Exploring the Antiparasitic Activity of Medicinal Plants

Parasitic disease is one of the major public health problems affecting hundreds of millions of people. Worldwide, more than three billion cases of parasitic disease are reported yearly. The parasites have sometimes become resistant to the available synthetic therapeutics, so it is important to search for alternative sources of anti-parasitic drugs. Plants contain different phytoconstituents with different biological activities. Many previous researches showed that many plants exerted antiparasitic activity due to its secondary metabolites. This review highlights the antiparasitic effects of different medicinal plants and to know the mode of action of different phytochemicals against parasites.


INTRODUCTION
Parasitic diseases are the most important public health problem impacting a large number of people worldwide. Parasites are considered to be a major problem in our life. A large variety of parasites have developed during the evolution of humans. Typically, a parasite will not destroy its host instantly. Most internal parasites are weakening our health, while think of lice and fleas are unpleasant for us. If the patients do not get appropriate therapy, some parasitic infections can be deadly, such as Chagas, trypanosomiasis or malaria 1 . The transmission of parasites is facilitated because of the badhygienic conditions. People have often tried to mitigate the parasitic infection. Mechanically, it may minimize or eliminate external parasites. While, internal parasites are more complicated to treat 2 . A number of drugs have been synthesized from the medicinal chemists which can be used as antiparasitic drugs, but some parasites showed resistance to these drugs. So, searching for antiparasitic drugs from natural origin is necessary to be an alternative to synthetic drugs 3  are known as one of the most common infections 8 . The lives of billions of people worldwide are affected by protozoan parasites that cause large economic impacts 9 .

Types of parasites
There are two main types of parasites endoparasites and ectoparasites. Human endoparasites live inside their hosts, in the alimentary canal or within cells or tissues. There are two types of endoparasites; Protozoa which include the unicellular organism called Plasmodium. The other type are helminthes (worm parasites) such as; tapeworm, fluke, pinworm, roundworm and trichina spiralis. On the other hand, ectoparasites live on, rather than in their hosts. They include fleas and lice 10 .

Prevention
To avoid and prevent parasitic infections, there are several precaution should be followed such as; washing the hands regularly, drink clean water and avoid swallowing water from ponds streams or lakes, cook food to its recommended internal temperature, avoid cat feces and litter especially for pregnant woman and safe sex practicing 11 . Diagnosis There are different ways for diagnosis of the parasitic infections such as; a blood test, a fecal exam to check the presence of parasites or their eggs in the stool sample, colonoscopy or endoscopy in which the doctor will pass a thin tube into the digestive system through the mouth or rectum of patient to examine his intestinal tract, the other ways for the diagnosis of parasitic infections by some scans to inspect the presence of any lesions or damages of organs by parasites, these scans such as; magnetic resonance imaging (MRI), computerized axial tomography (CAT), or X-ray 11 . Treatment A number of drugs have been synthesized from the medicinal chemists that can be used as antiparasitic drugs. Some parasites showed resistance to these drugs. So, searching for antiparasitic drugs from natural origin is necessary to be used instead of synthetic drugs 3 . For the pharmaceutical industry, the production of new synthetic antiparasitic drugs is a risky affair due to a high price of the drugs and because a lot of parasitic infestations exist in developing countries where it is difficult for the people to pay. So, new drugs derived from natural products or their derivatives are necessary to be an alternative to synthetic drugs 2 . Natural products play a vital role in medicine; large numbers of new drugs were derived from natural products or their derivatives 4 . Table 1 showed examples of some anthelmintic drugs.  Uncoupling the oxidative phosphorylation leads to disturbance in energy generation mechanism Alkaloids

13, 24
-At as an antioxidant -Steroidal alkaloid and oligoglycosides inhibit the transfer of sucrose from the stomach to the small intestine. -Cause paralysis due to its effect on central nervous system. Tannins 5, 25 -Uncoupling the oxidative phosphorylation leads to disturbance in energy generation mechanism -Binding glycoprotein on the cuticles of the worms or the free protein of the GI tract of the host animal Cysteine proteinases 26

Cause digestion of nematode cuticle
Isoflavones 27 Disturb the Ca +2 homeostasis in the parasites. Inhibit the enzymes of glycogenolysis and glycolysis

Zingiber officinale Rosc (Ginger)
Zingiber officinale belongs to family zingiberaceae . Zingiberene, gingerols, shogaols and bisabolene are the main active compounds of Zingiber officinale. A monocyclic sesquiterpene (zingiberene) is the main component of ginger oil. It gives ginger its distinct flavoring and represents about 30% of the essential oils in ginger rhizomes. The alcoholic extract of rhizomes of Z. officinale showed the anthelmintic activity against human A. lumbricoides. Also it exhibited antischistosomal activity 16 .

Dryopterisfilix-mas
Dryopterisfilix-mas (Dryopteridaceae) contains biologically active compounds that effective against cestodes and causing worm muscles paralysis, these compounds (vermicidal phloroglucinols) such as deaspidin, filixic acid and aspidin 2 . Punicagranatum Punicagranatum (Lythraceae) is effective against gastrointestinal nematodes. The crude extracts of P. granatum showed a potential anthelmintic activity. By comparing with the negative control, the extract showed a potent nematocidal effect at the highest concentration (10 mg/ml). Moreover, plant extract showed a potent inhibitory effect against hatching of the egg within 48hr of exposure 13 . Artemisia herba-alba Artemisia herba-alba (Asteraceae family) is used as an anthelmintic agent. The crude extract of A. herba-alba showed a potential anthelmintic activity at all dose levels. Artemisia herba-alba flower extract showed a potent inhibitory effect against egg hatching (98.67%) at concentration 1 mg/ml comparing with the negative control, this result confirmed the nematocidal activity of Artemisia herba-alba 13 .

Ailanthus altissima
Ailanthus altissima belongs to Simaroubaceae family. vitro In addition, the presence of the quassinoidail anthonein the plant plays an important role in this activity 17 .

Allium cepa (onion) and Allium sativum (garlic)
The effects of onion (Allium cepa )and garlic (Allium sativum) on adult parasite Lernantropus kroyeri (L. kroyeri) were studied. Results showed that onion and garlic juices exhibited the inhibitory effect on the females of Lernantropus kroyeri in a concentration and time dependent manner 18-20 .

Carica papaya
Carica papaya belongs to family Caricaceae. Benzylisothiocynate and Papain are the main active constituents of Papya. Papain, papaya proteinase I, is a cysteine protease enzyme present in seed, fruit and leaves of papaya. The latex containing papain showed anthelmintic properties against intestinal nematodes of poultry 21 . Papain is comprised of a polypeptide chain with three disulfide bridges and a sulfhydryl group required for the enzyme activity which is responsible for digestion of nematodes cuticle 16 .

Streblus asper
Streblusasper family Moraceae exhibited a potent antifilarial activity. The main active components of Streblus asper are the cardiac glycosides strebloside and asperoside 2 .

Artemisia annua (Asteraceae)
Artemisia annua contains the sesquiterpene artemisinin which plays a vital role as an antimalarial agent. It showed a potent activity against P. falciparum. Various semi-synthetic derived products from artemisinin have been developed, and today in clinical practice 22 . Table  2 summarized the most important tantiparasitic medicinal plants and their secondary metabolites. While Table 3 showed the mode of action of different phytochemicals.

CONCLUSION
This review highlights the antiparasitic effects of different medicinal plants as well as the mode of action of different phytochemicals against parasites. So, the current review provides recommendations based on proof to understand the role of medicinal plants as antiparasitic agents aiming to be the first step towards the production of novel drugs for controlling the parasitic infection. Furthermore, more research is needed to run clinical trial to confirm the effect of medicinal plants as antiparasitic agents. In future, medicinal plants should be the first choice for the management of parasitic infection.

CONFLICTS OF INTEREST
No conflict of interest associated with this work.