1. small Anim. Pracr. (1977) 18, 359-364.

‘Are dogs a health menace?’ PETER MCKENZIE

Department of Infectious Diseases, Belvidere Hospital, Glasgow

The dog is an emotive subject. Probably the majority of people in this country like dogs. However, there are many who do not share this affection and who hold the view that the dog is not man’s best friend not least because in addition to the foul- ing of public places it is regarded as a source of infective illness.

My remit is ‘Are dogs a health menace?’ I would like to review the health hazards based on published material and on personal experience as a clinician in a large Infectious Diseases Unit in Glasgow.

TABLE I . The dog in relation to human health hazards

Bites (rabies) Parasites

External : fleas, sarcoptic mange, Cheyletiellu yasguri, ringworm Internal : Toxocara sp., tapeworm (hydatid disease)

Salmonella Leptospira canicola-meningitis Allergy Cause of traffic accidents

Dog bites There is little published evidence on the incidence and severity of dog bites.

D.A. Robinson (1976) reported that in the Liverpool Walton Emergency Accident Unit from November 1974 to October 1975 there were 2064 cases of dog bites and these accounted for 3% of the total attendances. In 92% the lesions were graded as superficial, in 24% the skin was not broken. Only 1/5 cases required one further attendance. The incidence and clinical severity of dog bites seen at the Royal and Victoria Infirmaries in Glasgow in 1975 were completely comparable to the Liver- pool experience. However, there have been isolated cases of savaging, the most tragic in recent times being where guard dogs were responsible for the death of a

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school boy. As the result of this occurrence regulations have been enacted for the stricter control of guard dogs. It is interesting that there is a consistently implied association of a dog bite with tetanus. There is no documented proof of tetanus arising from dog bites but there is little chance of this happening as almost every person bitten by a dog receives tetanus toxoid. However, it is a safe procedure and at least serves to help to maintain the level of tetanus immunization in the community.

Rabies Great Britain is free from rabies firstly because it is an island and secondly

because of its quarantine laws. Rabies is spreading across Europe at the rate of 40 kilometres a year, the fox being the main vector, and is expected to reach the Channel ports by 1980. Every effort must be made to keep Britain free of rabies. My opinion is that any animal found to have been smuggled into the country should be destroyed and the owner should receive a period of imprisonment without the option of a fine.

TABLE 2. Animal susceptibility to rabies*

Extremely high High Moderate

Foxes Skunks Dogs Bats Sheep Cattle Horses

*WHO (1973).

TABLE 3. Confirmed cases of animal rabies

Domestic Wild animals animals

USA (1 969-1 973) Center for Disease Control Skunks 8335 Cattle 1945

Foxes 3442 Dogs 1088 Bats 2018 Cats 845 Raccoons 902 Total 14,717

France (1968-1 975) Centre d'dtudes sur la rage Foxes 7426 Cattle 963

Badgers 138 Cats 306 Others 184 Dogs 213 Total 7748

A R E DOGS A H E A L T H M E N A C E ? 361

What is the extent of the dog’s culpability? The dog’s susceptibility to rabies is considered moderate, see Table 2.

It is apparent that the main vectors are skunks in the USA and foxes in France. In the USA in the 10 year period, 1964-1973 there were ten cases of human rabies and in only two cases were dogs the vectors. So the situation should be viewed with some perspective. If rabies does enter our island, nationwide action will be taken. Appointment of dog wardens will be effective in reducing the number of strays and immunization of dogs in the rabies area will become the order of the day. A trained, immunized dog would be much less a health menace than is feared. If British experience parallels that of the USA, ten cases of rabies (two involving dogs) in 10 years in a population of 160 million, then there should be very few cases here. The clinical course of rabies is somewhat horrific but no worse than that from respiratory poliomyelitis or tetanus. Indeed, the combined morbidity from immunization and mortality from rabies will be minute compared with the annual holocausts due to lung cancer, death on the roads and the insidious devasta- tion of alcoholism.

Parasites External. Fleas, Cheyletiella and sarcoptic mange (dog scabies) can all give

rise to intense itching in the human. However, these animal parasites do not be- come established on the human skin. All are temporary invaders and if the dog is recognized as the culprit and the appropriate insecticide is applied to the dog, the parasites are dealt with at source and no further bites occur.

Ringworm transmission from dogs can occur but it is uncommon.

Internal Toxocara canis. There has been a great deal of publicity of the dangers of

Toxocara infection in humans, the problems having been highlighted by the work and reports of Professor Woodruff. It was valuable that the routes of infection and the methods of prevention should be brought to the notice of the public. Since the first publications the whole matter has now fallen into perspective. Bitches, at the time of parturition, and young puppies excrete the eggs of Toxocara in their faeces. Skin testing reveals evidence of previous infection in 2% of the human population but overt disease of the eye, liver and nervous system is rare. In effect evidence of previous infection is high but evidence of clinical disease is low. As Woodruff indicated Toxocara infection is entirely preventable by assiduous worming of dogs-especially puppies in the first 6 months of life. Woodruff also highlighted the problem of fouling of pavements and public parks by dog faeces. While it is a comparatively minor medical hazard, from an aesthetic point of view the practice is objectionable and wholly indefensible.

Hydatid disease Echinococcus granulosus. This tapeworm occurs as a bladder-like cyst in sheep and

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the dog becomes infected by feeding on the carcases or on sheep offal. When humans become infected the larvae develop into hydatid cysts in the liver, lung or brain. There is a relatively low incidence in this country. The Public Health Laboratory Service reports that in the period 1967-70 there were thirty cases in the UK and Eire. Hydatid disease is entirely preventable by regular worming of dogs. In addition the opportunity for dogs to feed on infected material should be avoided by the burying or removal of dead sheep and the cessation of providing sheep’s offal as a dog food.

Salmonella Salmonella organisms have on occasion been isolated from dog faeces. The in-

fection has probably been acquired from infected raw meat or offal. There is little evidence of salmonella infection in humans having been acquired from dogs.

Leptospira canicola infection This disease involves the kidneys and is usually spread by the urine of infected

animals, the organism entering through breaks on the skin or mucous membranes. It is fairly widespread in dogs, especially strays which have not been immunized. The main manifestation in human beings is meningitis. If this is treated with peni- cillin there is no mortality. The incidence of Leptospira canicoZa meningitis in the West of Scotland in the 1950s was three or four per year but the Communicable Diseases Scotland Unit reports only six cases for the whole of Scotland for the 5 year period 1971-75. This is probably due to the increasing number of dogs being immunized.

Allergy Allergic manifestations due to the dog are also uncommon. However, if a dog

is the cause of florid urticaria or asthma then there is no option but that the dog must go from the home involved.

Accidents attributable to dogs In the Strathclyde Region of Scotland (which contains half the total population)

in 1975 there were 1713 accidents claimed to be attributable to dogs. There was personal injury to thirty-six, of which thirty-three were slight and three were regarded as slightly more serious. Many of the accidents occur in the middle of the night and the dogs are never traced. Obviously uncontrolled dogs can cause accidents but the number for which dogs are blamed is probably in excess of the true incidence.

Having looked at the individual hazards to humans for which dogs can be responsible the question remains ‘Is the dog a menace to health?’

A trained and controlled dog, which in effect is an obedient dog, is less liable to bite and is unlikely to be the cause of road accidents compared to the uncontrolled stray.

A R E DOGS A H E A L T H M E N A C E ? 363

Inoculation and regular worming (especially in the first year and under the super- vision of a veterinary surgeon) prevents the occurrence in humans of leptospiral meningitis. Toxocara and hydatid disease. The nuisance value of the external para- sites can be dealt with by the awareness of the medical practitioner or the veterinary surgeon or preferably by their joint collaboration. So at the present time (excluding rabies) a trained, controlled dog which has been inoculated and wormed is not a health menace of any importance. It is also an interesting observation that small animal veterinary surgeons and dog breeders have no higher incidence of infective illness than other members of the community.

Having established that a trained, inoculated and wormed dog is essentially no menace to health it might be salutary to look at the dog’s contribution to the general welfare and health of the community. The list is impressive (UK): guide dogs for blind, 2300; farm and sheep dogs, 50 000 + ; police dogs, 1818; security services, 1056; dogs used in research, 16 195.

The contribution of a guide dog to a blind person needs no elaboration and by the same token to observe a shepherd and a sheep dog at work is to see the ultimate in collaborative skill and achievement. While the subject of dogs being used in experimental research is controversial there is no doubt this provides the oppor- tunity for acquiring basic operative skills in cardiac surgery and knowledge of the pharmacological action of new drugs.

Finally to so many families and especially to older people living alone the dog gives companionship and protection. This contribution to the health and well being of the community cannot be computed but it is undoubtedly immense.

REFERENCES

Dog bites ROBINSON, D.A. (1976) Dog bites and rabies: an assessment of risk. Brit. Med. J. 1, 1066. Dog bites. Glasgow Royal Infirmary Casualty Department (1975) J.D. Macfarlane and A.M.

Dog bites. Casualty Department, Victoria Infirmary, Glasgow (1 975) W. Thomson, personal Murray, personal communication.

communication.

Rubies WHO Expert Committee on Rabies (1973) W.H.O. Tech. Rep. Ser. No. 523. WHO (1975) World Survey of Rabies XVI. Rabies. Office of Health Economics (1976).

Injestations LYELL, A. (1972) Pet animal infestations. Scot. Med. J . 17, 334. ALEXANDER, J.O’D. Glasgow Royal Infirmary, personal communication.

Toxocura WOODRUFF, A.W. (1970) Brit. Mrd. J. 3, 663. Bolo, O.A. & WOODRUFF, A.W. (1973) Brit. Med. J. 4, 470.

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HOLT P.E. (1976) Vet. Rec. 98, 383 . GIRDWOOD, R.W.A. Personal communication.

Leptospirosis Leptospira canicola. Communicable Diseases Scotland Unit (1976) Personal communication.

Accidents attributable to dogs Mr Elphinstone Dalgleish, Deputy Chief Constable, Strathclyde Region, personal communica-

tion.

Hydatid disease Public Health Laboratory Service, Communicable Diseases Report 72/48.