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Current and future zoonotic threats from cats and dogs

by
01 August 2014, at 1:00am

David Grant reports on an informative webinar on parasite control

CURRENT and future zoonotic threats from cats and dogs was the title of an informative webinar presented by Ian Wright at the end of April.

Mr Wright is a practising vet who has developed considerable parasitological expertise by virtue of a master’s degree in the subject and also by his role as a member

of the European Scienti c Counsel Companion Animal Parasites (ESCCAP). He was accompanied by Anthony Chadwick, founder and MD of The Webinar Vet, and the webinar was sponsored by Elanco.

I am relatively new to live webinars but found it to be very easy to participate. Having had a couple of reminders from The Webinar Vet, it just took one click of the mouse and I was in. The experience was virtually the same as being in the lecture hall at a congress except that I was in the comfort of my own home.

The sound was perfect and the PowerPoint presentation was clear. Ian is a very relaxed speaker with a good sense of humour and the hour’s lecture ew by. The subject is potentially vast and Ian decided to concentrate on parasitic zoonoses for much of the talk.

First parasite up for discussion, not surprisingly, was Toxocara canis. He went through the life cycle, familiar to most if not all of us, but then went on to elaborate on the public health aspects. Some 3% of people in the UK are sero-positive for Toxocara. The risk is higher in households with a dog and higher still where there is a litter of puppies.

The consequences of human contagion can be devastating. Of these, ocular infections are perhaps the most well known but visceral and neurological forms are equally important. Thus, the potential danger ranges from loss of sight to CNS problems such as epilepsy. Other covert forms exist but it is not easy to correlate sero positivity with clinical signs.

The true incidence of toxocariasis is unknown as it is not noti able.

Although adults can be infected, it is two to four-year-olds most at risk – a very sobering thought for parents of young children. Embryonated eggs are infectious and it caught my attention that embryonation can take place in the coat of the animal, in addition to the places that we tend to traditionally think of: soil, sand pits and parks, for example.

So how can this disease be prevented? The answers are very simple. These are regular worming of pets, picking up faeces and very good hand hygiene. As a dermatologist I was particularly interested in the role of hand hygiene, as this is so important in the control of multi-resistant bacteria.

It is equally important in parasitological diseases. The eggs cannot be destroyed by disinfectants so removal of them with good old soap and water is what is required.

Regular worming was discussed at length and also in the question and answer session at the end. Worming twice a year is ineffective in controlling this parasite. The bare minimum is four times a year and monthly is to be preferred in higher risk situations – families with children, for example. Puppies should be wormed every two weeks until weaning.

Monthly worming means zero shedding 

In the discussion afterwards, Ian made the point that zero shedding of eggs will be achieved by monthly worming. Surely the way forward was my thought. In terms of products available we are spoilt for choice and consideration should be given to achieving good compliance and therefore an individual owner’s ability to use the products properly. Here, education is the most important factor.

The next parasite discussed was Echinoccus granulosus, a tapeworm that is non-pathogenic in canids but a serious zoonotic risk to humans, which can lead to hydatid cysts. Dogs acquire this parasite from eating infected carcases, mainly sheep. 

The parasite has a well-defined geographical incidence and in these areas vets are well aware of the problem. Advice given is to worm with praziquantel every 4-6 weeks and there is a need to persuade owners of this as hydatid disease in humans is very unpleasant and cases occur every year. Good compliance is essential.

I had forgotten that it is possible to acquire the dog tapeworm Dipylidium caninum. This can occur as a result of the accidental ingestion of fleas, including parts of fleas under the fingernails for example. Once again, regular worming and in this case flea control allied with hand hygiene should prevent human infection.

Hand hygiene was a recurrent theme in this webinar. With a combination of potential problems from multi-resistant bacteria and equally nasty parasites, I would hope that there would be many practice meetings in the weeks after this webinar to hammer home the importance of this.

Giardia and toxoplasma 

Ian moved on to zoonotic protozoan diseases. Those discussed were Giardia and Toxoplasma. With both these diseases there is no chemical prophylaxis. Most important are, as before, good hand hygiene and food and water monitoring.

Giardia in people is often acquired abroad from faecally contaminated food or water. Giardia duodenalis is the pathogen implicated in a wide variety of species including dogs, cats and man. This parasite can be transferred from owner to dog and vice versa. Resistance to fenbendazole is a potential problem, making an accurate diagnosis advisable. There is an ELISA test that is very sensitive.

Along with Toxocara, Toxoplasma gondii is a parasite with a high profile among veterinary practice clients, mainly because of the risk to pregnant women. Cats are the definitive host but shed oocysts only intermittently. The diagnosis rests on identifying oocysts in the faeces, which is difficult, and by a serological test. The problem with this latter test is that it does not necessarily identify active infection.

Apart from acquiring the disease by contact with cat faeces, the disease can occur after eating undercooked meat and fruit and vegetables that have not been washed. The consequences in pregnant women are well known but there are behavioural implications too, with a possible link to a whole range of mental illnesses.

This appears to be a “clever” parasite as it can affect mouse behaviour, for example, to the extent of making cat urine appealing and thus increasing the possibility of a mouse being eaten. The zoonotic risk can be minimised by good hand hygiene, disposal of faeces where possible and ensuring that meat is properly cooked and fruit and vegetables washed before eating. The risk from cats is very much smaller than from contaminated food.

The final part of this webinar looked at future threats. The diseases discussed were rabies, Echinoccus multilocularis and leishmaniasis.

As far as rabies is concerned, 95% of cases worldwide occur in Africa and Asia. It is still endemic in the USA and Canada. Although it continues to be a risk in the EU, numbers of cases have declined considerably.

The same cannot be said for E. multilocularis. This is a serious and significant zoonosis that is spreading west and knocking at the UK shores. The definitive host is the fox and paradoxically success in diminishing rabies cases has favoured fox multiplication, and the red fox is the main risk for spread of this parasite.

It is important to keep tapeworm control in place to minimise the risk of this parasite entering the country, and with relaxation of entry rules veterinary advice prior to leaving the UK is essential. If it were to arrive, praziquental treatment monthly would be required, but in Ian’s words “we would be stuck with it”.

Finally, Leishmania was discussed. Currently, the sand y vector is not present in the UK, although with climate change this could quite quickly alter. At the moment the emphasis is on advice to be given to clients wishing to take their dogs abroad.

There is a Leishmania vaccine which gives approximately 93% protection. Use of insect repellents as collars or pyrethroid products should be added and will reduce the risk further.

Complicated treatment

Although treatment regimes exist, these are complicated and most cases will not be cured, thus posing a continued risk to the owners. The prognosis in the long term is therefore guarded. Clearly, considerable risk is associated with re-homing dogs from endemic areas in southern Europe. The disease in humans is most likely in immune-compromised individuals, in whom it can be fatal.

Current diagnostic methods were outlined, including blood smears, fine needle aspirate of bone marrow and lymph nodes, skin and lymph node biopsy and serological tests. These and treatments were brie y described and perhaps would be best performed by those experienced in the disease. 

I thoroughly enjoyed this excellent webinar but more was to come. Anthony Chadwick, in his very relaxed style and acting as chairman, passed on numerous questions.

This is a major advantage of this form of CPD, compared to a congress lecture. We had 40 minutes of questions and anyone who left the webinar early missed out. And, as Anthony pointed out, nobody would notice if you left early! He also cleverly only mentioned questioners by their first name: no need to worry about asking a foolish question.

Participants were from all over the world from places as diverse as Australia, Egypt, Moscow and most parts of continental Europe as well as the UK.

Finally, Ian left us with two useful websites. It has not been possible to cover here all that was said in the webinar but more detail and guidelines can be found on www.esccap.org and on the BSAVA website www.bsava.com.

Anthony Chadwick, his team and Ian Wright are to be congratulated on a very informative, entertaining and useful webinar – thanks also to Elanco Companion Animal Health.