Zoopharmacognosy : The Self-Medication Behavior of Animals

Zoopharmacognosy : The Self-Medication Behavior of Animals

The science of animal self-medication is called zoopharmacognosy, derived from the roots zoo (“animal”), pharma (“drug”), and gnosy (“knowing”).

It’s not clear how much knowing or learning is involved, but many animals seem to have evolved an innate ability to detect the therapeutic constituents in plants. Animals have an innate ability to self-medicate using plants, clays and other natural remedies, and in the wild they will forage for them at the earliest stages of any health issue.

In captivity, although they have the same innate drives, they do not have the freedom to roam and seek the remedies they need, and by the time they visibly appear unwell or distressed, the issue may have been building for some time.

The term “Zoopharmacognosy” was first coined by Professor Dr. Eloy Rodriguez (Biochemist), Cornell University, USA. However, the idea was initially proposed by Daniel H. Janzen, in 1978 and he compiled all the anecdotal accounts of possible self-medication in animals.

The concept of self-medication in non-human vertebrates was first proposed by Daniel H Janzen (1978), an ecologist at the University of Pennsylvania . He is the first one to compile all the anecdotal accounts of possible self-medicating behaviour in a variety of animals. Janzen argued that energy requirement alone is not sufficient to explain these unusual feeding habits and raised the possibility that animals can use plant secondary metabolites as stimulants, laxatives, antiparasitic and antibiotics or as antidotes for previously consumed toxins. The term ‘zoopharmacognosy’ therefore describes the process by which wild animals select and use specific plants with medicinal properties for the treatment of diseases and protection from parasites. Biologists the world over have now started accepting the concept of animal self-medication after observing many unusual feeding habits exhibited by the animals of their interest. Previously, it was thought that the main selective pressure which would have possibly favored the evolution of foraging behaviour is to get nutrition ally adequate diet. However, it is now recognized that some features of diet selection seems to have evolved to reduce the risks of parasitismand it has been proposed that diet-selection can be shaped such a way as to reduce or control parasites.

By nature, animals are clever and may selectively forage on leaves, stems, roots and algae to maintain their health. In the last few decades scientists discover that these parts of plants have medicinal properties that can cure infections and various diseases.The evident examples of Zoopharmacognosy is the discovery of coffee, which was an accidental observation by a shepherd. He observe that the goat gets stimulation after consuming the berries of wild coffee plants in highlands of Ethopia.The observation of consumption of plants “chota chand” by the mongooses, in foothills of Himalayas before fighting with cobras has led to the discovery of potent antidote of snake-bite, present in their roots.Two types of self-medication in animals exist, one is preventive medication, which is prevention of diseases or parasitic infestation and other is therapeutic medication, which is treatment or cure or disease by self-medication. In case of any injury, the wildlife (animals) rush toward berberis plant, which is multi potent medicinal plant and they either eat berries or suck leaves or barks of berberis plant which is uncommon routinely.

There are a number of questions which are often asked regarding animals’ ability to self-medicate. Self-medication as a behaviour, has developed with animals throughout their entire evolutionary process, but as a scientific field of research it is relatively new.   In-depth research only started in the 1980s, largely initiated by Professor Michael Huffman’s extraordinary observations of a group of wild chimpanzees carefully using different plant parts, in different ways, to address various physical challenges. Although the evidence is entirely circumstantial, the examples are plentiful. The practice is spreading across the animal kingdom in sometimes surprising ways.

Most studies of animal self-medication, however, are in the great apes. In the 1960s, the Japanese anthropologist Toshisada Nishida observed chimpanzees in Tanzania eating aspella leaves, which had no nutritional value. Harvard primatologist Richard Wrangham saw the same behavior at Jane Goodall’s Gombe reserve, where chimps were swallowing leaves whole. Other scientists noted the same in other chimp colonies. Without chewing, the animals weren’t getting much nutritional benefit. So why do it?

In 1996, biologist Michael Huffman suggested the chimps were self-medicating. Huffman, an American who has worked for years in Japan at the Primate Research Institute at Kyoto University, first saw a parasite-ridden, constipated chimpanzee in Tanzania chew on the leaves of a noxious plant it would normally avoid. By the next day, the chimpanzee was completely recovered .

The plants had bristly leaves, rough to the touch. Huffman theorized the chimps were swallowing the plants to take advantage of that roughness, using the leaves and stems to scour their intestines and rid themselves of parasites. Other researchers observed the same practice among other apes across Africa.Huffman established widely used criteria for judging when an animal is self-medicating. First, the plant eaten cannot be a regular part of the animal’s diet; it is used as medicine not food. Second, the plant must provide little or no nutritional value to the animal. Third, the plant must be consumed during those times of year—for example, the rainy season—when parasites are most likely to cause infections. Fourth, other animals in the group don’t participate. If the activity meets these standards, it is safe to assume the animal is self-medicating, Huffman says. Researchers have observed the practice in 25 regions involving 40 different plants.In general, animal self-medication has been classified into two types: preventive (prophylactic – act of using nature’s medicinal resources without any symptoms of infection or before infection), and curative (therapeutic – act of using nature’s medicinal resources only after infection or illness). According to Huffman and Vitazkova (2007), the study of self-medication is devoted to understanding how animals respond to potential threats to their health and reproductive fitness and how these behaviors are maintained within a population. It is important to take into account 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. Instead, self-medication strategies are survival abilities honed by natural selection (Engel, 2005; HUFFMAN, 2001). The term ‘zoopharmacognosy’, or the animal understanding of drugs, was readily applied to the great apes which appear to show an intention of purpose in their medication. In the beginning, this ethological phenomenon was linked to the eating habits of animals, and so it was considered as the study of the non-nutritional use of plants’ pharmacoactive constituents by animals (Rodríguez; Wrangham, 1993). However, as stated by Engel (2002), it is often difficult to differentiate between behaviors that are nutritional and those that are medicinal, because the separation is ‘artificial’. According to Huffman (1997), the basic premise of zoopharmacognosy is that animals utilize plant secondary compounds or other non-nutritional substances to medicate themselves. Many carnivores, including dogs and cats, will now and again chew a particular plant species. For example, grass-eating stimulates either retching or the rapid expulsion of worms in diarrhea. This behavior, which often puzzles pet owners, may be an attempt to self-medicate against bacteria or perhaps parasites. By following wild animals, especially those that are sick, field biologists have begun to draw up lists of plant species that may have healing properties of pharmaceutical interest (Amaral et al., 1998; Huffman et al., 1998a, 1998b; Beattie ; Erhlich, 2001). Bears, deer, elk, and various carnivores such as coyotes, foxes, and cougars have all been observed to seek out and consume specific plant species, and these observations have been interpreted as the use of medicinal plants by wild animals . Whether or not watching animals will prove to be a useful method of discovering new medicinal plants remains to be seen . It is worth mentioning that folk medicine culture is often alleged to have its roots in observations of animal behavior (Martius , 1939), as many field researches point out that indigenous tribes and early peasants discovered the rudiments of their ethnomedicine in the healing plants sought out by sick animals (Engel, 2002). As Johns and Duquette (1991) say, a pharmacophagous behavior uses non-nutrient components that are inevitably present in the diet in a beneficial way; in certain circumstances, obtaining these benefits becomes the primary reason for ingestion a substance. Chimpanzees, for instance, have been reported to consume several plant species containing sesquiterpene lactones for curative purposes (Robles et al., 1995). These authors have discussed recent in vivo antitumor studies with parthenin (isolated from Parthenium hysterophorus L.) and eupatoriopicrin (the principal sesquiterpene lactone in Eupatorium cannabinum L.), as well as the antiulcer activity of dehydroleucodin (isolated from Kaunia rufescens Lund ex De Candolle), and the cardiotonic activity of helenalin (Arnica montana L.).

Types of zoopharmacognosy

• Dirt medicine or Geophagy/Dirt eating:

The dirt/soil eating as clay or chalk is a common observation in many animals (including herbivores), bats, birds, primates and even in humans. Clay licking behaviour in South American parrots reveals that clay contains kaolin, smectite and mica. The preferred soil in kaolinite results in surpassing or approach pure bentonite in their capacity to bird’s quinine and tannic acid.

South Eastern Peru soil contains calcium and sodium so avian geophagy occurred on it. Sodium helps in detoxification process in birds. It is noticeable in Japanese macaques to ingest 2.9797g/individual/day of soil due to its buffer activity. Yellow stone grizzly bears ingest clay/soil having high concentration of magnesium, potassium and sulphur presenting anti-diarrhoeal property.         

• Anting or Insect medicine

Many birds and animals exposed themselves to the insects particularly ants (anting – bird activity). Rubing crushed ants directly (active anting). Babblers and weavers undergo active anting. Or let them crawl in plumage by lying on ants nests (passive anting).

European jay, crows and waxbills, squirrels and monkeys are the mammals that partake in passive anting. It helps in feather maintenance and soothing skin by secreting formic acid, miticides, insecticides, bactericides, fungicides and supplement for birds preen oil.

Sometimes birds expose themselves to millipedes or lime fruit plant. More than 200 song birds’ species partake in anting process.

• External plant medication or topical application of plants as medicine

The masticated plant materials as leaves and the some insects have been rubbed on body by primates with sole purpose to repel or get rid of ectoparasites. As North American brown bears mix their saliva with Osha roots (bear roots: contain 105 active chemicals as coumarins; a fly repellent, for stomachic and infections etc.) to make a paste for fur rubbing.

Highly toxic materials of millipedes have been rubbed by the Venezuelian Capuchin monkeys on their fur during humid season to avoid insects attack or to treat skin irritation. Anti-microbial foliage of birds in the nests, presenting volatile compounds which act as fly repellent and also inhibit bacterial growth.

• Internal plant medication

The folivorous (leaf eating animals) like Hoatzin have specialized bacteria in their crop to breakdown undigestible leafy plants. So that, these animals use the leaves of plants as treatment materials. Cats when swallow any indigestible compound like hairs they consume grass to get rid of it.

The bacteria present in bird’s gut also neutralize toxic secondary compounds present in the consumed plants.

Another example is Chimpanzees, who use Aspilia leaves (have anti-parasitic, antibacterial and anti-neoplastic properties) un-chewed rolled in oral cavity but and engulfed to treat upset stomach and also in rainy season as anti-parasitic material. Bitter pith (V. amygdalina) chewing and leaf swallowing helps the chimpanzees to treat nematode infestation by self-medication.After chewing bitter pith recovery is evident after 20-24 hours. EPG of O.stephanostomum was found to drop from 130 to 15 in 20 hours. African great Apes utilize plants secondary compounds and non-nutritional substances to control intestinal parasites and to get relief from GIT upsets.Certain varieties of baboons in Ethopia consume leaves and fruits of plant Balanites aegyptica for control of schistosomiasis. Phytochemicals (secondary metabolites) have also been consumed by animals as anti-parasitic medication by various animals.

Plants as stimulants

Zoopharmacognosy is seen in many mamals like Chachma baboons in South Africa. They consume small amounts of leaves of specific plants grouped as Euphories for their stimulant property. Plants of family Solanaceae and Euphorbiaceae are well known for stimulant property. A powerful stimulant Tabernanthe iboga has several indole alkaloids. That’s why, many religious societies of Gabon are using it as aphrodisiac. In 1968 widespread use reported by people of Gorillas, porcupine & bush pig going into wild frenzies after digging up and ingestion of the root this plant.

Reproductive remedies

Females of Muriqui monkeys in Brazil get it to prepare themselves before breeding season. This is due to consuming the leaves from a plant Apuleia leiocarpa (JF Macbr) and Platypodium alegans vog., and the fruits of Enterobium contortisiliquim Morong.

The former two plants contain isoflavonoids, that has properties similar to estrogen. Thus decrease fertility, and latter plant, carries a compound known as stigmasterol which is precursor of progesterone that increases the chance of conception. African elephant (Loxodonta Africana) consumes the leaves of tree Branginaceae to induce labor. Pregnant lemurs eat tamarind and barks to boost milk production.

How Zoopharmacognosy can acquire by next generation

Most interestingly, infants imitate their mothers when they feed on specific medicinal plants when they are ill. Ill animals consume certain items other than their natural food, if feel relieved they will then utilize that item in future.

Our early ancestors were always taking medicinal plants like Aspilia and Berberis. That’s why today we eat medicinal plants as our ancestor’s physiology has adapted to eating these plants. The research pertaining to animal’s self-medication also applies to human being or vice versa. Co-evolution of host and parasite has resulted in biological methods to decrease the parasitic infection due to adaptations to physiological immune responses.

Further exploration in the field of zoopharmacognosy would teach us more about behavior, botany, and medicine, all areas in which we may apply our knowledge to benefit future generations – but without wildlife or habitats, there will be little to study (Biser, 2006). Three of the greatest constraints on field investigations of self-medicative behavior are 1) the unpredictability of the behaviors’ occurrence, 2) unreliability of being able to consistently follow and observe sick individuals over time, and 3) restraints on experimental manipulation (Huffman, 1997). As Huffman (2003) stands out, “Phytochemical studies have demonstrated a wide array of biologically-active properties in this medicinal plant species. In light of the growing resistance of parasites and pathogens to synthetic drugs, the study of animal self- -medication and ethno-medicine offers a novel line of investigation to provide ecologically-sound methods for the treatment of parasites using plant-based medicines in populations and their livestock living in the tropics”.

Various source materials used by animals for self-medication

Parasitism: A Prime Selective Pressure

In addition to competition and predation, one of the important biotic stresses in animal societies is the problems associated with parasites, either external or internal in origin. Though parasites often coexist with their hosts without causing considerable deleterious effects, they can be opportunistic also, and can quickly increase in number and overwhelm a host weakened by other forms of stress such as malnutrition or reproduction. Mammals and birds are often exposed to a diverse array of parasites and infectious diseases, many of which affect host survival and reproductive fitness . In a variety of animal hosts, it has been evidently shown that the problems associated with parasites are undoubtedly costly to manage. Parasites can weaken the host’s immune system by either of the two following ways: the haematophagous parasites directly reduce host fitness by continuously sucking blood and nutrients from the body, or parasites can be reservoirs for many deadly transmittable diseases and can act as disease carriers (vectors) among host populations. Thus, parasites can affect host fitness and may eventually have an influence on the evolution of overall life history strategies in animal societies. Therefore, one of the main selective pressures which would have led the animals to use medicinal plants is believed to be parasitic pressure . To overcome the fitness loss due to parasitism, animals have evolved a variety of anatomical, physiological and behavioural adaptations. In addition to the immunological defence, avoidance and removal of parasites are the two behavioural strategies animals useto reduce parasites. Otherbehavioural adaptations evolved against parasites may also include the avoidance of food materials which are potential sources of parasites, the use of prophylactic substances and the consumption of therapeutic substances . In general, animal self-medication has been categorized into two types – preventative (prophylactic – act of using medicinal plants without any symptoms of infection or before infection) and curative (therapeutic – act of using medicinal plants only after infection or illness).

Phytochemicals as Natural Medicine

Plants produce a variety of secondary metabolites which supposedly do not have any obvious role in further metabolism . Secondary metabolites are produced and stored in various parts of the plant (mainly in peripheral regions) (Box 2). Previously, it was thought that the secondary metabolites are the waste products of primary metabolism and are stored in cells because of the absence of an efficient excretory system. However, later it has been recognized that these secondary metabolites are part of plant’s defense mechanism (chemical defense) to deter insects and herbivores from feeding on them, to protect from disease causing microorganisms and to attract the beneficiary organisms which are crucial for their propagation, namely pollinators and seed dispersers . Recently, it has also been recognized that synthesizing these compounds are certainly costly for the plants. It has also been presumed that animals using plant secondary metabolites can also protect themselves from parasites and diseases .

Plants as Stimulants

Chacma baboons (Papio ursinus) in South Africa are known to consume each day a little quantity of leaves of specific plants, which are well known for their stimulant property. The plants were found available throughout the day and their availability is not limited, but baboons were found to feed on them occasionally and only in small quantities. These plants were not classified under baboon’s regular diet, instead, are grouped as ‘euphorics’. The consumption of such plants is not directly related to any illness or a diseased state but shows stimulant activity. These include Croton megalobotrys (Euphorbiaceae), Euphorbia avasmontana (Euphorbiaceae), Datura innoxia and D. stramonium (Solanaceae) . However, there is still no empirical study reporting the plant’s specific pharmacological benefits .

 Antischistosomal Drug Use by Baboons

The anubis baboons (Papio anubis) and hamadryas baboons (Papio hamadryas) in Ethiopia use fruits and leaves of Balanites aegyptica to control schistosomiasis1 . The Awash River valley in Ethiopia is separated into two distinct habitats by the waterfalls, one up in the hills where the water flows rapidly and the second is located at the lower part of the hills, where the water flow is gentle. Though the baboon population and the plant B. aegyptica are distributed in both habitats, the baboons only in the lower part of the valley were observed to feed on the plant and interestingly the population in the lower valley had higher infestation of the parasite. The only difference between these two distinct habitats is a species of snail (Biomphalaria sp.), an intermediate host for the development of schistosoma sp., found downstream of the river valley. B. aegyptica fruits contain diosgenin, a hormone precursor which presumably hinders the development of schistosomes .

External Application of Substances to the Body

‘Anting’ is a behaviour in which birds rub crushed ants throughout their plumage and some birds let the ants to crawl over their plumage by directly lying on ant nests. Anting is reported in more than 200 species of songbirds and it has been suggested that it is used to soothe irritated skin, help with feather maintenance and repel or reduce ectoparasites. The most commonly used ants by birds for anting are those species which contain formic acid. Subsequent empirical studies with bird lice revealed that formic acid is harmful to feather lice . Birds have also been observed anting with other invertebrates like millipedes, plant parts such as lime fruits and inanimate objects like mothballs (napthalene), all of which have some antiparasitic property. Though anting was primarily reported in birds, recently similar behaviour has also been observed in some mammals. ‘Fur rubbing’ is a typical behaviour of rubbing masticated plant materials and other objects such as insects on the external surface of the body by animals. In Costa Rica, it was observed that the Capuchin monkeys (Cebus capucinus) rub their fur with several species of Citrus fruits (Rutaceae) and leaves and stems of Piper marginatum and Clematis dioica (Ranunculaceae) . Fur rubbing has been reported in a variety of primates, like Cebus capucinus,C. olivaceus, C. paella, Ateles geoffroyi, A. belzebuth, Aotus boliviensis, A. lemurinus griseimembra, A. nancymaae and Eulemur macaco . It has been suggested that fur rubbing serves to repel or kill ectoparasites In Venezuela, capuchin monkeys (Figure 1) rub highly toxic millipede secretions into their fur during the humid wet season when insect bites are high. The millipede secretions contain benzoquinones, which are well known for their insect repellent property [9]. White-nosed coatis (Nasus narica) have been observed coating their body with the resin of Trattinnickia aspera (Burseraceae) . This may also serve to control ectoparasites2 and thus should be considered as self-medication .

Inclusion of Antimicrobial Foliage Inside Nests

To date, at least 50 species of birds are known to include fresh plant materials inside their roosting environment that does not constitute as a part of their nest structure. So far, a number of hypotheses have been proposed for this peculiar behaviour. It was noted that the included plants are rich in volatile secondary compounds and hypothesized that birds should be using these plants to repel or kill ectoparasites . Subsequent empirical tests have shown that the preferred plants are effective in reducing the hatching success of bird lice (Menacanthussp.) and also inhibit the bacterial growth. The leaves of wild carrot (Daucus carota, Umbelliferae), a preferred species, significantly reduces the number of fowl mites (Ornithonysus sylviarum) in starling nests . The dusky-footed wood rats (Neotoma fuscipes) place bay foliage around their sleeping nests and it has been experimentally shown that the inclusion of bay foliage significantly reduces the flea larval survival . The wood ants, Formica paralugubris often incorporate large quantities of solidified conifer resin into their nests. By creating resin-free and resin-rich experimental nests, it was demonstrated that the included resin inhibits the growth of pathogenic microorganisms inside ant nests .

Consumption of Medicinal Plants by Animals

In 1987, in the Mahale mountains in Tanzania, self-medication by chimpanzee was observed and first documented by Michael Huffman, a primatologist from the Kyoto University, Japan. His work was the first to show that illness in an animal showed improvement after eating a known medicinal plant Vernonia amygdalina (Compositae) commonly known as bitter-leaf, a best known example for therapeutic self-medication . The sick chimpanzees alone were found to chew the leaves of this shrub. It was later discovered that the plant is 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. Further phytochemical analysis revealed that the bitter pith of V. amygdalina contains seven steroid glucosides, as well as four known sesquiterpene lactones, capable of killing parasites that cause schistosomiasis, malaria and leishmaniasis. The sesquiterpene lactones are antihelminthic4 , antiamoebic, antitumor and antimicrobial . Chimpanzees at the Gombe National Park and Mahale mountains, Tanzania were observed to swallow the whole leaf of Aspilia pluriseta, A. rudis and A. mossambicencis (Compositae). So far, many hypotheses have been proposed for Aspilia sp. consumption. Phytochemical analysis of the leaves has not shown any convincing evidence for pharmacological benefits. However, recent studies suggest that Aspilia sp. may not be consumed because of its phytochemical properties but because of their rough surfaces, which may aid in the mechanical removal of intestinal parasites .

Consumption of Soil and Rock by Animals (Geophagy)

‘Geophagy’ is an act of deliberately consuming soil, stones and rock by herbivorous and omnivorous mammals, birds, reptiles, and insects. This behaviour is observed and studied in the context of self-medication in Japanese macaques (Macaca fuscata), rhesus macaques (Macaca mulatta), mountain gorillas (Gorilla gorilla), chimpanzees (Pan troglodytes) and African elephants. Geophagy is suggested as a means to maintain gut pH, to meet nutritional requirement for trace minerals, to satisfy specific hunger for sodium, to detoxify previously consumed plant secondary metabolites and to combat intestinal problems like diarrhea. Soil analyses indicated the presence of three mineralogically similar clays: halloysite, metahalloysite and kaolinite. Interestingly kaolinite is the principal ingredient in the commercially available antidiarrheal formulate Kaopectate.

In general, the mechanism underlying the selection by animals of specific plants during illness is still unclear. However, it seems that the selection of medicinal plants by an animal involves a fairly complex mechanism of individual and social learning. While taking into account that the costs associated with parasites and diseases, it is likely that almost every organism should have developed many forms of behavioural adaptations against parasites, including self-medication with plant secondary metabolites. Because of the adaptive significance of self-medication, its existence is probably widespread. To recognize this, constant field monitoring and subsequent empirical studies into the selfmedicative behavior of wild animals are certainly essential. Though, it remains difficult to demarcate self-medicating behaviour and many unusual feeding habits of wild animals from the usual foraging activity, the complexity of animals, parasites, plants and their interactions cannot be denied. Studying these interactions in the framework of self-medication may provide an entirely new and novel level to our understanding of animal behavioural ecology.

DR BB OJHA, PRAVARANVID,PUNE

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