Tapeworms of UK cats and dogs: an update

26 November 2013
Clinical
10 mins read
02 November 2013
Volume 4 · Issue 9

Abstract

Tapeworms (class Cestoda) remain common parasites of UK cats and dogs despite widespread use of anthelmintics by pet owners. Although this group of helminths rarely causes disease in the definitive host their presence often causes distress in pet owners and some species have zoonotic potential. Echinococcus granulosus remains a serious endemic zoonosis despite repeated campaigns to eliminate it. This article reviews the epidemiology of tapeworm infections in the UK, zoonotic risk and the role of veterinary nurses in advising the public, diagnosis, treatments and control of these parasites.

Tapeworms are helminths belonging to the class Cestoda and are common parasites of cats and dogs. Cestodes consist of a head bearing hooks or suckers to attach to the intestinal wall, a short unsegmented neck and a chain of segments called proglottids. Taenia spp. and Dipylidium caninum are large tapeworms of cats and dogs and remain ubiquitous throughout the UK despite the use of cestocidal anthelmintics being a widespread practice. Visible motile proglottids are passed in the faeces but will also actively crawl out of the anus. The visible nature of these proglottids often leads to revulsion and concern in pet owners leading to the seeking of veterinary advice and nurses will often be called on to dispense advice on treatment and control, as well as allaying fears among members of the public regarding zoonotic risk. Echinococcus granulosus is a closely related tapeworm of canids but is only a few millimetres long in the definitive host. It is a serious zoonosis and despite extensive attempts to control it, endemic foci in the UK remain. This article provides an update on the distribution, diagnosis, treatment and control of these parasites.

Life cycle

Tapeworms of cats and dogs have a complex life cycle, requiring an intermediate host. The adult tapeworm is found in the intestine, attached to the intestinal wall. Eggs or proglottid segments containing eggs are passed in the faeces and ingested by the intermediate host. This leads to cyst formation in the tissues and it is these cysts that are then infective (usually through scavenging or predation). The details of the life cycle vary depending on the species of tapeworm involved but important examples are:

  • Taenia spp. — the adult tapeworms are large (up to 500 cm) in length and cats and dogs become infected by ingestion of tissue cysts in sheep, rabbits and rodents. This occurs through scavenging or hunting. Taenia ovis cysts in sheep remain a significant cause of meat condemnation in sheep
  • D. caninum — the adult tapeworm is smaller (up to 50 cm) and fleas such as Ctenocephalides felis (Figure 1) and lice act as intermediate hosts. Infection occurs either by grooming or by ingestion of infested prey (Figure 2).
  • E. granulosus — canids harbour small adult tapeworms (5–6 mm long). Ruminants, pigs and man may all act as intermediate hosts with the formation of hydatid cysts. These can lead to offal condemnation in farm animals, but more seriously can lead to significant pathology in man with cysts forming in the bone, liver, central nervous system and heart. Ingestion of the cysts by canids occurs mostly through scavenging of carcasses or feeding of offal.
    • Figure 1. Ctenocephalides felis.
    Figure 2. Dipylidium caninum lifecycle.

    Geographical spread and public awareness

    Prevalence data on tapeworm infections in domestic cats and dogs are scarce as egg counts are unreliable for detecting tapeworm infections and post mortem prevalence studies are lacking. The differing nature of the intermediate hosts required for the three genera of tapeworm found in UK cats and dogs affects their epidemiology and the pets at risk of infection.

  • Taenia spp. — these are found throughout the UK in rodent, lagomorph and livestock intermediate hosts. Cats are frequently infected through hunting and dogs through scavenging and predation. Feeding of offal and undercooked meat is also a common practice, especially in working dogs and these dogs are also seasonally more likely to be exposed to carcasses from livestock in the case of farm dogs and from shooting in the case of gun dogs.
  • D. caninum — is also found throughout the UK and prevalence is linked to the frequency of outdoor exposure to fleas and the control of indoor flea populations. As a result, infections are most common when flea control programmes breakdown or are not in place. Cats however, are fastidious groomers and as a result will rapidly groom off fleas that they come into contact with outdoors. This means that infection can persist in outdoor cats even if adequate flea protection is in place. Although lice can also transmit this parasite, significant lice infestations are uncommon where sufficient flea control measures are being used.
  • E. granulosus — pockets of endemic foci remain in the UK where dogs have access to carcasses of ruminant livestock. Herefordshire, Mid Wales and Western isles of Scotland have the highest prevalence and the remote nature of some of these locations can make the clearance of potentially infected carcasses very difficult.

    • It is important for veterinary nurses and surgeons to recognise that D. caninum is a potential zoonosis as well as E. granulosus but in the case of D. caninum humans act as the definitive host with adult worms in the small intestine. While infection in people is rare and the pathogenicity low, there can be significant distress associated with tapeworm infection. Cases in the literature have been reported in recent years from Poland (Szwaja et al, 2011) and in Japan (Tsumura et al, 2007) with excellent response to praziquantel treatment. It is an essential role of the veterinary nurse to inform people of zoonotic risk, but also to reassure the public and make sure accurate advice is given. In the author's experience pet owners are often more willing to share these concerns with nurses away from a consult. People concerned they may be infected with D. caninum should be assured that infection is uncommon and responds well to treatment but is a possibility in mixed worm infections or if proglottids have been seen in the faeces.

    Diagnosis

    Diagnostic approaches in the definitive host differ between E. granulosus and other tapeworm infections found in the UK.

  • Taenia spp. and D. caninum — infection is evident from proglottids in the faeces or on the coat around the perineum. D. caninum (Figure 3) may be differentiated from Taenia spp. (Figure 4) by the more elongate shape of the proglottids and the presence of double genital organs, visible with a hand lens (Figure 5). The proglottids may also be broken up with a needle in water and examined under the microscope. In the case of D. caninum, egg packets will be seen, whereas Taenia spp. proglottids will contain numerous single eggs. This a technique that can easily be carried out by veterinary nurses and technicians in the first opinion practice setting. These egg packets and eggs are not commonly seen on faecal flotation tests and this is a relatively insensitive method of diagnosis (Wolfe et al, 2001).
    Dipylidium caninum.Courtesy of Bayer
    Taenia taeniformis.Courtesy of Bayer
    Dipylidium caninum proglottids.Courtesy of Bayer
  • E. granulosus — the gold standard for diagnosis in canids remains examination of the intestines at necropsy by sieving intestinal contents, scraping the intestinal wall and then examination for the adult parasites (Deplazes and Eckert, 1996). Adult E. granulosus worms (Figure 6) found at necropsy or expulsed after treatment are normally 5–6 mm long with a scolex and 2–3 segments. Examination at necropsy is highly sensitive and specific in experienced hands but is expensive, requires extensive safety precautions and cannot be used in the live dog. Diagnosis in the live pet is problematic as adverse clinical signs are rare and proglottid segments are rarely seen in the faeces. Ova detection in faeces by faecal flotation is also a relatively insensitive method of detection (Wolfe et al, 2001) and if seen, the eggs are typically taeniid in appearance and so do not confirm E. granulosus diagnosis. Therefore, in E. granulosus endemic areas taeniid-infections based on egg detection should be handled as potential E. granulosus infection. Coproantigen enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) tests have been developed to try and provide more sensitive faecal diagnostic techniques. Christofi et al (2002) found ELISA coproantigen testing to have a sensitivity of 83% and a specificity of 98%, dropping to 80% when Taenia spp. infection was also present. PCR antigen testing faeces has also shown to be highly sensitive and specific and has potential for screening programmes in the future (Abbasi et al, 2003). The difficulty in diagnosing infection in individual cases however, makes prophylactic treatment the safest option in endemic areas.
    • Figure 6. Echinococcus granulosus.

    Treatment

    All tapeworms of veterinary significance are exquisitely sensitive to praziquantel and this remains the treatment of choice in cats and dogs. A dose of 5 mg per kg orally in cats and dogs or 8 mg per kg as a spot on solution in cats is sufficient to eliminate infection. Where dogs are infected with Echinococcus species, it is advisable that they are treated under the supervision of a veterinarian and that the dogs are shampooed to remove any parasite eggs adhering to the coat. Fenbendazole has a NFA-VPS status (may be supplied by any registered qualified person (RQP) — a veterinarian, a pharmacist or an appropriately qualified SQP provided the requirements for supply are met) and is effective at treating Taenia spp. It also has 60–70% efficacy against D. caninum. A dose of 50 mg/kg orally is required in cats and dogs. Praziquantel can be given in formulations on its own (Bob Martin dewormer®, Bob Martin (UK) Ltd, Droncit®, Bayer) and has an AVM-GSL status (over the counter). However, it is also found in combination with a variety of other drugs. When combined with pyrantel, febantel or oxantel to include roundworm activity then its status is NFA-VPS but when combined with milbemycin oxime (Milbemax®, Novartis) then this is upgraded to prescription only medicine–veterinary (POM-V) status. It can be seen that in most of its formulations praziquantel can be dispensed by veterinary nurses and suitably qualified persons (SQPs), but an owner's requirement for control of other worms such as Toxocara spp and Angiostrongylus vasorum as well as tapeworm should be taken into account when dispensing treatment advice. It is increasingly the veterinary nurse's role to inform the public of different worming product combinations in relation to the client and pet's needs even if this may require the use of POM-V products.

    Control of tapeworm infections

    Tapeworm control requires:

  • Chemical prophylaxis — Taenia spp. have a prepatent period of 4–10 weeks and D. caninum 3 weeks. This 3 week pre-patent period only occurs under optimum conditions of humidity and temperature for the intermediate host and so use of a monthly product containing praziquantel, often in combination with a monthly round wormer to eliminate Toxocara spp. egg production will be sufficient to eliminate proglottid shedding. The list of products that fulfils this portfolio is now very large but any praziquantel containing product will be effective. It is the role of the veterinary nurse to ensure that any round wormer used in combination is effective against at least patent Toxocara spp. infection. This is summarised in Table 1 below.
  • Avoiding ingestion of infective stages in the intermediate host — in the case of Taenia spp, avoiding carcass scavenging, the feeding of raw offal, undercooked meat and active hunting of wild rodents and birds is required. The feeding of offal to kennelled and working dogs is a particular risk factor as is the hunting season in working gun dogs where there is increased exposure to potential prey and scavenging opportunities. It can be practically impossible to avoid exposure to the parasite in these dogs and as a result chemical prophylaxis is very important where heavy burdens can develop. This is also true in outdoor cats where hunting behaviour is common. Conversely, indoor cats and dogs not exposed to these potential sources of infection do not require chemical prophylaxis. Although resistance to praziquantel is not recognised in tapeworm infections of companion animals due to the large wildlife reservoir both in feral cats, foxes and intermediate hosts, praziquantel prophylaxis in pets not being exposed to infection cannot be justified.
  • Flea and louse control — fleas and lice on cats and dogs act as intermediate hosts for D. caninum and controlling their numbers in household and kennel situations forms an important part of the control of this tapeworm. In outdoor cats that will rapidly groom off adult fleas they come into contact with it is unlikely that flea prophylaxis alone will control the parasite and prevent proglottid excretion. It may however be sufficient for prevention of zoonotic transmission.
  • Picking up of faeces — this will help to reduce exposure of livestock to Taenia ovis and E. granulosus eggs.

    • Product Monthly use prevents Toxocara spp. egg shedding Licensed to treat hookworm infection Licensed to prevent Angiostrongylus vasorum Licensed for monthly Dirnfilaria immitis infection oral or spot on
    Pyrantel yes yes no no oral
    Febantel yes yes no no oral
    Oxantel yes yes no no oral
    Milbemycin oxime yes yes (accept Uncinaria stenocephala) yes yes oral
    Emodepside yes Yes (accept Uncinaria stenocephala) no no Spot on

    The pre-patent period of E. granulosus is 6 weeks and so transmission to canids can be broken by treatment with praziquantel at least every 6 weeks and the prevention of access of dogs to offal and carcasses from cattle and sheep. These methods are theoretically very achievable to implement and so there have been numerous attempts to eradicate the parasite from the UK. Between 1974 and 1983 there were two cases of human hydatid disease in Wales and 0.2 cases per million in the rest of the UK. A voluntary control programme of supervised praziquantel dosing of dogs in Wales reduced this incidence and this was replaced by a health education programme in 1990. In 2001 the foot and mouth epidemic proved a setback in hydatid disease control as more carcasses were easily available to dogs to scavenge. This led to an increase in prevalence of E. granulosus in Welsh dogs from 3.4% in 1993 to 8.1% in 2002 (Buishi et al, 2005). Since then the number of annual cases of human hydatid disease in the UK has remained fairly constant with 12 cases in 2011. The Welsh assembly continues to raise public awareness of the disease and promotes praziquantel worming programmes in dogs.

    In the case of the zoonotic transmission of E. granulosus and D. caninum, good hygiene forms an additional level of control and veterinary nurses should emphasise this to all pet owners to help prevent a wide variety of zoonoses transmitted by the faecaloral route. This can be performed at puppy consults, weight checks, geriatric checks and whenever general health advice is sought. The fur of pets may become contaminated with faeces and therefore be a potential route for E. granulosus, Giardia spp., Toxoplasma gondii, Campylobacter spp. and Toxocara spp. transmission to people (Wolfe and Wright, 2003). In the case of D. caninum, flea and lice body parts may become trapped under fingernails and then transmitted orally.

    Key points

  • Tapeworm infections remain common in UK cats and dogs.
  • Areas of endemic foci of Echinococcus granulosus remain in the UK despite extensive attempts to eliminate it. This parasite represents a serious zoonotic risk to dog owners in these areas.
  • Veterinary nurses continue to be vital in giving accurate advice in tapeworm control programmes as well as providing diagnostic and treatment expertise.
  • This article provides an update on the distribution, diagnosis, treatment and control of these parasites.

    • Conclusions

    Tapeworm infections remain common parasites of domestic cats and dogs and although they are of minimal pathogenicity in these hosts they are a source of concern to owners and D. caninum and E. granulosus have zoonotic potential. Exposure to these parasites increases seasonally with increased hunting activity and flea exposure of cats during the summer months and working gun dogs having increased exposure during the hunting season. As well as recognising and diagnosing infection, nurses are required to ascertain whether the lifestyle of pets puts them at risk of tapeworm infection, to give advice to minimise this risk and to advise tapeworm prophylaxis where required. It is also the role of everyone in the veterinary profession to alert people to the zoonotic risk that tapeworm infection in pets represent but also to put this risk in perspective. This is vital in E. granulosus endemic areas and the importance of hygiene among pet owners and those working with dogs and dog faeces must also be emphasised.

    tapeworm
    Taenia
    Dipylidium caninum
    Echinococcus granulosus
    treatment
    control