feather down to the base. Birds may also roll in anthills twisting and turning to allow the ants to crawl through their feathers. The ants birds most commonly use in this way are those that spray formic acid. In laboratory tests formic acid is damaging to feather lice and its vapor alone is enough to kill the lice (Clayton and Wolfe 1993). The medicinal benefits of formic acid have not escaped the attention of beekeepers around the world, which use it to control parasitic mites of honeybees (Kochansky and Shimanuki 1999).
Although anting was first recorded in birds, ant nests are also sought by squirrels, cats, and monkeys who roll in them for similar relief (Hauser 1964, Longino 1984). In Venezuela wedge-capped capuchin monkeys rub highly toxic millipede secretions into their fur during the humid wet season when insect bites (particularly mosquito bites) are ferociously high. The insect secretions contain benzoquinones, which are powerful insect repellents (Valderrama et al 2000).

Plants as medicine

Plants synthesize many defensive compounds to protect themselves from disease and predators. These compounds are bioactive and can be medicinal, intoxicating or toxic depending on circumstances. Many insects are pharmacophagous - that is, they eat non-nutritive substances that may serve as 'drugs'. One benefit the insects gain by eating plant toxins is protection from predators, fungi, bacteria and parasites. For example, when infested with internal parasites, the woolly caterpillar switches to eating highly toxic hemlock and its chances of surviving the normally lethal parasite infestation increase significantly (Karban and English-Loeb 1997)
Many birds bring fresh green plant material to their nests, during nesting, and continue to replace and replenish it, as though freshness were important. Male European starlings in North America carefully select certain species, preferring in particular, wild carrot (Daucus carota), yarrow (Achillea millefolia), agrimony (Agrimonia paraflora), elm-leaved and rough golden rod (Soldiago sp), and fleabane (Erigeron sp), even though these may not be the most common plants nearby (Clark and Mason 1985). The plants they choose are highly aromatic. They also contain more volatile oils and in greater concentrations than aromatic plants nearby that are not selected. When fresh plants are removed from starling nests in the field, chicks in these nests suffered greater mite infestations than those in which the herbs remained. Furthermore, chicks in nests containing wild carrot had higher hemoglobin levels than those in nests without it - presumably because they were losing less blood to the blood-sucking mites (Clark and Mason 1988). If starling-selected plants are placed in a plastic bag with nesting material, mite larvae emergence is delayed. Other available aromatic plants that are ignored by starlings do not have this effect on mites. The preferred plants contain monoterpenes and sesquiterpenes that are harmful to bacteria, mites and lice in the laboratory (Clark and Mason 1985). In particular, they are effective against the bacteria Streptococcus aurealis, Staphylococcus epidermis and Psuedomonas aeruginosa but not against the common usually harmless Escherichia coli. Although the plants retard the hatching of louse (Menacanthus) eggs, and the emergence of mite (Ornithosyssus sylvarium) larvae, they do not kill either adult lice or adult northern fowl mites (Fauth et al 1991).
Starlings have a good sense of smell and choose the most aromatic of all the available plants. Their ability to detect these volatile oils varies seasonally, being most acute at the time of reproduction when medication is so important (Clark and Mason 1985). Starlings are able to discriminate between a preferred plant (wild carrot) and a less preferred plant (red dead nettle) in April (at the beginning of breeding season) but not in September (outside the breeding season). This suggests that the seasonal changes in male testosterone levels influence their ability to detect these important plant odors (Clark and Mason 1987).
The plants chosen by starlings are plants also commonly used externally by herbalists for skin problems such as ulcers, sores and eczema. This is interesting because instead of looking solely for direct impacts on ectoparasites, it may be important to determine whether birds are selecting plants whose volatile chemicals help with the symptoms of ectoparasite infestation; namely scabs, sores and itches (Engel 2002). Recent research confirms that symptoms are indeed the main focus of starling nest medication. It has been found that starlings bring different leaves to the nest in Europe and that these leaves do not harm ectoparasites at all. Nestlings in herb nests have greater mass and higher blood iron levels at fledging than those in grass nests. More yearlings from herb nests are also seen the year after hatching indicating that the herbs in these nests are enhancing the health of the chicks directly, "helping them to cope better with the harmful activities of ectoparasites" (Gwinner et al 2000).
Wood storks also reuse old nests, often for generations, over many decades and also bring fresh green material to their nests. Many of the plants they use are also highly volatile such as red cedar (Juniperus silicola), cypress (Taxodium distichium), black gum (Nyssa bioflora), poison ivy (Toxicodendron radicans), red maple (Acer rubrum), wax myrtle (Myrica cerifera), Virginia creeper (Parthenocissus quinquefolia), and water oak (Quercus virginiana). When tested against large skin beetles that infest wood storks, these plants had no effect. However, wood storks' selections show the same profile of aromatic, bitter and astringent plants, suggesting that medication may be about treating the symptoms of mites and bites rather than impacting directly on the ectoparasites (Rodgers et al 1988).
The domestic house sparrow is in on the act too. In Calcutta, scientists have noticed that the house sparrow usually brings neem (Azidiachta indica) leaves, which are powerful insecticides, to line its nest at hatching time. These sparrows have also been observed to change from neem to quinine-rich leaves of Krishnachua tree (Caesalpinia pulcherrima) during an outbreak of malaria. Quinine controls the symptoms of malaria and scientists wonder whether the sparrows were selecting leaves to deal with malarial symptoms (Senegupta and Shrilata 1997).

Mechanical Scours

The ease at which animal observations can be misinterpreted and a caveat for future studies of zoopharmacognosy is illustrated by the case of leaf swallowing by chimpanzees in Gombe. In July 1972, Richard Wrangham noticed a wild chimpanzee feeding in a strange manner. Aspilia spp. leaves were selected slowly and carefully, unlike normal feeding when bunches of leaves were greedily stuffed into the mouth. Furthermore, they seemed to be kept in the mouth for some time before being swallowed. It was obvious that the leaves weren't palatable because often the chimpanzees wrinkled their noses as they swallowed them and, when he tried some himself, he found out why. They were rough, sharp and "extremely nasty to eat" (Wrangham and Goodall 1989).
Japanese primatologists have observed similar behavior in the Mahale Mountains, south of Gombe. Aspilia did not form part of the chimpanzee normal diet yet they went out of their way to find the leaves. Chimpanzees lick, taste and hold a young leaf on it's tongue for a while often while still attached to the plant, then perhaps abandons that leaf and tries another one. When a leaf is finally selected it is then folded and held in the mouth for a few seconds before being swallowed whole. Later, the undigested leaves re-emerge in the feces. Feces contain undigested leaves far more often in the rainy season (November to March) than in the dry season; and females swallow leaves significantly more than males do (Newton and Nishida 1990).
Aspilia plants are commonly used in traditional African medicine for treating upset stomach and coughs, and when Aspilia mossambicensis leaves collected from Mahale were analyzed, the results showed that they contained the chemical, thiarubrin-A. Thiarubrins had been discovered recently in other plants and were known to be antibacterial, antifungal and anthelmintic. From this researchers inferred a similar property for the leaf swallowing by chimpanzees (Rodriguez et al 1985).
Chimpanzees carry an assortment of nematodes and these are more common at the beginning of the rainy season when chimpanzees are known to swallow more leaves. The seasonal correlation suggested that something in the leaves - possibly thiarubrines - was being used to combat nematodes. However, a study that meticulously replicated the chemical analyses of Aspilia mossambicensis could only find small traces of thiarubrine in roots, and none in the leaves (Page et al 1997). The evidence for a chemical basis to leaf swallowing was receding.
Chimpanzees across Africa had been seen swallowing the leaves of 19 different species of plants, from widely different plant groups, containing an array of compounds with varying medicinal actions, many of which had no effect on internal parasites at all. It became increasingly evident to researchers that the only thing these leaves had in common was their rough texture (Messer and Wrangham 1995). When freshly excreted swallowed leaves were examined found nodule worms, alive and wriggling, attached to tiny barbs on the leaf surface (Huffman et al 1996). The leaves physically scrape worms through the gut. The careful folding of the leaves is thought to increase the chances of hooking worms as they wriggle and become trapped in the folds (Huffman 1997).
Leaf swallowing has now been seen in at least eleven different populations of chimpanzees, as well as in eastern lowland gorillas, in at least ten different sites across Africa. The great apes swallow a variety of leaves from 34 species of herbs, trees, vines, shrubs; some of the leaves contain bioactive chemicals, others do not, but all are rough in surface texture with hook-like microstructures called trichomes (Huffman 2001).
Leaf swallowing is seen mostly at the beginning of the rainy season when nodular worm infestation starts to increase and apes can swallow from one to a hundred leaves in one bout. Many leaf-swallowing apes are clearly suffering from the symptoms of nodule worm infestation: diarrhea, malaise, and abdominal pain. Mechanical expulsion (scouring) could be particularly effective at reducing nodule worm infestation as they move around freely in the large intestine looking for food and mates and have no permanent attachment to the intestinal wall (Huffman 2001). Other worms (such as thread worms and whip worms) burrow into the mucosa of the small intestine and so probably escape the scraping effects of rough leaves. However, it has been found that leaf swallowing helped chimpanzees at Kibale National Park, Uganda, rid themselves of a particularly heavy outbreak of tapeworms (Bertiella studeri) (Wrangham 1995).
In addition to hooking loose worms, the rough leaves stimulate diarrhea and increases gut motility, which also help shed worms and possibly their toxins from the body (Huffman and Caton 2001). Furthermore, when adult worms are removed from the gut, larvae emerge from the tissues thereby rapidly relieving more general feelings of malaise. It is this rapid relief that most likely motivates leaf swallowing 'self-medication' behavior (Huffman and Caton 2001).

Conclusions

Further field and laboratory research into the self-medicative behavior of wild animals is definitely needed. As this review has shown, answers to a few questions invariably lead to more questions. As more researchers in the field begin to look for similar types of behavior, they will be found and more answers. Because of the obvious adaptive significance of self-medication, its existence is probably widespread. The challenge is in finding what immediate threats to health and survival are in a population and by what means they are dealt with by that particular species.
Whether it be chimpanzees selectively ingesting plants in ways that lead to the seasonal expulsion of certain parasites, the use of clay as a treatment for gastrointestinal distress, or the antng behavior of some bird species, the complexity of animal, parasite, and plant interactions cannot be denied. Study of these interactions in the framework of self-medication may provide a new and entirely novel level of complexity to our understanding of animal behavioral ecology.

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