Woodstock, Ontario. Brossard, Quebec. Howick, Quebec. Hudson, Quebec. Kirkland, Quebec. L'Assomption, Quebec. Laval, Quebec. Montreal, Quebec.
Heartworm in Dogs in Canada in 1985 J. OWEN D. SLOCOMBE AND IAN McMILLAN
Department of Pathology, Ontario Veterinary College (Slocombe) and Department of Animal and Poultry Science, Ontario Agricultural College (McMillan), University of Guelph, Guelph, Ontario NI G 2 WI
ABSTRACT
In late December 1985, 1485 institutional veterinarians and small and mixed animal clinics across Canada were sent a questionnaire in order to assess the status of Dirofilaria immitis in Canada in 1985 and 44% of them responded. Veterinarians reported that 137,300 dogs were blood-tested to check for microfilariae and 1210 dogs were found with heartworm. Another 36 dogs were amicrofilaremic but diagnosed with heartworm disease to give the total number diagnosed in 1985 as 1247 (0.91 %). Heartworm was reported from all provinces except Prince Edward Island, Newfoundland and Saskatchewan but most (1126) of the cases were in Ontario. Southwestern Ontario continued to be the primary focus of the infection in Canada. From Quebec, 91 cases were reported mostly from and around Montreal. From Manitoba, 19 cases were reported from Winnipeg and surrounding areas. Heartworm was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. About 28% of the cases were observed with clinical signs of heartworm disease and 78% had a history of not having left Canada.
Key words: Dirofilaria immitis, heartworm, dogs, prevalence, Canada. RtSUM t
Dirofilariose canine au Canada en 1985 Vers la fin de decembre 1985, les auteurs adresserent un questionnaire a 1485 veterinaires des diverses provinces du Canada qui oeuvrent dans des
tional veterinarians and small and mixed animal clinics throughout Canada to assess heartworm disease (HWD) primarily in dogs, in 1985 as was done previously (1-9). The number returned was 656 (44% response). A few additional questionnaires were returned because of inappropriate addresses. The findings are presented in two figures and three tables and a few brief comments about these should be made. 1. The percentage response for 1985 was higher than 1984 (35% response) and this occurred because we were able to be more selective in sending out the questionnaires. Hopefully, all clinics attending to dogs and cats received a questionnaire. Of those clinics that responded, 89% indicated an interest in information on HWD and 96% stated that they would complete a questionnaire if offered again. 2. In 1985, 39,506 more dogs were checked for microfilariae than in 1984. The increase in testing was primarily in Quebec and Ontario. Eight practices reported that they used the smear as the only blood test procedure. We have commented previously that this procedure is very inefficient for recovering microfilariae. We encourage practices to use a concentration technique as part of the laboratory examination. 3. In 1985, 1247 dogs (0.91% of dogs tested) were found with HWD compared with 1451 (1.48%) in 1984. There were 36 amicrofilaremic dogs Mots cles : Dirofilaria immitis, dirofi- that were diagnosed with HWD. Heartworm disease was diagnosed in lariose, prevalence, Canada. all provinces except Prince Edward Island, Newfoundland and SaskatcheIn late December 1985, 1485 wan but as seen previously, nearly all questionnaires were sent to institu- of the cases were in Ontario. Heart-
laboratoires, des cliniques de petits animaux ou des pratiques mixtes. Ils voulaient ainsi connaitre la situation de la dirofilariose au pays, pour l'annee 1985; 44% des veterinaires vises repondirent au questionnaire. Le releve demontra que 137,300 chiens avaient subi l'epreuve sanguine destinee deceler la dirofilariose et que 1210 etaient parasites par Dirofilaria immitis. On considera aussi 36 autres chiens comme atteints de la maladie, meme si leur sang ne recelait pas de microfilaires. Ceci donna un resultat global de 1247 cas de dirofilariose, impliquant 0,91% des chiens eprouves dans le cadre du releve. La maladie sevit dans toutes les provinces, a l'exception de l'Ile-duPrince-Edouard, de Terre-Neuve et de la Saskatchewan. La plupart des cas, c'est-a-dire 1126, provenaient de l'Ontario et le sud-ouest de cette province represente toujours le principal foyer d'infection. Les 91 cas diagnostiques au Quebec interessaient surtout Montreal et ses environs. Quant aux 19 cas diagnostiques au Manitoba, ils survinrent a Winnipeg et ses environs. La maladie affectait principalement des chiens ages de plus de trois ans et vivant surtout a l'exterieur, dans les campagnes. Environ 28% des chiens parasites manifestaient les signes cliniques de la maladie et l'anamnese de 78% des chiens atteints de dirofilariose revela qu'ils n'avaient jamais quitte le Canada.
Supported by Norden Laboratories Inc., Lincoln, Nebraska.
324
Can Vet J 1986; 27: 324-328.
) FALLS
FIGURE 1. Areas in Canada with diagnoses of heartworm disease in dogs in 1985. * Areas with dogs which had been outside of Canada and presumed infected before returning with dogs whose movements were unknown + Areas with dogs some of which had never left Canada
or
+
+
+~~~~~~~~
0
ACTON AMHERSTBURG CHATHAM ESSEX GLOUCESTER HUNTSVILLE INGERSOLL KINCARDINE KING CITY MOUNT BRYDGES OTTAWA OWEN SOUND PORT ELGIN STITTSVILLE WESTON
AYLMER BARRIE BEAVERTON BRANTFORD BRAMPTON BURLINGTON CALEDONIA CAMBRIDGE CAMPBELLVILLE CHARING CROSS DRESDEN DUNNVILLE FOREST FORT ERIE GEORGETOWN GLENCOE GRASSIE
GRIMSBY GUELPH HAGERSVILLE HAMILTON INGLEWOOD KESWICK KINGSVILLE LAMBETH LEAMINGTON LONDON MAPLE MISSISSAUGA MOUNT HOPE MOUNT ALBERT NEW DUNDEE NEWMARKET NIAGARA NORWICH OAKVILLE OLDCASTLE PETERBOROUGH PORT COLBORNE
PORT DOVER QUEENSVILLE REXDALE ST. THOMAS SARNIA SIMCOE SMITHVILLE STIRLING STRATHROY THOROLD TILLSONBURG TORONTO WALKERTON WALLACEBURG WATERDOWN WATFORD WELLAND WESTHILL WHEATLEY WILLOWDALE WINDSOR WOODSTOCK
FIGURE 2. Areas in Ontario with diagnoses of heartworm disease in dogs in 1985. * Areas with dogs which had been outside of Canada and presumed infected before returning or with dogs whose movements were unknown + Areas with dogs some of which had never left Ontario
worm disease was found most frequently in companion dogs over three years of age maintained mainly outdoors in rural areas. Clinical signs of HWD were observed in 28% of the cases. 4. The percentage of dogs with HWD with a history of not having left Canada was about 78%. This was similar to that for previous years except in 1982 when it was 43%. For about 16% of dogs with HWD the movement in and out of the province or Canada was unknown. Southwestern Ontario continued to be the focus of the infection in Canada. Other foci of infection appeared to lie in and around Montreal, Quebec where there were 91 dogs reported with HWD and in and around Winnipeg, Manitoba where there were 19 cases. There was one case reported from Devon, Alberta that had been in Quebec, and two in Grand Falls, Newfoundland that had been in another province in Canada. 5. In Ontario, the number of dogs with HWD in 1985 was 1126 (1310 in 1984). There were 115 clinics (118 in 1984) and 76 towns (81 in 1984) reporting a diagnosis of HWD in 1985. In Amherstburg, Charing Cross, Chatham, Essex, Kingsville, Leamington, Oldcastle, Wheatley and Windsor there were 444 cases (609 in 1984). There were 15,088 dogs tested (14,648 in 1984) to give a prevalence of 2.94% (4.2% in 1984). In Dresden, Forest, Glencoe, Petrolia, Sarnia, Strathroy, Wallaceburg and Watford there were 65 cases (82 in 1984). There were 5296 dogs tested (3445 in 1984) to give a prevalence of 1.23% (2.38% in 1984). Along Lake Erie and including Aylmer, Caledonia, Dunnville, Fonthill, Fort Erie, Fisherville, Hagersville, Mount Hope, Niagara Falls, Port Colborne, Port Dover, Simoce, Smithville, St. Thomas, Thorold, Tillsonburg and Welland there were 425 cases (337 in that general area in 1984). As in previous years most of the cases were in Simcoe and Tillsonburg. There were 14,936 dogs tested (11,967 in that general area in 1984) to give a prevalence of 2.85% (2.8 1% in 1984). In London and the surrounding areas of Huron Park, Ingersoll, Kirkton, Lambeth, Mount Brydges, Stratford, Tavistock and Woodstock 325
TABLE I RESULTS OF A QUFSTIONNAIRE WHICH WAS SENT TO 1485 VETERINARIANS OR CLINICS IN CANADA IN DECEMBER 1985 AND COMPUTED FROM 656 REPLIES
Heartworm in Canada 1985 V Name-
Address:
1. Does your professional activity include examination of dogs, cats? If YES go to Question 2. If NO go to question 24 2. Which category would fit your activity best? Mixed 215 Small animal practice 407 Research I Diagnostic 4 Other 0 3. What technique(s) do you use for diagnosis of HWD? % Clinical Signs 46 Radiography 29 Blood test 93 Necropsy 18 4. If blood tests, specify techinique(s) used routinely % Knotts 29 Filter 51 Smear 16 Microcapillary 6, Submitted to a diagnostic lab 27 Immunodiagnosis Dirotect 3 5. If blood is routinely submitted to a lab for diagnosis, is this for: Microfldariae ID 60%, Immunodiagnosis 18% 6. What time of year do you test (blood) most dogs for HWD? % Spring 53 Summer 32 Fall 9 Winter 6 7. No. of dogs blood tested in 1985 8. No. of dogs diagnosed with HWD in 1985 and microfilaremic 9. No. of dogs diagnosed with HWD in 1985 and amicrofilaremic 10. Total no. of dogs diagnosed with HWD in 1985 11. No. of dogs diagnosed with HWD in 1985 and with clinical signs of HWD 12. Circle month(s) you diagnosed most heartworm cases in 1985 % Dec Nov Oct June Mar Sept Feb July Aug Jan Apr May 4 4 1 1 14 22 15 10 5 0 23 13. How many cases of HWD had the following histories in 1985? Six months or more prior to diagnosis was outside of Canada Six months or more prior to diagnosis was in another province Never left the province Movement unknown 14. For dog(s) with HWD that never left Ontario identify No. of cases that never left your area No. of cases that in the summer visited endemic areas in Ontario (e.g. Windsor, Lake Erie, etc.) Unkown For Questions 15 through 18 give the number (or percentage of those dogs with HWD in 1985 according to the following classifications. (The numbers were converted to frequencies where most frequent = 1) 4 Unknown I Rural Suburb 3 15. Domicle of dogs City -2 Unknown - 3 Primarily outdoors I 16. Location in domicile Primarily indoors 2 1-3 years- 2 Less than I year 4 17. Age of dogs Greater than 3 years I Age unknown 3 Hunting dog- 3 18. Principle activity of dogs Companion dog I Show dog -5 Unknown- 4 Farm dog -2 19. Do you recommend a preventive program for your area? 20. No, of cases diagnosed with Dipetalonema reconditum in 1985? 21. No. of cases of D. immitis in cats diagnosed in 1985? 22. No. of cases of D. immitis in other animals 23. For which of the above questions (Q) was the information supplied based on your medical records (expressed as a % of respondents to those questions): Q13 Q12 QIO QIJ Q9 Q8 Q7 Q6 60 69 72 47 51 54 58 53 Q22 Q20 Q21 Q18 Q17 Q16 Q15 Q14
YES 626
NO 30
-
-
137,300 1,209 37 1,247
345 (28%)
71 (5.7%) 10 (0.8%) 960(77.0%) 206( 16.5%)
767(87.5%) 41 (4.7%) 69 (7.9%)
-
-
-
-
-
-
-
-
24. 25. 26. 27. 28. 29. 30.
59 62 58 62 62 Would you be interested in the results of this questionnaire? % Would you be interested in information on HWD? % Would news releases on HWD be helpful to the public? % Did you respond to the 1984 Heartworm questionnaire? % Did you see the results of the 1984 questionnaire? % Would you respond to the questionnaire if it was offered again? % Any other comments: 133 respondents made comments.
326
41
42
YES 329 (53%)
49 4 0
42
YES 97 YES 89 YES 87 YES 76 YES 73 YES 96
NO
2
No
8
NO
8
NO
17
NO 22 NO
2
TABLE II AREAS IN CANADA WITH Two OR MORE DOGS DIAGNOSED WITH HEARTWORM DISEASE IN 1985
Area
Richmond, British Columbia Selkirk, Manitoba Steinbach, Manitoba Winnipeg, Manitoba Amherstburg, Ontario Aylmer, Ontario Barrie, Ontario Brantford, Ontario Burlington, Ontario Caledonia, Ontario Cambridge, Ontario Charing Cross, Ontario Chatham, Ontario Dunnville, Ontario Essex, Ontario Fort Erie, Ontario Georgetown, Ontario Glencoe, Ontario Grassie, Ontario Guelph, Ontario Hagersville, Ontario Hamilton, Ontario Keswick, Ontario Kincardine, Ontario Kingsville, Ontario Lambeth, Ontario Leamington, Ontario London, Ontario Mississauga, Ontario Mount Brydges, Ontario Newmarket, Ontario Niagara Falls, Ontario Norwich, Ontario Oakville, Ontario Oldcastle, Ontario Ottawa, Ontario Peterborough, Ontario Port Colborne, Ontario Port Dover, Ontario Queensville, Ontario Rexdale, Ontario Sarnia, Ontario Simcoe, Ontario St. Thomas, Ontario Stittsville, Ontario Strathroy, Ontario Tillsonburg, Ontario Toronto, Ontario Walkerton, Ontario Wallaceburg, Ontario Watford, Ontario Welland, Ontario Weston, Ontario Wheatley, Ontario Willowdale, Ontario Windsor, Ontario Woodstock, Ontario Brossard, Quebec Howick, Quebec Hudson, Quebec Kirkland, Quebec L'Assomption, Quebec Laval, Quebec Montreal, Quebec Pointe Claire, Quebec St-Eustache, Quebec Ste-Julienne, Quebec St-Lambert, Quebec St-Louis-de-Terrebonne, Quebec Ste-Therese, Quebec Kentville, Nova Scotia Grand Falls, Newfoundland
Number of Cases Never Had Been Outside Canada or Left Movement Unknown Canada 2 7 0 1 15 13 0 6 2 0 0 0 11 0 50 I
0 2 2 5 0 5 3
62 14 2 11 55 15 0 3 2 9 2
0 0 I 4 0 2 0 2 0 0 0 2 3 8 I I
5 8 2 0 21 5 35 4 I 0 7 2
4 l
4 7
0 3 0 0 0 0 I l 0 0 2 0 2 3 l 0 2 11 2 4 0 81 0 0 3 2 0 0 1 2
65 0 13 14 7 2
0
13 101 5 0 2 207 l
28 8 8 0
10 2 86 3 2 2 24 2 4
10 4 2
0
l
2 0
5 17 0 2
there were 23 cases (25 in that general area in 1984). There were 10,507 dogs tested (8867 in that general area in 1984) to give a prevalence of 0.22% (0.28% in 1984). The number of cases reported from Brantford, Cambridge, Elmira, Elora, Fergus, Guelph, Kitchener, New Dundee, New Hamburg and Waterloo was 76 (119 in 1984). There were 10,451 dogs tested (9995 in 1984) to give a prevalence of 0.73% (1.19% in 1984). In Ancaster, Burlington, Dundas, Grassie, Grimsby, Hamilton, St. Catharines, Waterdown and West Flamborough there were 18 cases (6 in 1984). There were 9333 dogs tested in that general area (9123 in 1984) to give a prevalence of 0.19% (0.07% in 1984). In Acton, Bramalea, Brampton, Campbellville, Carlisle, Georgetown, Inglewood, Malton, Mississauga, Norval, Oakville and Orangeville there were 18 cases (27 in 1984). There were 9896 dogs tested (8109 in 1984), to give a prevalence of 0.18% (0.33% in 1984). In Metropolitan Toronto including
Agincourt, Downsview, Etobicoke, Rexdale, Scarborough, Westhill, Weston and Willowdale there were 11 cases (14 in 1984). There were 13,655 dogs tested (8479 in 1984) to give a prevalence of 0.08% (0.16% in 1984). In the area between Metropolitan Toronto and Lake Simcoe and up to Beaverton on the east and Barrie on the west there were 18 cases (56 in 1984). In that area there were reports also from Aurora, Keswick, King City, Maple, Markham, Mount Albert, Newmarket, Nobelton, Queensville, Richmond Hill, Schomberg, Stouffville, Thornhill, Tottenham, Unionville, Uxbridge and Woodbridge. There were 9528 dogs tested (6745 in that general area in 1984) to give a prevalence of 0.19% (0.83% in 1984). In Atwood, Blyth, Chesley, Exeter, Goderich, Kincardine, Markdale, Mildmay, Port Elgin, Ripley, Seaforth, Walkerton and Zurich areas there were five cases (7 in 1984). There were 801 dogs tested (651 in 1984) to give a prevalence of 0.62% (1.08% in 1984). 6. There were 48 cases of Dipetalonema reconditum reported in 1985 (37 in 1984). Most of the,cases (40) were in 327
I
TABLE III
NUMBER OF CLINICS OR LABORATORIES REPORTING THAT THEY HAD BLOOD TESTED (BT) DOGS AND THE NUMBER OF DOGS DIAGNOSED WITH HEARTWORM DISEASE (HWD) IN 1985 IN THE PROVINCES
British Columbia Alberta Saskatchewan Manitoba Ontario Quebec Nova Scotia New Brunswick Prince Edward Island Newfoundland Total
Ontario. There were four cases of HWD in cats, three in Quebec and one in Ontario. 7. This report identifies a decrease in the number of cases and prevalence of HWD in Canada in 1985 over 1984. The decrease was probably due to two factors. First, in 1984 a survey was conducted near Brantford, Ontario on a reserve where a large number of cases were found and this survey was not repeated in 1985. Secondly, there was a decline in reporting from clinics in Ontario normally finding a large number of cases. We believe that continued surveillance for HWD is needed. 8. We have attempted in this report to provide you with information which would be useful for discussion and making decisions with your clients on whether to blood test for HWD or not and whether to use preventive medication or not. We cannot define a precise
328
No. of Clinics 37 33 15 23 316 75 12 7 5 4 527
No. of Dogs BT HWD 212 4 3 176 95 0 19 3,976
122,622 9,645 220 268 47 39 137,300
1,126 91 2 0 0 2 1,247
level of infection at which it becomes necessary to blood test all dogs or to put all dogs on a preventive program. However, in order to gain the best estimate of the prevalance of HWD, we encourage blood testing. This is especially important in Ontario for practices south of a line drawn from the southern end of Lake Simcoe to Grand Bend, in Quebec around Montreal and in Manitoba around Winnipeg. We encourage blood testing once a year in the spring and not earlier than mid-April and preferably in May for all dogs regardless of whether they were given preventive medication previously. We encourage the use of preventive medication in areas where it seems most important. One area is in southwestern Ontario in the region of Forest-Sarnia-Chatham-Windsor, along the Lake Erie shoreline and in the triangular area bounded by
Niagara Falls, Brantford and Aylmer. It would appear also that preventive medication may be useful in Ontario in the area between Toronto and Lake Simcoe and in the area bounded by the western end of Lake Ontario to the east and the Niagara escarpment to the west. Other areas in Canada where preventive medication appears useful are Quebec, in and around Montreal and Manitoba in and around Winnipeg. We also encourage the use of preventive medication for all dogs entering those defined areas from June through September. REFER ENCES 1. SLOCOMBE, JOD. Heartworm in dogs in Canada in 1977. Can Vet J 1978; 19: 244-247. 2. SLOCOMBE JOD, McMILLAN i. The geographic distribution of heartworm in Canada. In: Morgan HC et al, eds. Proceedings of the Heartworm Symposium - 1977. Bonner Springs, Kansas: VM Publishing Inc., 1978: 5-7. 3. SLOCOMBE JOD, McMILLAN i. Heartworm in
dogs in Canada in 1978. Can Vet J 1979; 20: 284-287. 4. SLOCOMBE JOD, McMILLAN 1. Heartworm in dogs in Canada in 1979. Can Vet J 1980; 21:
159-161. 5. SLOCOMBE JOD, McMILLAN i. Heartworm in dogs in Canada in 1980. Can Vet J 1981; 22:
201-203. 6. SLOCOMBE JOD, McMILLAN i. Heartworm in
dogs in Canada in 1981. Can Vet J 1982; 23: 219-221. 7. SLOCOMBE JOD, McMILLAN i. Heartworm in dogs in Canada in 1982. Can Vet J 1983; 24:
227-229. 8. SLOCOMBE JOD, McMILLAN 1. Heartworm in dogs in Canada in 1983. Can Vet J 1984; 25:
347-350. 9. SLOCOMBE JOD, McMILLAN i. Heartworm in
dogs in Canada in 1984. Can Vet J 1985; 26: 323-327.
