Parasitic disease is one of the most common and important diseases in the breeding industry. It has the characteristics of a wide distribution, high infection rate and great harm. Usually, the control of parasitic diseases is to use chemical drugs to deworm. In recent years, studies have found that several deworming medicines (such as ivermectin, avermectin, albendazole, etc.) have different drug resistance in some areas, and farmers who used these medicines report that the effect is not as good as before. So this article provides some reference for correct choice and use of deworming medicines for some livestock.
Overview of Ivermectin Resistance Research
Parasite drug resistance generally refers to the decrease or even disappearance of drug sensitivity after the parasite has been in contact with drugs for many times, resulting in reduced or ineffective antiparasitic efficacy of the drug.
Ivermectin, as a broad-spectrum, high-efficiency, and low-toxicity deworming agent, has been widely used to repel a variety of animal parasites inside and outside of animal body. It has played an irreplaceable role in veterinary clinics. However, with its extensive and long-term use, some reports regarding different degrees of drug resistance has been published. Some reports as below:
1985 South Africa: A strain of Haemonchus contortus that is resistant to ivermectin was screened out；
1989 Denmark: Sheep nematodes in 15 regions are resistant to ivermectin and albendazole
1996 Uruguay: Among 45 sheep farms detected, 26.7% developed resistance to ivermectin, 17.6% developed resistance fo albendazole, 35.3% developed resistant to both medicines. （26.7%+17.6%+35.3%=79.6%）
2004 Argentina: Haemonchus contortus developed resistance to both ivermectin and albendazole.
2004 Australia:After 5 years consecutive use of ivermectin, 235 farms developed resistance.
Mechanism of Worm Resistance to Ivermectin
Ivermectin acts on the alpha subunit of the glutamate-gated chloride channel on the cell membrane, which leads to an increase in the permeability of the cell membrane to chloridion. Excessive chloridion enter the central cells and affect the transmission of central neurotransmitters, resulting in parasites’ paralysis and death. After drug resistance occurs, the binding properties of glutamate-gated chloride channels change, making the worms insensitive to these drugs. Different types of parasites have different resistance mechanisms to ivermectin.
Cause of Resistance：
1. The long-term repeated use of a single deworming drug causes drug resistance due to a same target and selective pressure
2. Ignore of the physiological differences between different hosts is also the cause of resistance. Abamectin drugs are more effective in goats than in sheep, and the effective dose for goats may not be effective for sheep;
3. Estimating animal weight based on experience, and inaccurate estimation leads to long-term sub-dose or over-dose administration, This can also cause drug resistance.
4. If a newly introduced herd was not dewormed or dewormed incompletely, it may introduce some drug-resistant strains and spread in the new herd.
5. Failed to formulate a scientific and reasonable deworming process based on the actual conditions of farms. Or after the herd is dewormed, there was no disinfection of the feces and places.
In summary, the resistance of parasites is widespread and persistent. So a correct choice of deworming drugs is the key to solving the resistance.
Correct Choice an Use of Dewormer.
Closantel Sodium: It is a new type of broad-spectrum antiparasitic drug, which can inhibit the phosphorylation process of mitochondria of the worm, thereby preventing the synthesis of adenosine triphosphate (ATP) in the worm’s body, weakening the energy metabolism of the worm rapidly and finally die. It has a strong repellent effect on cattle, sheep fasciola, gastrointestinal nematodes and arthropod larvae. Related research shows that no sheep fecal worm eggs turned negative at the time point set by the experimental group within 30 days of the administration of ivermectin and albendazole. While the Closantel Sodium group began to turn negative after 60 hours and only a few worm eggs were detected after 30 days.
Doramectin: Doramectin has the characteristics of high efficiency, safety, low toxicity, small dosage, no drug-resistance, and no cross-resistance with other antiparasitic drugs. It is highly effective for gastrointestinal nematodes, lung nematodes, lice, ticks, mites, and wound maggots. The blood concentration and half-life period are both higher or twice as prolonged than ivermectin.
A search in 2016 on deworming effect of doramectin and ivermectin on grazing cattle and sheep in alpine regions showed that the deworming effect of doramectin was better than that of ivermectin.
Eprinomectin (cattle): It is effective for larvae and adults of nematodes and arthropod adults. Subcutaneous injection can repel 95% of larvae and adults, and it can repel larvae of bovine fly up to 100%.
Combination Preparation: By combining different drugs into new preparations, antiparasitic drugs with a broader anti-insect spectrum can be obtained, such as ivermectin + albendazole, ivermectin + Closantel , ivermectin + clorsulon, ivermectin + praziquantel, oxyclozanide + levamisole, etc. Some as below:
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Post time: Aug-15-2020