Wild Medicine—Beneficial Diets

Everyday diets include beneficial nonnutritional components. A few of many possible examples are described here.

In the rain forests of Costa Rica, mantled howler monkeys are infested with different quantities of internal parasites, depending on where they live. Those living in La Pacifica have high levels of parasites, and those living in Santa Rosa have low levels. None of the heavily infested group has access to fig trees (Ficus spp), but the less infested group has many fig trees available. South Americans traditionally use fresh fig sap to cure themselves of worms because the sap decomposes worm proteins (Stuart, 1990; Strier, 1993; Glander 1994).

In the Fazenda Montes Claros Park in southeastern Brazil, endangered muriquis (or woolly spider monkeys) and brown howler monkeys are completely free of all intestinal parasites—a startling and unexpected discovery. In another location, both species are infested with at least three species of intestinal parasites. The main difference between monkeys in the two locations is that the worm-free monkeys have access to a greater selection of plants used as anthelmintics by local Amazonian people (Stuart, 1993).

The everyday diet of great apes contributes much to the sustainable control of parasites. Chimpanzees at Mahale Mountains National Park, for example, eat at least 26 plant species that are prescribed in traditional medicine for the treatment of internal parasites or the gastrointestinal upset that they cause (Huffman, 1998).

In Brazil, the gold and red maned wolf roams the forest at night hunting small prey but taking up to 51% of its diet from plants. By far, its favorite is the tomato-like fruit of Lobeira, or Wolf’s fruit (Solanum lycocarpum). Although these fruits are more plentiful at certain times of year, the wolf works hard to eat a constant amount throughout the year, suggesting that this fruit is of some significant value. Researchers at Brazilia Zoo found that they could not help their captive wolves survive infestation with a lethal endemic giant kidney worm unless they fed Lobeira daily to their packs (daSilveira, 1969).

Correlations have been noted too in domestic diets and worm loads. When commercially raised deer in New Zealand were grazed on forage containing tannin-rich plants such as chicory, farmers needed to administer less chemical de-wormer (Hoskin, 1999). Furthermore, given a choice, parasitized deer and lambs select the bitter and astringent Puna chicory, thereby reducing their parasite load (Schreurs, 2002; Scales, 1994). Tannin-rich plants such as this are commonly selected in moderate amounts by free-ranging animals. Researchers in Australia and New Zealand have found that certain types of forage such as Hedysarum coronarium, Lotus corniculatus, and L. pedunculatus, which contain more useful condensed tannins, can increase lactation, wool growth, and live weight gain in sheep, apparently by reducing the detrimental effects of internal parasites (Aerts, 1999; Niezen, 1996). Tannin-rich pastures may also provide opportunities for ungulates to regulate bloat (McMahon, 2000).

Occasionally, even extra large doses of astringent tannins may be consumed. Janzen described how the Asiatic two-horned rhinoceros occasionally eats so much of the tannin-rich bark of the mangrove Ceriops candolleana that its urine turns dark orange. He postulated that the rhinoceros may be self-medicating against endemic dysentery, pointing out that the common antidysentery medicine—clioquinol (Enterovioform)—consists of about 50% tannin (Janzen, 1978).

Adaptive Taste Preferences

Evidence suggests that animals seek out particular tastes because of the adaptive consequences. Tannins usually deter mammals from eating plants because their astringency puckers and dries the tongue and impairs digestion by binding proteins. However, as we have seen, tannins are not avoided entirely. Given a choice, deer avoid selecting food with the lowest tannin levels and instead select those containing moderate amounts, suggesting that a certain amount of tannin is attractive to them (VerheydenTixier, 2000). It appears such taste preferences may be adaptive because of the impact of tannins on intestinal parasites. When domesticated goats were fed polyethylene glycol (PEG), which deactivates tannins, numbers of intestinal parasites increased (Kabasa, 2000). Sheep, goats, and cattle increase tannin consumption when fed the deactivating PEG. Alternatively, when fed high-tannin diets, lambs increase PEG intake (Provenza, 2000). These results indicate an attempt to self-regulate tannin consumption to an optimal level.

As we shall see in the next section, other so-called feeding deterrents are sought out when their potent bioactive effects outweigh taste aversions.

Bioactive Botanicals—Toxin or Medicine?

Chimpanzees have similar taste preferences to humans. They prefer sweet over bitter foods. In the Mahale Mountains of Tanzania is a small shrub, Vernonia amygdalina, known as bitter leaf. Its extreme bitterness successfully keeps most indigenous animals away, although introduced domesticated goats appear unable to identify the risks; consequently, another common name for this plant is “goat killer.” When local chimpanzees are sick, they seek out this bitter, toxic plant, carefully strip off the outer layers of shoots, and chew and suck the juicy bitter pith.

The plant is considered a very strong medicine by local people who use it to treat malarial fever, stomachache, schistosomiasis, amoebic dysentery, and other intestinal parasites (Huffman, 1989). Pig farmers in Uganda supply their animals with branches of this plant, in limited quantities, to treat intestinal parasites.

Bitter pith chewing is rare, but chimpanzees with diarrhea, malaise, and nematode infection recover within 24 hours (similar to the recovery time of local Tongwe people who use this medicine). The behavior clearly influences nodular worm infestation. In one example, fecal egg count dropped from 130 to 15 nodular worm eggs within 20 hours of chewing bitter pith. Bitter pith chewing is more common at the start of the rainy season, when nodular worms increase (Huffman, 1997b) (Figure 2-1). Furthermore, scientists have noticed that 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.

Figure 2-1 Chimpanzee sucks on the bitter pith of Vernonia amygdalina (bitter leaf) in Tanzania.

(Courtesy Michael Huffman.)

Vernonia amygdalina from Mahale contains seven steroid glucosides, as well as four sesquiterpene lactones, capable of killing parasites that cause schistosomiasis, malaria, and leishmaniasis. The sesquiterpene lactones (previously known to chemists as “bitter principles”) are not only anthelmintic but also antiamoebic, antitumor, and antimicrobial. The outer layers of the shoots and leaves of the shrub, which chimpanzees so carefully discard, contain high levels of vernonioside B1 that would be extremely toxic to a chimpanzee. Not only can chimpanzees find a suitable plant to alleviate their symptoms, they can also find the right part of the plant to be effective without harm (Ohigashi, 1991, 1994).

It is possible that bitterness in plants may be an effective indicator of medicinal properties: it generally indicates toxicity, but it is this very toxicity that is so effective against parasites. This plant is not just bitter, it is the most bitter plant the chimpanzees can find in the forest. One slurp of its juice will make an adult human wince. Chimpanzees and other animals normally avoid it, but appetitive or tolerance changes may take place during sickness. Sick human patients will apparently tolerate more bitter herbal prescriptions, but as health improves, their tolerance of bitters declines. The mechanism that brings about these changes is not yet known, but experimental evidence supports the idea of an adaptive taste preference for bitters.

Laboratory mice were used to explore the link between illness and consumption of bitters. Experimental mice were given a choice between two water bottles—one contained only water, and the other, a bitter-tasting chloroquine solution that would combat malarial infection. Control mice were given only water. Those mice infected with malarial parasites and given access to chloroquine experienced significantly less infection and mortality than did infected mice with no access to chloroquine. Malarial infection was reduced because mice took approximately 20% of their water from the bottle containing the bitter chloroquine solution. However, consumption of chloroquine was not related to malarial infection. Given a choice, both sick and nonsick mice took small doses of the bitter solution, supporting the idea of an adaptive taste preference for moderate consumption of bitters (Vitazkova, 2001).

It is not only primates, or even vertebrates, that use herbal medicines to control parasites. Even insects do it. It has long been known that certain butterflies harvest and store the toxic cardiac glycosides from milkweed plants, and that this stash protects them against some predatory birds. However, these glycosides also protect butterfly larvae from internal parasites. It is not clear whether these benefits are merely incidental to feeding, yet the dietary choice is distinctly beneficial.

Scientists who study insect parasitoids (lethal parasites) have found convincing evidence that insects do self-medicate. Woolly bear caterpillars of the tiger moth can be injected with the eggs of parasitic tachinid flies. Fly larvae develop inside the caterpillars, feeding off their fat reserves and finally bursting out of the abdominal wall. Under laboratory conditions, infected caterpillars usually die from this experience. However, when Richard Karban and his colleagues at University of California Davis started rearing their caterpillars in outdoor enclosures, they noticed that the survival rate of parasitized caterpillars was much higher. Outside, the caterpillars had access to plant species not provided in the laboratory. Given a choice, healthy caterpillars chose to feed on lupine (Lupinus arboreus), and parasitized caterpillars preferred to feed on hemlock (Conium maculatum). Having parasites affected dietary choices, and the change in diet improved chances for survival. Although hemlock, which is known to contain at least eight alkaloids, does not kill the parasites, it helps caterpillars survive infection (Karban, 1997).

Geophagy

Geophagy—the consumption of soil, ground-up rock, termite mound earth, clay, and dirt—is extremely common in mammals, birds, reptiles, and invertebrates. The habit is still found among many contemporary indigenous peoples, including the Aboriginal people of Australia and the traditional peoples of East Africa and China (Abrahams, 1996).

Geophagy is far more common in animals that rely predominantly on plant food and is more common in the tropics. Historically, the explanation for geophagy was that animals ate earth for the purpose of gaining minerals, such as salt (sodium chloride), lime (calcium carbonate), copper, iron, or zinc. Certainly, wild animals do seek minerals from natural deposits, but a need for minerals is by no means a universal explanation for geophagy. There are many cases in which the soils eaten are not rich in minerals; they sometimes even have lower levels of minerals than the surrounding topsoil. Recent geophagy research indicates that the small particle clay profile of soil is often the prime reason for geophagy.

In the body, clays can bind mycotoxins (fungal toxins), endotoxins (internal toxins), manmade toxic chemicals, and bacteria, and they can protect the gut lining from corrosion, acting as an antacid and curbing diarrhea. In short, clay is an extremely useful medicine.

The benefits of clay to animal health have been known for some time. Addition of bentonite clay improves food intake, feed conversion efficiency, and absorption patterns in domestic cattle by 10% to 20%. Clay-fed cattle also experience less diarrhea and fewer gastrointestinal ailments (Kruelen, 1985). In addition, veterinarians find clay an effective antacid. Free-ranging cattle help themselves to clay by digging out and licking at subsoils.

High in the Virunga Mountains of Rwanda, mountain gorillas mine yellow volcanic rock from the slopes of Mount Visoke. After loosening small pieces of rock with their teeth, they take small lumps in their powerful leathery hands and grind them to a fine powder before eating (Schaller, 1964). Gorillas are more likely to mine rock in the dry season, when they are forced to change their diet to plants such as bamboo, Lobelia, and Senecio, which contain more toxic plant secondary compounds than are found in their usual diet. Along with this change in diet comes diarrhea (a natural response to rid the body of toxins); this extra loss of fluid during the dry season could be a serious health problem for the gorilla (Fossey, 1983). Halloysite, the type of clay found in the subsoil eaten by mountain gorillas, is similar to kaolinite, the principal ingredient in Kaopectate, the pharmaceutical commonly used to soothe human gastric ailments. Kaolinite helps reduce the symptoms of diarrhea by absorbing fluids within the intestine (Mahaney, 1995).

Wild chimpanzees take regular mouthfuls of termite mound soil and scrape subsoils from exposed cliff faces or river banks. When scientists spent 123 hours looking specifically at the health of chimpanzees eating termite mound soil, they found that all were unwell, with obvious diarrhea and other signs of gastrointestinal upset (Mahaney, 1996). Analyses of termite mound soils show them to be low in calcium and sodium but high in clay (up to 30%), more specifically, in the same sort of clay used by mountain gorillas and sold by human chemists to treat gastrointestinal upsets in the West. Termite mound soils are used not only by chimpanzees but also by many other species, such as giraffes, elephants, monkeys, and rhinoceroses.

In the rain forests of the Central African Republic, forest elephants and other mammals have created large treeless licks on outcrops of ancient subsoils (Figure 2-2). Most are high in minerals, but almost a third of the licks have lower levels of minerals than surrounding soils. The one thing all the sites have in common is a clay content of over 35%. These elephants feed primarily on leaves all year round, except for 1 month—September—when ripening fruit is so abundant that they change to eating mainly fruits. Leaves generally contain defensive secondary compounds to deter herbivores; ripe fruits do not. A change from eating leaves to fruits would therefore dramatically reduce the consumption of toxic secondary compounds—a natural experiment to see whether toxin consumption equates with clay consumption. The only month in which elephants reduce their visits to the clay licks is during that fruit-eating month—September (Klaus, 1998)!

Figure 2-2 Elephants dig down to find clay deposits in Central Africa.

(Courtesy Martin Gruber.)