The Reasonable Use of Antiparasite Druas for Animals

The Reasonable Use of Antiparasite Drugs for Animals

[Abstract] As the rapid development of scientific technology, especially the pharmaceutical industry, the kinds of antiparasite drugs increase rapidly. It’s of great importance to use antiparasite drugs reasonably. Currently, antiparasite drugs for animals can be classified into three main categories of vermifuge, antiprotozoal, insecticide and various other kinds. The ideal antiparasite drug should at least meet the requirements of safety, high efficiency, broad spectrum, low cumulation, and not easy to produce resistance. The main points of using antiparasite drugs for animals are: choosing drug properly, grasping the character of parasites, grasping the feature of host; paying attention to the quality, dosage and administration and compatibility of drugs; doing the relevant preparation work, administrating timely, paying attention to the drug combination; in addition, attentions should also be paid to rational use of drug, adjusting measures to local conditions; learning the adverse reactions of drug, avoiding producing drug resistant polypide.

I  Classification of antiparasite drugs for animals

Antiparasite drugs for animals are chemical substances used for prevention and treatment of animals’ parasitic diseases. It can be classified into vermifuge, antiprotozoal, and insecticide by the target subject.

1. Vermifuge   Vermifuge includes antinematode drug, antitapeworm drug,     antitrematode drug, and antischistosomal drug.

1.1 Antinematode drug can be divided into: Benzinidazole (Albendazole), Thiabendazole (Levamisole), Tetrahydropyrimidine (Pyrantel), Piperazines (Piperazidine), Organophosphorous (Trichlorfon), Antibiotics (Avermectin, Ivermectin, Doramectin, Destomycin A, Hygromycin B, ect.) and other categories (Thiophenylamine, Carbon Bisulfide, Tetracarp, Cyanoacetic Acid Hydrazide, etc.)

1.2 Antitapeworm drug can be divided into: Natural organic compounds (Arecoline), inorganic compound (Copper Sulphate) and synthetic organic compounds (Niclosamide).

1.3 Antitrematode drug can be divided into: Chlorhydrocarbons (Carbon Tetrachloride), Bisphenols (Lorothidol Bithin), Nitropheneol (Niclofelan), salicylanilide (Closantel), Sulfonamides (Clorsulon), Benzinidazole (Albendazole), and other categories (Bromofenofos).

1.4 Antischistosomal drug mainly includes Antimony Potassium Tartrate, Nithiocyamine, Praziquantel, etc.

1. Antiprotozoal    Antiprotozoal includes anticoccidial drug, antitrypanosomal, and anti-piroplasmosis drug.

2.1 Anticoccidial drug can be divided into:  Ionophore group (Monensin), Sulfonamides (Sulfaquinoxaline), Triazine (Diclazuril), Binitros (Nicarbazin), and other categories (including Amprolium, Clopidol, Robenidine, Halofuginone, etc.)

2.2  Antitrypanosomal mainly have Diminazene, Quinapyramine, Neoarsphenamine, etc.

2.3  Anti-piroplasmosis drug mainly have Diminazene, Quinuronium Metilsulfate, Artesunate, Acriflavine Hydrochloride, Trypan Blue, etc.

1. Insecticide   Insecticide is a kind of drug that can kill in vitro arthropod parasite (like acarus, tick, louse, flea, simuliidae, culicoides, mosquito, fly, fly maggot, wound maggot, etc.) which endangered the livestock and poultry.

Insecticide can be divided into: Organophosphorous (Diazinon, Safrotin, Malathion, etc.), Organochlorine (Lufenuron), Pyrethroids (Sumicidin, Deltamethrin) and other categories (Amitraz, Sublimed Sulfur, Cyromazine, etc.).

Ⅱ The conditions of ideal antiparasite drugs

1. Safety

Whatever antiparasite drug has some toxicity to the animals. So, a kind of ideal antiparasite drug requires a selective toxicity to the polypide and having toxicity to the host as little as possible.

The safety of anthelmintic is generally indicated by therapeutic index (therapeutic index= LD₅₀/ED₅₀) or safe range. The larger the index, the broader the distance, and less toxicity, and the drug is more safe to animal. It is generally acknowledged that a drug is suitable to clinical use only when the therapeutic index bigger than 3. For example, trichlorfon, piperazine, and mebendazole of antinematode drug, zoalene, amprolium, and robenidine of antiprotozoal, niclofelan and praziquantel of antitrematode drug, niclosamide of antitapeworm drug have a smaller toxicity, whereas, diminazene and copper sulfate have a greater toxicity.

1. High efficiency

The ideal high efficient antiparasite drugs should have an inhibitory or killing effect on the adult, larva, and eggs of parasites. The criteria to judge the effect of antiparasite drug is usually indicated by accurately calculating deworming rate and roughly calculating deworming rate. But from the requirements of practice, roughly calculated deworming rate is of greater clinical significance. High efficient antiparasite drug requires a roughly calculated deworming rate of more than 70% after the first administration. For example, among the current vermicide, praziquantel, levamisole, thiabendazole ect belongs to high efficient drug.

1. Broad spectrum

Animal parasitic diseases are mostly polyinfection, and are sometimes even polyinfection of different types of worms such as trematode, tapeworm, and nematode etc parasitizing at the same time. So, drug that is only effective to one or few kinds of parasites cannot meet the requirement of deworming. It requires the drug which can eliminate and kill various different kinds of polypide, thus can avoid using several drugs and the trouble of repeat administration. Such drugs as praziquantel, bithionol and mebendazole belong to broad spectrum drugs. Although some drugs have a narrow insecticidal spectrum, but they have special effect, such as oxantel which has special effect on trichinosis, and these drugs can be selected contrapuntally.

1. Low cumulation

Some antiparasite drugs have cumulatiuon effect in animal. For example, drugs like neoarsphenaminum and tiabendazole can remain for a long time in the body of animal, and this will bring harm not only to the animal itself, but also to humans who take its eggs, milk, and meat. The drug authority has established corresponding measurements to the use of such kind of drugs, which should be strictly complied with. For example, the animal’s milk is prohibited from drinking and internal organs are edible in at least 30 days after the administration of tiabendazole.

1. Not easy to produce drug resistance

The production of drug resistance causes a lot of disadvantages to the deworming work. Many antiparasite drugs are easy to produce drug resistance, such as naphthalene phenylsulfonylurea, zoalene and arprinocid. Clinically, such measures are taken to the drugs which have already produced drug resistance: Firstly, using other drugs. For example, coccidian has produced drug resistance to other anticoccidial drugs, and then nicarbazin can be used instead. Secondly, shuttle administration. It means using two or more kinds of anticoccidial drugs of different characters within one raising period. Thirdly, drug combination. For example, zoalene plus robenidine, sulfaquinoxaline plus amprolium, to treat coccidian; piperazidine plus carbon bisulfide, piperazidine plus dipterex, thiophenylamine plus piperazidine and levamisole, such drug combination can treat polyinfection of different kinds of nematode.

Ⅲ Main points of applying antiparasite drugs for animals

1. Choosing drug properly

When choosing antiparasite drugs, evidence must be based on different treating object, and the rule of high efficiency, low toxicity, broad spectrum, convenience, cheapness must be obeyed. Generally speaking, it’s best to use single antiparasite drug to repel various kind of parasites, and after few times and small amount of administration can thoroughly repel the in vivo and vitro parasites in the livestock and poultry with low toxicity, side effect and little drug residue, use convenient and cheap antiparasite drugs.

1. Grasping the character of parasite

Different types of parasite have different sensitivity to antiparasite drugs. For example, mezlocilline has an evident effect on intestinal nematodes and their larva in ruminant and it has a greater effect on longworms, it has good effect on Trichuris trichura, and has a relatively less good effect on tapeworm and trematode. Also, even the same polypide in different growing stages shows different sensitivity to drugs. For example, zoalene mainly inhibits propagation of gemma of the second parasexual cycle; amprolium mainly inhibits the growth and production of the coccidian first generation of agamont. Therefore, only when the characters of parasite are understood and the drugs are properly chosen can the effect of expelling worms be achieved.

1. Grasping the feature of host

Different species of animal show different sensitivity to drugs. For example, poultry and cattle are sensitive to dipterex, horse is sensitive to thiabendazole and lorothidol bithin, camel is even more sensitive to thiabendazole. Different individuals of the same species of livestock and poultry also have different sensitivity to antiparasite drugs. Besides, age and gender will also affect the therapeutic effectiveness. For example, benzoylimidazole is prohibited for sire breeder otherwise it will affect the quality of semen. Therefore, when choosing antiparasite drug, the features of animal should be fully considered.

1. Pay attention to the quality, dosage and administration and compatibility of drug

The quality of drug can not only affect the deworming effect, but also concern the safety of animal. For example, only refined products instead of crude products of dipterex can be used, otherwise it will increase the drug’s toxicity. Moreover, drugs which are expired or deteriorated owing to misconduct cannot be used. Antiparasite drugs should be used according to the prescribed dose; overdose will usually cause poisoning of animal; insufficient dose will not only fail to achieve the deworming effect, but also cause the polypide to produce drug resistance.

Antiparasite drug can be administrated by intramuscular, oral administration and external use. When administrating by mixing the drug with feeds, attention should be paid to uniform mixture; when administrating by drinking water, the drug should be fully dissolved, and to improve the deworming efficacy and shorting the medication time, a fast could be carried out. When administrating by external spraying, one should constantly driving the animal to make the periphery fully contacted with drug.

Some drugs have strong irritation; take carbon tetrachloride and praziquantel as example, when administrated by intramuscular injection, they should be mixed with equivalent dose of liquid paraffin to alleviate pain; naphthalene phenylsulfonylurea combined with calcium chloride can excite the function of reticuloendothelial system thus improving its deworming effect; diminazene combined V_B1, cobalt chloride, copper sulphate can improve its effect of deworming trypanosome. However some drugs are strictly prohibited to combine with other drugs. For example, amprolium cannot be used together with V_B1, otherwise it will reduce the deworming effect; mezlocilline cannot be used together with bromosalicylanilide, or it will cause miscarriage of cattle and death of sheep. Besides the combination of several antiparasite drugs because of polyinfection of livestock and poultry, auxiliary medication is also of great importance. For instance, when deworming gastrointestinal nematode in livestock and poultry, in order to fully exert the effect of drug to polypide, we can administrate before feeding in the early morning, or stop feeding 6-12 hour before administration, at the same time, use saline cathartic when or after giving the antiparasite drug to discharge the paralytic polypide or residual drug in gastrointestinal tract.

1. Do the relevant preparation work

According to different species of livestock and poultry, and different deworming objects, do the work of preparing drugs, administration apparatus (injector and sprayer etc.) and cleaning the breeding house. Before carrying out deworming to a large number of livestock and poultry, or using several drugs to treat polyinfection, pre-experiment should be done and carefully observing the reaction and effect. The project can be carried out to a large scale after proved safe and effective. Moreover, no matter batch administration, or pre-experiment, the character of antiparasite drugs should be known and the corresponding antidotes should be prepared. Nursing and observation to livestock and poultry should be strengthened around the application of antiparasite drug. Animals found weak and sick should immediately be isolated or stop deworming temporarily; animals found abnormal or toxic should be rescued in time; innocent treatment of animal faeces should be strengthened to avoid pathogens spreading; do the cleaning and sterilization work of the breeding house. Clean and sterilize the facilities like apparatus, feeding trough and watering trough periodically.

1. Administrate timely

Young cattle and sheep generally do the first deworming between August to October every year. Pregnant dams (cattle and sheep) do the prenatal deworming near delivery. Pig farms should deworm once in spring and autumn respectively. Pregnant sow should deworm once 2 weeks before delivery. Piglet should deworm once at day 30 and day 60 respectively. It is better to be administrated at night fall for poultry, and after the first deworming, a second should be carried out at an interval time.

1. Use rationally and adjust measures to local conditions

Rational use of antiparasite drugs is an important link. In the progress of application, in order to achieve the best therapeutic effect, we should grasp the epidemic data in the region, damage degree and parasitic method of the verminosis; learn the functional status and drug reactions of the host; get familiar with the physical and chemical properties of drug; adopt the reasonable dosage form, dose, course of treatment and method.

1. Learn the adverse reactions of drug

Usually, antiparasite drugs are relatively safe to the host, but irrational drug use (overdose, long course of treatment, misusage) will cause certain adverse reaction and even death to the organism. Therefore, when using drug, apart from accurate calculation of dose, course of treatment and method of administration should also be noticed. To avoid toxication phenomena of a large quantity, pilot test should be done to the minority animals of the whole drove before using antiparasite drug to deworm at large scale.

1. Avoid producing drug resistant polypide

Repeated small dose or longterm use of a same antiparasite drug may lead the polypide to produce drug resistance or even appear cross resistance to drugs of a same kind, thus reducing the efficacy of deworming. In practice, frequent change or alternative use different types of antiparasite drugs can avoid or reduce the drug resistance.

1. Assure the safety of human health

The distribution in animal body and residual quantity and duration in tissue of some antiparasite drugs are of great importance to human health. Some antiparasite drugs will remain in livestock products (meat, milk, eggs, etc.) for human use which will do harm to human health and cause severe public hazard. For this reason, many countries have established a permitted residue limit (if exceed, cannot be sold on the market) to avoid bad effect to the human body thus assuring the safety of human.

References

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[5] Zhu Mozhong. Veterinary Antiparasite Drug [M]. Bejing: Chinese Agriculture Press, 1983.

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