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Revisiting Pet Deworming
By: Michael Ephraim Vergara, DVM, Technical Services Associate
Pet deworming can be one of the routine procedures some owners tend to forget. There will be times also, it is neglected. But in the advent of new technologies and yes, even global warming – information on deworming and even the ecology of these helminthes are either changing or influenced. So with that, here’s the excerpt of the article from an
expert on pet deworming has to say:
Pet roundworms and hookworms:
A continuing need for global worming
Donato Traversa – Faculty of Veterinary Medicine
Department of Comparative Biomedical Sciences,
University of Teramo, Teramo, Italy
The relationship between human beings and domesticated small animals began about 15.000 years ago. Such association has led to the dispersion of pets all over the World, along with the spread of their pathogens. Some of them are common and zoonotic: as a consequence, there is a continuing interest in their sanitary impact, and on prevention and control methods. In the past few years, the attention of the Scientific Community has been attracted by feline and canine extra-intestinal parasitic nematodes, which are emerging in several countries and spreading into regions previously free from these parasites. Indeed, global climate change is influencing the ecology of helminths with multiple hosts and different transmission routes.
Different species of ascarids (commonly known as “roundworms”) and ancylostomatids (commonly known as “hookworms”) may affect the small intestine of dogs and cats. Actually, they remain the most important parasites affecting companion animals worldwide and maintain the primacy in terms of dispersion and risk for animal and human health.
There is, in turn, a significant merit in keeping our guard up against these nematodes even when other parasites are attracting attention and interest. Therefore, the aim of this article is to review the most important features of roundworms and hookworms affecting companion animals, along with critical and focused appraisals on the importance of their pathogenicity, epidemiology and control methods in veterinary and human medicine.
Intestinal nematodes are complex and interesting
T oxocara canis and Toxocara cati are the two major ascarids globally infecting dogs and cats, respectively. Both species have a complex and fascinating biological cycle, which relies on different pathways of larval migrations and transmission, depending upon mainly the source of infection and animal age. Bitches are a major source of infection for their offspring because, after an infection occurs in their life, they harbour somatic larvae. These resting larvae will mobilize during pregnancies and infect subsequent litters even when re-infections do not occur. Pups become infected in utero by the second month of gestation, which results in egg shedding after a minimum period of about two weeks after birth. When mobilized larvae are transmitted via the lactogenic route litters can also be infected by colostrum and milk for at least 38 days after delivery. These vertical infections occur regardless of the presence of the intestinal parasitosis in the bitch but, in general, a proportion of mobilized larvae may reach the intestine of the dam, then mature and cause a patent infection with high egg shedding lasting weeks after whelping. Bitches can be reinfected also by ingesting immature ascarids defecated by their suckling offspring. Therefore, lactation may either cause or reinforce a patent infection in bitches, which provides another source of environmental contamination and infection for puppies.
Among the most common hookworms, Ancylostoma caninum and Ancylostoma tubaeforme are species-specific for dogs and cats respectively, while Ancylostoma braziliense, Ancylostoma ceylanicum and Uncinaria stenocephala affect both species. In general A. caninum, A. tubaeforme and U. stenocephala are spread especially in warm countries (Ancylostoma spp.) and in colder areas of temperate and subarctic regions (U. stenocephala) in both hemispheres; the remaining hookworms are most often present in sub-tropical and tropical countries. As for roundworms, hookworms have a complex biological cycle, in which different sources and ways of infection are possible. The most important infectious stage is represented by filariform larvae present in the soil, which infect a suitable host by actively penetrating the skin (especially for Ancylostoma spp.) and/or via the oral route (i.e. Ancylostoma spp., Uncinaria spp.).
In summary, there are major factors making roundworms and hookworms the most common endoparasites in pets all over the World. First of all, the possibility of puppies and kittens being infected by their dam by transmammary and/or transplacental route/s is a powerful host-finding strategy. Also, pups have daily thousands egg counts forT. canis and animals often shed millions of hookworm eggs for weeks, thus causing a high environmental contamination. Ascarid eggs can survive for years in extreme environmental conditions, thus are available for ingestion at any time. Infected paratenic hosts are ubiquitous, being a constant source of infection especially for cats, given their hunting instinct.
Is age a decisive circumstance for host-finding strategies of intestinal nematodes?
There is a long-standing misconception on the age categories of dogs and cats, which can be infected. In fact, it is often thought that “intestinal worms” are only a health problem of puppies and kittens and that adult animals are, instead, resistant. The real truth is that pets are exposed to roundworm and hookworm infections throughout the year and for all their life. Specifically, parasitic burdens, egg output, and infection rates are higher in puppies and kittens but it is nowadays established that patent intestinal infections occur in dogs and cats of all ages.
An investigation carried out in the USA on the most common canine and feline endoparasites in thousands of pets have shown that after animals under 6 months of age (as expected), the most parasitized category of animals are patients more than 10 years old. The possible explanation of such a high degree of parasitism in old animals may reside in a loss of immune response against previously experienced parasites. Another possible reason may be a loss of compliance of pet owners, who, perhaps, become less willing to engage in chemo-preventative measures in old pets. Such changing approach of pet owners should be discouraged by veterinarians not only for the pathogenicity of intestinal worms but also because there is no practical reason to consider an old animal a less effective source of infection for other pets and human beings in comparison to puppies and kittens.
Pet roundworms and hookworms are zoonotic
Soil-transmitted helminthoses affects more than 2 billion people worldwide. The zoonotic ability of Toxocara spp. has been established since the 1950’s and presently it is well known that pet ascarids cause human infections globally, as demonstrated by several surveys carried out in all corners of the World. Indeed, T. canis is largely acknowledged as a major culprit of human syndromes by animal ascarids, but it is likely that some human infections are caused by T. cati as well. Some infections are asymptomatic and the degree of damage and elicited signs depend upon the tissue/s invaded, number of migrating larvae, host, age and immune response. When symptoms are present, two major syndromes may occur, i.e. the so-called “visceral larva migrans” (VLM), encompassing important organs (mainly liver, lungs, brain) and “ocular larva migrans” (OLM), due to damage to eye and optic nerve; other minor syndromes, e.g. covert, neural, and atopic toxocarosis, are also reported.
Treatment and control methods: Need for compromises?
Different parasiticide classes are available for treatment and control of intestinal nematodes, being (pro-) benzimidazoles (e.g. febantel, fenbendazole), tetrahydropirimidines (e.g. pyrantel), cyclooctadepsipeptides (i.e. emodepside) and macrocyclic lactones (e.g. ivermectin, selamectin, moxidectin, milbemycin oxime) the most used.
Provided below are some key examples of major molecules available for treatment and control of ascarids and ancylostomatids.
A multi-centric investigation indicated that the combination of febantel, pyrantel and praziquantel has an efficacy of ~99.9% against canine T. canis and hookworms.
Regular “de-worming” or “worming”, an imprecise term but common in daily language today, is the basis for an effective chemoprophylaxis irrespective of the age of the pet.
The US Companion Animal Parasite Council (CAPC) and the European Scientific Counsel Companion Animal Parasites (ESCCAP) have published guidelines for treatment and control of major parasites affecting companion animals.
Treatment of puppies and kittens at two, four, six and eight weeks of age is suggested by CAPC. Thereafter, animals should be put on monthly preventives as soon as label recommendations allow.
The ESCCAP recently advised that pups should receive a parasiticide at 2 weeks of age, then at fortnightly intervals until two weeks after weaning. Thereafter, puppies should undergo monthly treatments until six months old. Fortnightly treatment of kittens can start at 3 weeks of age and should be repeated fortnightly until two weeks after weaning, then monthly for six months.
A compromise between these two views from North America and Europe seems to be a good choice if particular situations do not apply. A minimum number of 4 administrations per year or treatments at intervals of 4–6 weeks can be effective in preventing most patent infections, while a worming frequency of less than 3–4 times per year does not influence parasite prevalence.
As mentioned earlier, in US settings the routine monthly parasiticide administration is sometimes performed along with annual or semi-annual fecal examinations.
Veterinarians should convince pet owners of the importance of periodic fecal examinations. In the first year of life any pet should undergo at least 2–4 copromicroscopic examinations and then, when adult, it should be examined more than once per year according to health status, lifestyle and frequency of treatments.
Given the clinical importance of intestinal nematodes affecting pets, their ubiquitous presence and the zoonotic impact some of them have, public education is crucial for reducing risk exposure in both humans and companion animals. At the same time pet owners and, in general, the public opinion should maintain a self-confidence that keeping a pet is safe and a positive experience. This is also true when close-contact occurs between the pet and the owner, even when some behavior can be questionable. Owners should have confidence that ownership of any companion animal is beneficial and safe as long as their pets are healthy.
Companion animals represent a way of life for a lot of the people and this relationship provides socialization, mental health, and physical well-being: those who own a pet have been shown to display reduction in blood pressure and cholesterol levels, require less medical care, and it has also been reported that there is an improvement of life quality and quick recovery after heartbreaking events. Therefore, owning companion animals is vital for the majority of families, especially when children and the elderly are present. However, the potential risks of pet originating zoonoses should always be kept in mind. This has become even more so in recent years when several sociological changes have influenced the relationships between physicians and veterinarians. In fact, the major goal of the re-discovered “One Health Program” (i.e. “the collaborative work of multiple disciplines to help attain optimal health of people, animals, and our environment”) highlights the crucial role of a tight tie between the human health operators, vet practitioners, and the general public.
A desirable goal for effective control programs would also be to understand which are changes and trends in terms of prevalence of infection by ascarids and hookworms in canine and feline populations, with the simultaneous aim to track the incidence of human cases caused by each of the single aetiological agents. This would be a basic step to cope with current weaknesses in prevention approaches and to establish where to intervene with focused plans. In fact, updated information on the prevalence of parasites of dogs and cats and the risk factors associated with infection, as well as reinforcing veterinary and public health concerns, is of crucial relevance because common awareness is non-existent or often based on outdated information.
Given that parasitic zoonoses are too often neglected or underappreciated, and may be mismanaged or underdiagnosed by veterinarians and physicians, a strong education outreach by veterinary and medical practitioners should be accomplished. Veterinarians must keep their guard up against zoonotic parasitoses of pets and constantly provide advice and improve knowledge of their clients, with a special focus on those human categories, who are at higher risk of infection, in order to allow pets to remain integral members of household and families. Furthermore, owners should become aware of “invisible” beneficial effects of a lifespan control program based on routine fecal examinations and frequent worming.
New concepts for accurate preventative plans have been generated based on several individual and epidemiological circumstances. The role of the veterinarians and constant compliance of the owners are crucial to the success of worm control programs in pets. Additionally, the present climate changes and global warming supports the need for a continuous global worming, given that faster egg embryonation and increased over-wintering of infectious elements in the environment will likely increase the spread of helminths affecting companion animals and humans in several areas of the World, as recently hypothesized for sub-Arctic and Arctic regions.