THERE ARE multiple factors which play their role in establishing the economy of any country. Among these factors, Livestock has vital role in the economic strength of any country by producing, milk, meat, wool, hide, farm yard manure and many other animal by-products. There are 1750.5 million heads of cattle and buffaloes, 2439.2 million heads of sheep and goats, 27.4 million heads of camel and 21554.8 million heads of chickens are found worldwide which are producing milk 770.8 million tonnes (cattle and buffaloes) and 4.5 million tonne from sheep while camel are also producing about 1.7 million tones of milk worldwide while meat production of these species reported worldwide is about 65,838 thousand tonnes by cattle and buffaloes and 150,48 thousand tones by sheep and goat.
In Pakistan, Livestock sector being the most important component of agricultural economy shares about more than 50% in agricultural GDP. Large ruminants being the part of domestic livestock share big part in compensating the meat requirement by producing 47,951 thousand tons milk and 1,887 thousand tons meat while sheep and goats producing 860 thousand tons of milk and 657 thousand tons of meat while camel shares about 851 thousand tonnes of milk and it also used as draught animal in desert area worldwide. Apart from a production point of view, livestock sector also provides means of earning by giving the source of employment and earning money by the sale of animals, their hides, wool and by-products like butter, yoghurt etc.
Factors affecting the livestock production
There are some factors which are affecting livestock population by decreasing their production and ultimate economic value of the animals. These factors include environmental conditions (temperature and humidity), socio-economic conditions, nutritional deficiency of animals, poor husbandry management, poor hygienic measures at the farm, use of contaminated instruments and utensils etc. All these factors predispose the animals to different diseases caused by bacteria, viruses and parasites leading the animal towards emaciation, loss, in general, body condition, production loss and sometimes leads to the death of the animal by exposing the animal to other life-threatening conditions. Amongst these disease-causing agents (bacteria, viruses and parasites), the prevalence of diseases caused by parasites is increasing day by day.
Role of gastrointestinal parasitism
Parasitism is of extreme importance in livestock industry causing widespread economic losses worldwide, in terms of decrease in milk yield, meat production, growth rate, reproduction and loss due to mortality. The parasitism caused by parasites can be divided into 2 categories as endoparasitism caused by endoparasites like helminths (nematodes, trematodes and cestodes) and ectoparasitism caused by ectoparasites (ticks, mosquitoes, mites, lice, fleas and flies). Endoparasitism caused by helminths is increasing day by day.
The prevalence of gastrointestinal parasitism caused by these helminths is continuously increasing and the reason of increasing gastrointestinal parasitism is their antigenic variation. With the help of antigenic variation, parasites can evade host immune response. In antigenic variation mechanism when a parasite e.g. Haemonchus contortions enters into the body of the host, it change its surface proteins which are not recognized by the host immune system. In this way, antigenic variation not only aid parasite to evade host immune response but also allow the parasite to cause the re-infection of the susceptible host as antigen produced by the pathogen will not be recognized by the host immune response and infection occurs again and again. Due to this ability of antigenic variation gastrointestinal parasitism cause economic losses at individual as well as at farm or herd level.
Estimated economic losses in terms of production vary from 15-55% depending upon the hygienic measures were taken and use of dewormers to control gastrointestinal parasitism. However, veterinary doctors and livestock producers are also trying to combat the endoparasitism by using chemical anthelmintics.
Failure of anthelmintics against GI Parasitism
The use of chemical anthelmintics is as old as the 1950s when 1st generation broad spectrum anthelmintics including phenothiazine and piperazine were produced after that with the passage of time more advanced and effective anthelmintics evolved as in 1960s containing 2nd generation anthelmintics like imidazothiazoles, benzimidazoles, pro benzimidazoles and tetra-hydro-pyrimidines were produced while in the 1980s a 3rd generation broad spectrum anthelmintics including macrocyclic lactones (Avermectins) have been produced which are still functional and being used by the veterinarians and livestock producers either in the form of injectable or drenching the animals like sheep, goat and cattle etc.
In spite of using broad spectrum as well as narrow spectrum anthelmintics, the endoparasitism is continuously emerging as a serious threat to the livestock population. There are many factors which might be responsible for this failure like the use of outdated dewormers, improper dose rate and time of deworming, age, sex and breed of animals.
An important factor while considering the failure of anthelmintics is their extensive use about 8-12 times/year which results in development of resistant parasites against various anthelmintics along with this helminths have different stages of their life cycle like egg, larva, nymph and adult and each stage of their life cycle have different antigen which is difficult to recognize by the host immune response which cause failure of anthelmintic therapy.
History of development of anthelmintic resistance
The first report on parasitic resistance was reported in 1957 against phenothiazine and it was also observed that resistance developed after few years of development of drug and mostly reported parasite was Haemoncus contortus (nematode). Some parasites which are reported to develop resistance against anthelmentics include Haemoncus contortus against various groups of drugs including phenothiazine, thiabendazole, levamizole, rafoxamide, ivermectin, macrocyclic lactones and organophosphates. Ostertagia, Trichostrongylus and Cooperia species against Benzimidazoles, imidazothiazoles and macrocyclic lactones while Fasciola hepatica against benzimidazoles.
Mechanism of development of anthelmintic resistance
The mechanism of development of resistance against anthelmentics is not happening suddenly, but there are certain phases after which parasites become resistant. In 1st phase there are less number of parasites which develop resistance against specific anthelmentics then there is an intermediate phase in which heterozygous parasites (which survived in 1st exposure) population develop resistance and in the final phase when same individuals are expose to same anthelmentics they all develop resistance against that anthelmentics drug this population become homozygous population of parasites. It is also observed that when species of parasites became resistant against one class of anthelmintics they also become resistant against some other group of anthelmintics.
To cope with these resistant parasites and to control the gastrointestinal parasitism veterinarians and livestock producers are using some natural anthelmintics which are proven effective to control the problem.
Medicinal plants used against gastrointestinal parasitism
The natural anthelmintics includes Neem, Tobacco, Walnut, Tulsi, Garlic and Kalonji seeds of different plants and honey and vinegar mixed with hot water act as vermifugal substances as anthelmintics. Seeds of garlic, onion and mint has been used against gastrointestinal parasitism, extract of Tobacco plant has been proved effective against various ectoparasites, some natural anthelmintic plants and their different parts like seeds, leaves, bark as such or their ether extracts which are proved to be effective against different helminths include Azadirachta indica (Neem) against Strongyloid, Plasmodium and Trypanosomes, seed extract of Trachyspermum Ammi Linn. (Ajowan) against Haemoncus contortus, leaves extract of Cannabis sativa Linn. Against Flukes and Trifolium repin Linn against Hymenolepis dimminuta. Allium sativum against Haemoncus contortus, Crataeva nurvala and Artemesia pallens and Butea monosperma against earthworm, tapeworm and roundworms proved effective. Ether and aqueous extract of leaves of the Adhatoda vasica proved effective against larvicidal and ovicidal activity of Nematodes.
The stem bark extract of Acacia oxyphylla against Ascaridia galli (Nematode), seeds of Carum capticum against gastrointestinal nematodes of sheep, aqueous and ethanolic leaf extract of Adhatoda vasica has been observed for ovicidal as well as larvicidal activity against nematodes, leaves of Artimesia bervifolia (wormwood) and Zanthxylum zanthoxyloides (Fagara a native tree from Africa) in the form of powder has been proved effective up to 65% against eggs of Haemonchus contortus in abomasum, hay of Cassava forage has been proved effective against eggs and larva of abomasal and intestinal nematodes of sheep and goats, Punica granatum commonly known as (Anar) the roots and bark of the stem of this plant has been used as astringent (antidiarrheal) and anthelmintic plant and experimentally proved that the alcoholic extract of the stem bark of this plant inhibit the hatching of Haemonchus contortus eggs to filiform larvae, the aqueous, alcoholic and ether extract from seeds of the plant Cucurbita maxima has proved its vermifugal activity experimentally against Platyhelminthes (trematode and cestodes) and NEMA helminths (nematodes) both In Vitro as well as In Vivo trials. The alcoholic and ether extract of Mucuna prurita has been found active against the trematodes.
There are numerous species of plants reported worldwide, which are effective against different species of helminthes.
Future prospects and present scenario about medicinal plants
It is estimated that there are more than 35 species of plants which are being used worldwide against Cestodes, 20 against trematodes and more than 40 against nematodes. However, there are thousands of plant species which are being used by the small farmers and producers and have not been proved yet. Therefore, there is a need to identify and evaluate the species of plants as whole, as well as their parts (bark, leaves, stem, flowers and fruits). There is need to study that which part of the plant is effective either against specific species of parasite or multiple species of parasites and how much concentration is sufficient to get response of therapy.
For this purpose, there are some tests which are available for diagnosis of resistance of parasites against anthelmintics and also to evaluate the efficacy of medicinal plants anthelmentic activity In vivo as well as in vitro. These test includes, eggs per gram (EPG), packed cell volume (PCV) showing degree of anaemia, worm recovery method, through proximate analysis of medicinal plants, egg hatch assay or larval development assay, adult development assay and DNA probes, Copro-ELISA (Enzyme-linked immune sorbent assay) and PCR (polymerase chain reaction) are also available for research purposes but not commercially available. Although anthelmintic plants have good activity against various helminths as well as other parasites but there is a need to study in detail about phytochemical properties of plants, their chemical profile at molecular level and their other properties and harmful effects of their excessive use so that in future we will be able to control increasing parasitism and ultimately minimize economic losses in terms of productivity.
The research is being conducted on the effect of medicinal plants on gastrointestinal parasitism of sheep and their mineral profile in molecular parasitology laboratory, University of Agriculture, Faisalabad. The result of this research will be helpful in identification of medicinal plants with their mineral composition and effect on gastrointestinal parasitism and provide guidelines for their safe use in livestock industry to control parasitism and ultimate economic losses.