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A | Toxocara spp. (ascarids) and Hookworm |
| B | Echinococcus spp. |
| C | Heartworm (Dirofilaria immitis) |
Ascarid and hookworm infection occur across Europe, whilst the distribution of the other infections is geographically related. By adding Echinococcus spp. and/or heartworm control to an ascarid and hookworm control plan, basic control plans can be produced for dogs and cats anywhere in Europe. Appropriate anthelmintic treatment for that parasite can then be identified and the animals treated at suitable intervals. More detailed considerations for each of the key parasites can be found below. Control of other parasites, such as lungworms and the French heartworm (Angiostrongylus vasorum) (Tables 1 - 4) which may be important in particular areas, should be added as necessary according to need.
A Toxocara spp. and Hookworm
Puppies can be severely infected by these intestinal worms in utero or via nursing and these may cause serious illness, before diagnosis is possible by faecal examination. For this reason, puppies should be treated with appropriate anthelmintics normally starting when puppies are 2 weeks of age, with treatment repeated according to data sheet indications. Because prenatal infection does not occur in kittens, fortnightly treatment can begin at 3 weeks of age, repeated at 5 and 7 weeks or according to data sheet recommendations. Nursing bitches and queens should be treated concurrently with their offspring since they may develop patent infections along with their young.
Toxocara spp. infection can occur in older dogs and cats, and as it is extremely unlikely to be associated with clinical signs in older animals, it is difficult to tell whether a dog is infected unless regular faecal examinations are conducted. In addition, these parasites are fecund egg-layers and just one or two worms can produce large numbers of eggs. Therefore continued regular treatment of dogs and cats is appropriate using a suitable anthelmintic if regular diagnostic testing is not instituted (see next paragraph). An anthelmintic with a broad or narrow spectrum of activity can be chosen according to the risk of other worm infections. As the pre-patent period for Toxocara spp. is a little over four weeks, monthly treatment will minimise the risk of patent infections and can be recommended in high risk scenarios such as the pet living in the family with small children and common use of a garden (or similar). Annual or twice annual treatments have been shown not to have a significant impact on preventing patent infection within a population, so a treatment frequency of at least 4 times per year is proposed as a general recommendation.
Where an owner chooses not to use anthelmintic treatment regularly then monthly or 3 monthly faecal examination may be a feasible alternative. Faecal examinations should be performed using at least 3 to 5 grams of faeces and modified McMaster or other flotation technique, associated with other methods (such as direct exam, stained smear or sedimentation) (Tables 5 - 6) as needed.
B. Echinococcus spp.
B. Echinococcus spp.
Both Echinococcus granulosus and Echinococcus multilocularis are zoonoses of major public health concern. In areas where Echinococcus granulosus (including the equine and bovine genotypes recently proposed as species E. equinus and E. ortleppi) is endemic (Fig. 1) dogs that may have potential access to carcases or raw viscera especially from sheep, pigs, cattle or horses (depending on the Echinococcus genotypes) should be treated at least every 6 weeks with an effective compound containing praziquantel or epsiprantel.
Fig 1 Distribution of Echinococcus granulosus in Europe
In the Central and Eastern European endemic area of Echinococcus multilocularis (Fig.2) with red foxes as main definitive hosts and voles as intermediate hosts, dogs that have access to rodents should be treated at four weekly intervals with an effective anthelmintic containing praziquantel or epsiprantel. Cats, in contrast to dogs, are thought to be of minimal zoonotic risk as they are poor hosts for this worm.
Fig. 2 Distribution of Echinococcus multilocularis in Europe
Specific diagnosis of Echinococcus infections in definitive hosts is difficult as the taeniid-eggs cannot be differentiated morphologically. Coproantigen tests are not available commercially and PCRs enabling species and /or genotype identification are performed in specialised laboratories only. Therefore, in Echinococcus endemic areas taeniid-infections based on egg detection should be handled as potential Echinococcus infection. Where animals are infected with Echinococcus species it is advisable that they are treated on two consecutive days with a highly efficient compound under supervision of a veterinarian and the animal should be shampooed to remove parasite eggs adherent to the coat using suitable protective clothing such as protective gloves and mask for the personnel involved.
C Heartworm
Heartworm infection (Dirofilaria immitis) and subcutaneous dirofilariosis (D. repens) are endemic in many south and eastern European countries (Fig. 3). Climatic changes favourable to parasite development and the increasing number of pets who travel have increased the risk of infection for dogs and cats. Heartworm infection can be life threatening to dogs and cats.
Fig. 3 Distribution of Dirofilaria immitis and Dirofilaria repens in Europe
C.1. Dirofilaria immitis - Dog
Presently there are no repellents/insecticides that have been demonstrated to disrupt transmission of heartworm, therefore control depends on the use of heartworm preventatives that kill the young heartworm prior to their migration towards the heart. Using appropriate products adult heartworm can be effectively prevented. In most parts of Europe where infection is endemic, the transmission season of heartworm infection generally lasts from April to October. In the Canary Islands infection can be transmitted throughout the year. For products that are administered once a month, the treatment must begin within 30 days following the estimated season onset of transmission and be continued until 30 days after the period has ended. An injectable product exists that is able to protect dogs for a year following a single injection.
Puppies and kittens have to be placed on preventive heartworm treatment as soon as possible after birth (consistent with label recommendations).
In areas at risk for heartworm infection, adult dogs should be tested for circulating microfilariae and heartworm antigen before starting preventive treatment for the first time. Annual retesting will ensure that preventive treatment, including owner compliance, are adequate.
C.2. Dirofilaria immitis - Cats
Although cats are susceptible hosts for heartworms, they are more poorer hosts for this infection than are dogs. Furthermore, feline heartworm infection is more elusive to diagnose than in dogs and can be easily missed due to the different behaviour of heartworms in this host.
Cats living in canine heartworm endemic areas frequently become infected but parasites do not develop to the adult stage. Furthermore, most heartworm infections in cats are light and consist of 1-2 adult worms, often of the same sex. Consequently, microfilaremia is absent. If present, microfilaremia lasts only a few months and the life span of adult parasites is quite short. As a consequence, tests for circulating microfilariae have poor/very poor diagnostic value in cats. Antigens and antibody tests can be used but often have to be repeated because of either low sensitivity (antigens) or low index of suspicion of adult heartworm infection (antibody). A definite diagnosis of heartworm infection can often be obtained only by the application of haematological and serological test in conjunction with thoracic radiography and echocardiography.
Testing cats before administration of anthelmintics or re-testing during preventive anthelmintic treatment is recommended. However, if an antibody test is used, it might show a positive result in sensitised animals exposed to 3rd-4th stage larvae: it will demonstrate that the cat is exposed to a heavy risk of infection and reinforces justification for recommending prevention. Since microfilaremia in cats is uncommon, transient if present and below concentration levels that might trigger an adverse reaction to microfilaricidal preventive drugs, pretesting for microfilariae is unnecessary in healthy cats.
C.3. Dirofilaria repens
D. repens can infect both dogs and cats. Most infections are asymptomatic, though cold, not painful nodules containing the adult parasites can be found on the skin surface of infected animals. Seldom, in case of heavy infection or in sensitised animals, light to severe dermatitis can be observed. Most cases of zoonotic Dirofilaria infections in Europe are caused by this species. Like D. immitis, D. repens infection results in microfilariae in the circulation. It is important to determine whether microfilariae are those of D. immitis or D. repens (see Table 6).
C.4. Comments
Most heartworm preventative anthelmintics have the potential to control a range of other worms and so an appropriate product may be chosen to control other nematodes and cestodes as necessary. In addition, treatment can be extended throughout the year to ensure the continued control of non-seasonal parasites such as Echinococcus spp. and Toxocara spp., where necessary.
II.2. Diagnosis
Patent infections of all of the worms mentioned can be identified by faecal examination, except for D.immitis (heartworm) where a blood sample is examined for microfilariae, antigens or antibodies (Tables 5 and 6). Faecal examination for worm eggs can be carried out using a modified McMaster or other flotation technique (Tables 5 and 6). The scale of the worm burden can be crudely estimated from the number of eggs present in the sample. However, it should be noted that for ascarids such as Toxocara, a negative correlation between fecundity and number of adult worms has been reported.
Where larvae are produced, samples can be examined using the Baermann technique (Tables 5 and 6). Repeat samples can be examined approximately 7 - 10 days after treatment to check that treatment has resulted in the removal of the worm infection.
Where it is important to minimise any infection risk and preventative treatment is not chosen then monthly faecal examinations may be a suitable alternative.
II.3 Resistance
There are few documented case reports of anthelmintic resistance in dogs and cats, and fewer where the case has been well investigated. Apparent low incidence may be associated with low frequency or absence of resistance. At present there is no way of detecting anthelmintic resistance in dogs or cats other than the faecal egg-count reduction test. It is desirable that more sensitive tests including molecular techniques are developed to allow monitoring of continued efficacy.
Traditional anthelmintic treatment of dogs and cats has always left many parasite stages outside the host that are unselected by treatment of the dog or cat. If the frequency of anthelmintic treatments increases then this could increase the selection pressure on parasites, most likely to result in resistance in the case of the kennel situation where simultaneous treatment of a group of dogs with the same product might result in a high selection pressure. It is therefore recommended that careful consideration should be given to worm control programs for dogs in a kennel situation and it is recommended that faecal monitoring is regularly conducted to identify worm species present and the effectiveness of any control program.
In the absence of evidence to the contrary, it is logical to assume that the risk of resistance developing is proportional to the exposure of the parasite population to specific drugs. Therefore strategies that avoid excessive or unnecessary worming are likely to select less strongly for resistance, and risk-based rather than blanket strategies are justified.
III. Environmental control of parasite transmission
Control of parasite stages (eggs, larvae) in the environment is essential to minimize the infection pressure to humans (zoonosis) or animals. Parasitic contamination of the environment can occur in a number of ways, including excretion of parasitic stages in the faeces and the release of cestode proglottids. Furthermore, environmental infection pressure of dog-transmitted parasites can be maintained by wild foxes and stray dogs in both rural and urban areas, and feral and wild cats can similarly form a reservoir of feline infection.
Most of environmental parasite stages are highly resistant (for month to years). Freshly excreted stages for many parasites can be directly infective (Taenia and Echinococcus eggs). Other parasites require anything from a few days to a few weeks (eggs of nematodes) at appropriate temperatures above 16°C. Therefore, appropriate disposal of faeces is recommended. This should be on a daily basis and should not be flushed down the toilet or disposed of in compost. Infections in intermediate or paratenic hosts may result in prolonged survival in the environment eg birds, rodents, slugs and snails.
Leash laws and faecal cleanup laws especially for urban areas should be enforced. Legislation to control stray dogs and wild cat populations should also be enforced. Other measures to facilitate faecal removal, such as provision of disposal bins and bags should be encouraged. As it is difficult to control where outdoor cats defaecate, particular attention should be given to worm control in cats.
It is most important to prevent initial parasite environmental contamination with comprehensive parasite control programs which have to be designed based on the local epidemiological knowledge. Parasitized animals should be rigorously treated to prevent environmental contamination and monitored, where necessary, by faecal examination to confirm treatment efficacy.
All eggs of cestode and nematode worms are highly resistant in the environmental and may persist in the soil for months or years. For highly contaminated areas, extreme measures are needed for decontamination, including removal of sand or soil or covering the soil with concrete or asphalt (for example in highly populated kennels). Therefore, for kennel or animal homes strict treatment and quarantine of new entrants is required to avoid introduction of infected animals. Children's playgrounds should be well fenced to prevent entry of animals including cats. Sandboxes should be covered when not in use. Sand should be replaced regularly, e.g. once or twice a year. Dessication and ultraviolet light exposure are detrimental to worm eggs so allowing access of sunlight and drying to contaminated areas can assist in reducing the level of contamination.
IV. Owner considerations in preventing zoonotic diseases.
Important preventive measures for pet owners include:
- practicing good personal hygiene;
- controlling pet parasite infections through repeated treatments and/or regular diagnostic testing;
- preventing infection by reducing where ever possible the pet from acquiring infection;
- cleaning up pet feces regularly to reduce environmental contamination with infective parasite stages;
- minimizing exposure of children in particular to potentially contaminated environments.
People in contact with animals that may transmit zoonotic parasites should be advised of the risks and made aware that health risks generally increase by pregnancy, underlying other illnesses and immunosuppression. This information should be made available through physicians and veterinarians at anybodies request without obtaining a medical history of the client and his/her family.
In this respect special care should be taken in case of:
immunocompromised individuals such as:
- pregnant women
- elderly people
- people with HIV-infection
- patients undergoing chemotherapy, organ transplantation, or treatment for autoimmune diseases
- diabetics
other susceptible groups:
- babies and toddlers
- mentally disabled persons
- people with specific occupational risks
V. Staff, pet owner and community education.
Protocols for the control of parasitic infection should be communicated to veterinary and para-veterinary staff and consistently applied. Awareness of parasitic zoonoses, including clinical manifestations in people and particularly children should be created in the medical profession through information brochures. Cooperation between the medical and veterinary profession should be initiated and its benefits underlined in case of zoonoses.
Pet owners should be informed about the potential health risks of parasitic infection, not only to their pets but also to family members and all people living within the action radius of their pets. Brochures in veterinary practices, pet shops, posters or specific websites are useful tools to achieve this. Regular deworming or joining "pet health-check programmes" should be made clear to the general public (e.g. by wearing clear coloured fobs associated with a calendar year). Responsible dog and cat ownership can remove public health concerns.
Additional information and resource materials can be obtained at www.esccap.org
Further Reading
Buijs J., Borsboom G., Renting M., Hilgersom W.J.A., van Wieringen J.C., Jansen G., Neijens J., 1997. Relationship between allergic manifestations and Toxocara seropositivity: a cross-sectional study among elementary school children. Eur Respir J 10 1467-1475
Deplazes P. and Eckert J., 2001. Veterinary aspects of alveolar echinococcosis - a zoonosis of public health concern. Veterinary Parasitology 98 65 - 87
Eckert J. and Deplazes P., 2004. Biological and clinical aspects of echinococcosis, a zoonosis of increasing concern. Clinical Microbiology Reviews. 17 107 - 135
Kapel, C.M.O., Torgerson, P.R. Thompson R.C.A. and Deplazes, P. 2006. Reproductive potential of Echinococcus multilocularis in experimentally infected foxes, dogs, raccoon dogs and cats. International Journal for Parasitology 36 79-86
Sager H., Steiner Moret Ch., Grimm F., Deplazes P., Doherr M.G., Gottstein B., 2006. Coprological study on intestinal helminths in Swiss dogs: temporal aspects of anthelmintic treatment. Parasitol Res 98 333-338
Simon F and Genchi C, (editors) 2001. Heartworm infection in humans and animals. Acta Salmanticensia, Spain
Holland CV and Smith HV (editors), 2006. Toxocara: the enigmatic parasite. CABI Publishing, Wallingford, UK
Table 1A: Characteristics of major worms and protozoa of dogs in Europe: Intestinal roundworms (nematodes)
Table 1B: Characteristics of major worms and protozoa of dogs in Europe: tapeworms (cestodes)
**: There are different strains: sheep strain, cattle strain = E. ortleppi, horse strain = E. equinus, pig-, cervid- and other strains
Table 1C: Characteristics of major worms and protozoa of dogs in Europe: non-intestinal roundworms (nematodes)
Table 1D: Characteristics of major worms and protozoa of dogs in Europe: protozoa
Table 2: Risk factors for major worms and protozoa for dogs in Europe
Table 3A: Characteristics of major worms and protozoa of cats in Europe: roundworms (nematodes) and tapeworms (cestodes)
Table 3B: Characteristics of major worms and protozoa of cats in Europe: protozoa
Table 4: Risk factors for major worms and protozoa for cats in Europe
Table 5: Worm infection of dogs: main clinical signs and diagnosis
Table 6: Worm infection of cats: main clinical signs and diagnosis
