Why is anthelmintic resistance a problem?
Good worm control is highly dependent on effective worming products. However, a direct and unavoidable consequence of continuous use of wormers is the development of drug resistant worms, known as anthelmintic resistance. Resistant worms are those that can survive a dose of the wormer that would normally kill them.
A worm is said to be resistant if it survives exposure to the standard recommended dose of the anthelmintic. Anthelmintic resistance is said to exist in a population of worms if more than 5% of the worms survive treatment.
In the absence of effective vaccines and adequate sanitation, prophylaxis and treatment commonly rely upon anthelmintics. There are concerns about the development of drug resistance, side-effects, lack of efficacy and cost-effectiveness that drive the need for new classes of anthelmintics.
Applying a better grazing management is a possible and helpful method to reduce the frequency anthelmintic use. Lowering of the stocking rate and the grazing period on the pastures, and applying mixed grazing among different animal species are key factors for a better grazing practice.
Definition of Anthelmintic Resistance
AR is a heritable loss of sensitivity of an anthelmintic in a parasite population that was in the past susceptible to the same anthelmintic.
Antimicrobial resistance happens when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. Resistant infections can be difficult, and sometimes impossible, to treat.
The major method for the detection of resistance remains the faecal egg count reduction test (FECRT) that can be used with all anthelmintic groups. Nematode eggs are counted in faeces at the time of treatment and at defined times after treatment, the time depending on the anthelmintic group used.
Resistance to the benzimidazole (BZ) anthelmintics is inherited as an incomplete dominant/ incomplete recessive trait and is now widespread in populations of gastrointestinal nematode parasites of sheep.
The in vivo faecal egg count reduction test (FECRT) is the most commonly used test to detect anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) of ruminants in pasture based systems. However, there are several variations on the method, some more appropriate than others in specific circumstances.
The pros are the slowing of resistance prevalence, lower residues of anthelmintics in meat and milk, and lower cost; the cons are the difficulty and time spent on selecting animals in need of treatment and the possibility of lower production.
What is the purpose of an anthelmintic?
Anthelmintic is the term used to describe a drug used to treat infections of animals with parasitic worms.
Most anthelmintics have wide safety margins, ie, the dosage that can be given to an animal before adverse effects are induced is much higher than the dosage recommended for use. The wide safety margin of benzimidazoles is because of their greater selective affinity for parasitic β-tubulin than for mammalian tissues.
Anthelmintic resistance is detected by a FEC reduction test (FECRT), with resistance declared if the reduction in egg count is <95% and the lower confidence limit is <90%.
The factors that can explain the emergence of resistance are: Reduction of drug concentration within the parasite, either by decreasing drug uptake or by increasing efflux of the drug; inhibition of drug activation; inactivation of active drug; and gene amplification .
Causes of resistance
At its most basic level, anthelmintic resistance occurs due to the high genetic diversity that exists within populations of gastrointestinal roundworms. Some individual parasites may carry mutations that they inherited from their parents which help them survive exposure to dewormers.
HOW DO ANTHELMINTICS WORK? Anthelmintics are drugs used for treating parasitic infections. They kill parasites by: Binding to nerves and muscle cells and causing paralysis and eventually death of the parasite.
Failure to respond to antibiotics includes the emergence of resistant organisms, superinfections, and drug interactions. The most common mistake made with apparent antibiotic failure is to change or add additional antibiotics.
- Wrong antibiotic choice.
- Delayed administration of antibiotics.
- Inadequate source control.
- Inadequate antimicrobial blood levels.
- Inadequate penetration of the antimicrobial to the target site,
- Antimicrobial neutralization or antagonism,
Penicillin was successful in controlling bacterial infections among World War II soldiers. However, shortly thereafter, penicillin resistance became a substantial clinical problem, so that, by the 1950s, many of the advances of the prior decade were threatened.
In over 1/3 of the operations tested, anthelmintic treatment resulted in < 90% reduction in FEC approximately 2 wk after treatment. The FECRT data are key components of licensing new anthelmintics where the average FECRT value for all trials submitted must be ≥ 90%.
How do you test for parasite resistance?
To determine the presence of resistant parasites, the most effective method is the Fecal Egg Count Reduction Test (FECRT). Collect a fecal sample prior to treating animal with an anthelmintic, and another sample approximately two weeks later.
Conclusion. Routine administration of intestinal anthelmintic drugs results in a marginal increase in haemoglobin (1.71 g/l), which could translate on a public health scale into a small (5% to 10%) reduction in the prevalence of anaemia in populations with a relatively high prevalence of intestinal helminthiasis.
Commonly used ones are mebendazole and its analogues flubendazole, piperazine, praziquantel and pyrantel. Others such as levamisole and pyrvinium have previously been used but not common any more. Mebendazole, flubendazole, piperazine and pyrantel are indicated for roundworm infections.
|Drug Name||Avg. Rating||Reviews|
|Albenza (Pro) Generic name: albendazole||8.0||3 reviews|
|Emverm (Pro) Generic name: mebendazole||1.0||2 reviews|
|Biltricide (Pro) Generic name: praziquantel||5.3||2 reviews|
|Vermox (Pro) Generic name: mebendazole||8.5||1 review|
Anthelmintic drugs is the collective term for the group of drugs which treat infections of animals or humans infected with parasitic worms (helminths).
Anthelmintics are drugs that are used to treat infections caused by parasitic worms (helminths) .
Drug resistance usually leads to a delay or failure to clear asexual parasites from the peripheral blood that eventually enable production of gametocytes which are responsible for transmission of the resistant genotype.
Some antiparasitic medications can cause serious health problems if you take more than you should or you take them for too long. These problems include: Kidney failure. Vision problems, including blindness.
As it replicates, the virus's genetic makeup may mutate (change). If a virus goes through too many changes, the antiviral drug won't recognize the new virus variant (version of the virus). Once a virus is drug resistant, the medication can't keep it from multiplying.
Why do viruses become drug resistant?
Prolonged antiviral drug exposure and ongoing viral replication due to immunosuppression are key factors in the development of antiviral drug resistance, which may manifest as persistent or increasing viremia or disease despite therapy.
Why is it more difficult to develop a vaccine for parasites than for many viruses? Parasites go through a series of life stages and occupy several different niches in the body. They've also developed clever mechanisms to evade the immune system. So parasitic infections are the ultimate challenge.
Anthelmintic is the term used to describe a drug used to treat infections of animals with parasitic worms. This includes both flat worms, e.g., flukes (trematodes) and tapeworms (cestodes) as well as round worms (nematodes).
Anthelmintics have been an effective way of controlling worms and fluke for many years.
All are chemical agents and are generally administered orally, and many are used in both human and veterinary medicine. No anthelmintic, however, is completely effective, completely without toxic effect upon the host, or equally active against all worms.
Antimicrobial Resistance (AMR) occurs when bacteria, viruses, fungi and parasites change over time and no longer respond to medicines making infections harder to treat and increasing the risk of disease spread, severe illness and death.
Antibiotic resistance results in a decreased ability to treat infections and illnesses in people, animals and plants. This can lead to the following problems: increased human illness, suffering and death, increased cost and length of treatments, and.
The parasitic resistance may happen by intrinsic or acquired type. Intrinsic or natural resistance is due to the parasite own characteristics which makes it insensitive to the effect of the drug.
Two tests are recommended, an in vivo test, the faecal egg count reduction test for use in infected animals, and an in vitro test, the egg hatch test for detection of benzimidazole resistance in nematodes that hatch shortly after embryonation.
Treatment of moderate-to-severe anaemia improves appetite, growth and cognitive and school performance in children, and also improves work and social capacity and productivity in children and adults.