,
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I
279
Toxocariasis in Perspective
A. J.
N
HIS
paper
Relationship meeting
on
BLOWERS,
Domestic
to Human Disease
Pets
and
presented
J.P., A.I.M.L.S., A.I.S.T., F.R.S.H.
their at a
of the Royal Society of Health in January 1967, Hodgman’ referred to the fact that the importance of Toxocara canis, though recognized in 1947, had &dquo;only just hit the headlines&dquo;.
Woodruff2 in the 1970 Watson Smith lecture on Toxocariasis to the Royal College of Physicians, mentioned the paucity of information available on the relevance of the parasite to modern medicine. Later, in the 3 same year, Brown3 reviewed the literature which included reports on 245 affected patients throughout the world. The subject came very much to the public notice in June 1975 when a television programme dealing with the system of catching stray dogs in America, gave a somewhat alarmist viewpoint on Toxocariasis. Since then it has been given particular attention by those concerned with public health. THE DISEASE IN MAN VISCERAL TOXOCARIASIS (visceral larva migrans) occurs when embryonated eggs of Toxocara canis or Toxocara cati are ingested by man. Larvae emerge from the eggs in the human intestine and after penetrating the bowel wall they are conveyed initially to the liver and lungs and eventually to other tissues. The syndrome is described in The Lancet4 as being characterized by persistent eosinophilia, hepatomegaly, fever and asthmatic attacks, bronchitis, or other evidence of pulmonary involvement, and is often associated with anaemia, leucocytosis, and raised gamma-globulin levels. Human infection has been reported&dquo;«7 8 9 1011 12 13 14 16. Usually the condition is relatively benign, but fatalities have been reported17 18 and in these instances Toxocara canis larvae have been demonstrated in brain tissue at necropsy. Eye involvement is specifically mentioned by most authors’ ’4. Woodruff2 posed the question of how common the infection is in dogs and cats in Britain, and commented on the fact that very little information could be found. In 1927 Lewis’9 found 16.3 per cent of 43 dogs and 61.8 per cent of 155 cats in Aberystwyth to be infected. Hutchinson 21 in Glasgow records a 13.7 per cent infection in 1707 cats. Woodruff et al2’ reported the first of a series of examinations of faecal specimens from homes for dogs and cats in the Home Counties and over an eight year period 1,107 samples yielded an overall prevalence rate of 12.8 per cent2. Oldham2z in London ,found Toxocara canis in 6.4 per cent of 250 dogs and 15
Toxocara cati in 8 per cent of 100 cats at necropsy. Dubey23 also in London demonstrated a 35.4 per cent infection rate in 110 cats at necropsy, and Niak 24 in necropsies in Liverpool showed a 39.7 per cent infection rate in 71 cats. Weston25 examined faeces from 555 cats supplied for laboratory use from ten sources. The incidence of Toxocara cati infestation ranged from 45 per cent in untreated source cats to 9.6 per cent in the best suppliers cats. CURRENT STUDY THIS PAPER reports results of 2,013 canine faecal examinations (Table I) and 202 feline faecal examinations (Table II) over a two year period. Faecal samples are sent by veterinary surgeons and practitioners throughout the United Kingdom to Mansi Laboratories for examination. In the majority of cases the examination is requested because of intestinal disturbance. Histories, where given, include comments such as &dquo;purchased from dealer, chronic diarrhoea for several weeks&dquo;, &dquo;thin, occasional diarrhoea&dquo;, &dquo;losing weight though eating well&dquo; and &dquo;periodic blood stained diarrhoea contacts: children&dquo;. -
Toxocara canis ova were found in 52 (2.58 per cent) of 2,013 canine faecal samples, and Toxocara cati ova in 8 (3.96 per cent) of 202 feline faecal samples. In the 52 positive Toxocara canis animals, the ages were stated in 25 cases. These ranged from 10 weeks to 5 years. Fourteen were 6 months of age or less. The results in this study show a much lower incidence of infection than earlier published work. A possible explanation might be that owners of the animals involved were sufficiently interested in the welfare of their pets to seek advice and treatment from a veterinary surgeon, and it could be supposed that the general level of health of their pets was above average. It is also of interest to note that Woodruff2 observed that in recent years there has been a tendency for the prevalence rate to fall, and he believes that this is related to worming carried out because of the publicity his work has had. This is illustrated by the fact that in 1964 he obtained a 21.7 per cent rate of isolation of Toxocara canis ova from canine faecal samples, and by 1969 the isolation rate had progressively fallen to 2.5 per cent. The Lancet4 points to puppies as being the main source of infection, and Woodruff et apt consider young animals as probably the main reservoir of infection, with the greatest risk of acquiring the disease probably into a occurring when an infected puppy is household in which there are children. Mansiconfirms the danger from young puppies and has observed that
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brought
280 TABLEI
EXAMINATION OF 2013 CANINE FAECAL SAMPLES POSITIVE SPECIMENS PARASITE
NUMBER POSITIVE
% OF TOTAL EXAMINED
52 65 19 6 4 2 2 2 3
2.58 3.23 0.94 0.33 0.2 0.1I 0.1I 0.1I 0.155
Toxocara Canis Toxascaris Leonina Ancylostoma Caninum Trichuris Vulpis Uncinaria Stenocephala
Dipylidium Caninum Filaroides Osleri Giardia Coccidia
TABLE II EXAMINATION OF 202 FELINE FAECAL SAMPLES - POSITIVE SPECIMENS PARASITE
NUMBER POSITIVE
Toxocara Cati Toxascaris Leonina Toxocara Mystax Taenia Taeniaeformis
8 4 2 1 1 1
Capillaria Aerophila
Coccidia
% OF TOTAL EXAMINED
3.96 1.98 0.99 0.49 0.49 0.49
whilst older animals carry adult worms, the ova passed by them are frequently distorted in shape and appear to be less viable. THE RESPONSIBILITIES OF PET OWNERSHIP In 1973, Jordan26 estimated the pet population of the United Kingdom to include 5.2 million dogs and 3.7 million cats. Sheridan2’ refers to the benefits of pet ownership and points to the fact that in addition to the pleasure of companionship, often real psychological needs are met. Dogs also undertake many other useful functions ranging the blind, to use in crime prevention and detection, and the arrest of felons. Nevertheless it has been clearly established that there is a significant number of dogs and cats excreting Toxocara ova, and although the level of animal infection, as observed by Woodruff2 and reported here, appears to have fallen, the hazard to human health is considerable. A realistic and responsible approach could greatly reduce this problem.
from guiding
CONTROL OF TOXOCARIASIS 1. Detection
of Infection
in Man
Woodruff2 29 deals at length with immunological methods in the form of a skin test and a fluorescent antibody test. His work has shown that about 2 per cent of the apparently healthy population has been infected with this worm. As a result of his diagnostic methods, many eyes that might have been removed on the
assumption
that
a
malignant
tumour is
present, have
been saved because of confirmation of toxocaral
enophthalmitis.29 2. Infection in Animals It would be far simpler if presentation of symptoms in animals was an indication of infection, but Churcher3° in his study of 24 infected dogs found that only 3 were showing symptoms. He recommends that all adult dogs should have six monthly faecal examinations for the presence of intestinal worms, and that the result of each alternative examination could be used when obtaining a new dog licence. The evidence suggests that puppies should be dewormed before sale, and that subsequent deworming should be carried out frequently during the ,
first six months of life, and from then on, as and when evidence of worms is found. 3. Infection in the Environment In his report to the Environmental Health Committee of Runnymede District Council, Fabel3’referred to the fact that in London alone estimated faeces deposited daily on pavements and parks is 66 tons. In the absence of legislation the onus must fall on dog owners to train their dogs to defaecate in areas where the faecal matter can be buried or suitably destroyed. In any event, the defaecation in areas where children play should be avoided by segregation. This can only be effectively achieved by the enforcement of suitable bye-laws. One of the London Boroughs has undertaken to provide exercise areas exclusively for dogs. Sandpits in recreational areas are particularly hazardous, and Fabep2 recommends treatment with bleaching powder or Chloros, with subsequent application of water to neutralize the disinfecting agent. Bisseru33 mentions that the ova are susceptible to direct sunlight, although when deposited the ova are usually protected by surrounding faecal debris. 4. Health Education Area Health Authorities have now well established Health Education departments, and prevention of disease is one of their major objectives. Schoolchildren present the most susceptible sector of the public in health education, and a programme aimed at them would have considerable effect. Environment Health Officers and District Community Physicians could all contribute to this work. Companies marketing pet foods could also play a useful part in this campaign by incorporating with their advertising labels, leaflets and posters, suitable reminders of the need to observe hygiene rules with pets. The Health Education Council and other organizations could lend their support. ACKNOWLEDGEMENT The author records his appreciation of the encouragement and helpful criticism received from Dr. W. Mansi, Director, Mansi z
Laboratories, Weybridge. REFERENCES
1 HODGMAN. S. F. J. (1967) Domestic Pets and their Relationship to Human Disease, Royal Society of Health Journal, 87, 2, 116. 2 WOODRUFF, A. W. (1970) Toxocariasis The Watson Smith lecture, British Medical Journal, 3, 664. 3 BROWN. D. H. (1970) Ocular Toxocara Canis, Part II, Clinical Review, Journal of Paediatric Ophthalmology, 7, 182. EDITORIAL (1972) Toxocara, The Lancet, 1, 730. 4 5 WILDER. H. Ç. (1950) Nematode Endophthalmitis, Transactions of the American Academy of Ophthalmology and Otolaryngology, —
55, 99. 6 BEAVER, P. C., SNYDER. C. M., CARRERA. G. M., DENT. J. M. and LAFFERTY. J. W. (1952), Chronic Eosinophilia due to Visceral
Larva Migrans, Report of Three Cases, Pediatrics, 9, 7. 7 NICHOLS. R. L. (1956), The Etiology of Visceral Larva Migrans, Journal of Parasitology, 42, 349. 8 ASHTON, N. (1960), Larval Granulomatosis of the Retina Due to Toxocara, British Journal of Ophthalmology, 44, 129. 9 WOODRUFF. A. W., ASHTON. N., and STOTT. G. J. (1961), Toxocara Canis Infection of the Eye, Transactions of the Royal Society of Tropical Medicine and Hygiene, 55, 13. 10 DUGUID. I. M. (1961), Chronic Endophthalmitis Due to Toxocara, British Journal of 45, 705. 11 BIRD. A. C., SMITH. J. L., and CURTIN. V. T. (1970), Nematode Optic Neuritis, American Journal of Ophthalmology, 69, 72. 12 PHILLIPS. C. I., and MACKENZIE, A. D. (1973), Toxocara Larval Papillitis, British Medical Journal, 1, 154. 13 RAISTRICK, E. R., and DEAN HART, J. C. (1975), Adult Toxocaral Infection with Focal Retinal Lesion, Brit. Med. J., 3, 416. 14 PERKINS. E. S. (1966), Pattern of Uveitis in Children, British Journal of Ophthalmology, 50, 169. 15 KUZEMO. J. A. (1966), Toxocariasis in Sibs, Archives of Diseases of Children, 41, 221. 16 DICKSON, W., and WOODCOCK. R. C. (1959), Visceral Larva Migrans, Archives of Diseases of Children, 34, 63.
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Ophthalmology,