Demographics and questionnaire
Samples were collected from 3,022 dogs in 288 dog parks during July and August 2019. Sixteen samples were disqualified because they were not accompanied by completed questionnaires or because insufficient feces were available for testing. Thus, fecal testing results and questionnaires were available from 3,006 dogs. The most commonly represented age group was young adult (1 to 3 years) (n = 1,371, 45.6% of 3,006 dogs), followed by senior (≥ 7 years) (659, 21.9%), mature adult (4 - 6 years) (613, 20.4%) and puppy (< 12 months) (363, 12.1%). Within the puppy group, 72 dogs (2.4%) were less than 6 months of age. Of the 3,006 dogs, 1,317 (43.8%) were female, of which 1,183 (89.8%) had been spayed while 1,689 (56.2%) were male, of which 84.6% had been neutered. As reported by owners, the most commonly represented breeds were: Labrador Retriever (356, 11.8% of sampled dogs), German Shepherd Dog (187, 6.2%), Golden Retriever (137, 4.6%), Australian Shepherd (103, 3.4%), Siberian Husky (102, 3.4%), Chihuahua (83, 2.8%), and Boxer (64, 2.1%). The breeds of 547 dogs (18.2%) were described as mixed or were not specified.
In response to the question on nematode parasite control, 2,069 owners (68.8%) stated that they were currently providing a HWCM for their dog. Of those owners, 1,847 (89.3%) reported using an oral formulation, 68 (3.3%) a topical formulation, and 144 (7.0%) an injection. Ten owners did not know how the HWCM was being administered (Table 2). The proportion of dogs reported to be currently receiving a HWCM was significantly higher (P < 0.0001) in those previously infected with intestinal parasites (79.2%) (estimated difference of proportions 0.111; 95% CI, 0.075, 1), compared with those without known prior intestinal worm infection (68.1%). Regionally, owner-reported HWCM use in the West was significantly lower than in each other region (P < 0.0001). No other between-region differences were significant. By dog age grouping, the frequency of use of a HWCM was similar at approximately 70% for puppies through mature adult dogs, while 63.6% of owners of senior dogs reported that they were providing a HWCM.
Table 2. Number of owners (%) reporting currently using a heartworm/intestinal parasite control medication, by region and formulation
Medication use
|
Southeast
(n = 989)
|
Northeast
(n = 400)
|
Midwest
(n = 708)
|
West
(n = 909)
|
National
(n = 3006)
|
Yes
|
829 (83.8)
|
317 (79.3)
|
570 (80.5)
|
353 (38.8)
|
2069 (68.8)
|
95% CI
|
81.5, 86.1
|
75.3, 83.2
|
77.6, 83.4
|
35.7, 42.0
|
67.2, 70.5
|
No
|
14 (14.8)
|
68 (17.0)
|
135 (19.1)
|
536 (59.0)
|
885 (29.4)
|
95% CI
|
12.6, 17.0
|
13.3, 20.7
|
16.2, 22.0
|
55.8, 62.2
|
27.8, 31.1
|
Unknown
|
14 (1.4)
|
15 (3.8)
|
3 (0.4)
|
20 (2.2)
|
52 (1.7)
|
95% CI
|
0.7, 2.2
|
1.9, 5.6
|
0.1, 0.9
|
1.3, 3.2
|
1.3, 2.2
|
Formulation (n, % of dogs on heartworm/intestinal control medication)
|
Oral
|
728 (87.8)
|
299 (94.3)
|
497 (87.2)
|
323 (91.5)
|
1847 (89.3)
|
95% CI
|
85.6, 90.0
|
91.8, 96.9
|
84.5, 89.9
|
88.6, 94.4
|
87.9, 90.6
|
Topical
|
23 (2.8)
|
8 (2.5)
|
27 (4.7)
|
10 (2.8)
|
68 (3.3)
|
95% CI
|
1.7, 3.9
|
0.8, 4.3
|
3.0, 6.5
|
1.1, 4.6
|
2.5, 4.1
|
Injectable
|
74 (8.9)
|
9 (2.8)
|
43 (7.5)
|
18 (5.1)
|
144 (7.0)
|
95% CI
|
7.0, 10.9
|
1.0, 4.7
|
5.4, 9.7
|
2.8, 7.4
|
5.9, 8.1
|
CI – confidence interval
Fecal test results
Using CAI and CF, intestinal parasites were detected in 622 (20.7%) samples, with 8.8% positive for one or more of the following nematodes: hookworm, whipworm, ascarids (Table 3). Of the 288 parks, 245 (85.1%) provided samples positive for any intestinal parasites, with 49.7% positive for at least one of the aforementioned nematodes. The most commonly detected parasite was Giardia, while hookworm was the most commonly detected nematode. Other canine parasites detected on CF included Cystoisospora spp. (n=16 dogs), Alaria sp. (n=1), capillarids (n=2), Spirometra sp. (n=2), and a taeniid egg (n=1). The spurious parasite Eimeria spp. were identified in samples from 37 (1.2%) of dogs.
Table 3. Number (%; 95% confidence interval) of dogs and parks with ≥1 sample positive for intestinal parasites by coproantigen immunoassay or centrifugal flotation
|
Dogs
|
Dog Parks
|
|
Number (%; 95% CI)
(N = 3006)
|
Number (%; 95% CI) (N = 288)
|
Any parasitic species‡
|
622 (20.7; 19.3, 22.2)
|
245 (85.1; 80.5, 88.8)
|
Nematodes# and/or Giardia
|
609 (20.3; 18.9, 21.7)
|
243 (84.4; 79.7, 88.1)
|
Giardia spp.
|
391 (13.0; 11.9, 14.3)
|
213 (74.0; 68.6, 78.7)
|
Nematodes#
|
263 (8.8; 7.8, 9.8)
|
143 (49.7; 49.7, 55.4)
|
Hookworm
|
214 (7.1; 6.3, 8.1)
|
125 (43.4; 37.8, 49.2)
|
Whipworm
|
58 (1.9; 1.0, 1.8)
|
52 (18.1; 14.0, 22.9)
|
Eimeria spp.
|
37 (1.2; 0.9, 1.7)
|
33 (11.5; 8.2, 15.7)
|
Ascarid
|
17 (0.6; 0.3, 0.8)
|
16 (5.6; 3.4, 8.9)
|
Cystoisospora
|
16 (0.5; 0.3, 0.9 )
|
16 (5.6; 3.4, 8.9)
|
Alaria
|
1 (0.0; 0.0, 0.2)
|
1 (0.4; 0.0; 2.1)
|
Capillarids
|
2 (0.1; 0, 0.3)
|
1 (0.4; 0.0, 2.1)
|
Spirometra
|
2 (0.1; 0, 0.3)
|
2 (0.7; 0.0, 2.7)
|
Taeniid
|
1 (0.0; 0.0, 0.2)
|
1 (0.4; 0.0, 2.1)
|
‡Includes all parasitic species of nematodes, as well as Alaria, Cystoisospora, and Spirometra and taeniid.
#Nematodes: hookworm, whipworm, ascarid (includes coinfections)
Use of CF and microscopy allowed identification of hookworm and ascarid ova. Of 110 samples positive for hookworm ova, 108 (98.2%) were Ancylostoma caninum, 2 (1.8%) were Uncinaria stenocephala. Of 12 samples positive by CF for ascarids, 11 (91.7%) were Toxocara canis and 1 (8.3%) was Toxascaris leonina. Of the 42 ova with bipolar plugs, two were Eucoleus aerophilus, the remainder were T. vulpis.
A 4-sample test for equality of proportions of age groups with positive tests for one or more of hookworm, whipworm and ascarids was significant (P < 0.0001), with the highest prevalence in dogs less than 12 months of age. Infection with hookworm, whipworm and Giardia was detected regardless of age group, while ascarid infection was only identified in samples from dogs under 4 years of age (Figs 1 and 2; Table 4). Dogs reported to be currently on a HWCM had a significantly lower proportion of positive test results for hookworm, whipworm or ascarid (7.5%) than those not receiving a HWCM (11.4%) (P = 0.0003; estimated difference of proportions -0.039; 95% CI, -1, -0.018) (Table 5).
Table 4: Number (%) of dogs positive for intestinal parasites by coproantigen immunoassay or centrifugal flotation by age grouping
Demographic category
|
Nematodes/ Giardia
|
Nematodes
|
Hookworm
|
Whipworm
|
Ascarid
|
Giardia
|
< 12 months; puppy (n = 363)
|
152 (41.9)
|
50 (13.8)
|
35 (9.6)
|
14 (3.9)
|
11 (3.0)
|
121 (33.3)
|
95% confidence interval
|
36.9, 47.0
|
10.6, 17.7
|
7.0, 13.1
|
2.3, 6.4
|
1.6, 5.4
|
28.7, 38.3
|
1 – 3 years; young adult (n = 1371)
|
307 (22.4)
|
132 (9.6)
|
108 (7.9)
|
30 (2.2)
|
6 (0.4)
|
195 (14.2)
|
95% confidence interval
|
20.3, 24.7
|
8.2, 11.3
|
6.6, 9.4
|
1.5, 3.1
|
0.2, 1.0
|
12.5, 16.2
|
4 - 6 years; mature adult (n = 613)
|
70 (11.4)
|
43 (7.0)
|
37 (6.0)
|
8 (1.3)
|
0 (0.0)
|
30 (4.9)
|
95% confidence interval
|
9.1, 14.2
|
5.2, 9.3
|
4.4, 8.2
|
0.6, 2.6
|
0.0, 0.8
|
3.4, 6.9
|
≥ 7 years; senior (n = 659)
|
80 (12.1)
|
38 (5.8)
|
34 (5.2)
|
6 (0.9)
|
0 (0.0)
|
45 (6.8)
|
95% confidence interval
|
9.9, 14.9
|
4.2, 7.8
|
3.7, 7.1
|
0.4, 2.0
|
0.0, 0.7
|
5.1, 9.0
|
Percentages based on the number of positive dogs in that age group as the numerator and total of dogs reported to be in that category as denominator
Table 5: Number (%a) of dogs positive for intestinal parasites by coproantigen immunoassay or centrifugal flotationaccording to owner-reported current use of a heartworm/intestinal parasite control medication a
Demographic characteristic
|
Nematodes/ Giardia
|
Nematodes
|
Hookworm
|
Whipworm
|
Ascarid
|
Giardia
|
Dogs on medication: Yes (n = 2069)
|
404 (19.5)
|
155 (7.5)
|
125 (6.0)
|
31 (1.5)
|
11 (0.5)
|
276 (13.3)
|
95% confidence interval
|
17.9, 21.3
|
6.4, 8.7
|
5.1, 7.2
|
1.1, 2.1
|
0.3, 1.0
|
12.0, 14.9
|
Dogs on medication: No (n = 885)
|
190 (21.5)
|
101 (11.4)
|
84 (9.5)
|
25 (2.8)
|
6 (0.7)
|
106(12.0)
|
95% confidence interval
|
18.9, 24.3
|
9.5, 13.7
|
7.7, 11.6
|
1.9, 4.2
|
0.3, 1.5
|
10.0, 14.3
|
Medication status unknown (n = 52)
|
15 (28.9)
|
7 (13.5)
|
5 (9.6)
|
2 (3.9)
|
0 (0.0)
|
9 (17.3)
|
95% confidence interval
|
18.3, 42.4
|
6.4, 25.6
|
3.8, 21.0
|
0.3, 13.7
|
0.0, 8.2
|
9.2, 30.0
|
aPercentages based on the number of positive dogs in that demographic category as the numerator and total of dogs reported to be in that category as denominator
Coinfections were detected in 49 (1.6%) dogs. The most common coinfection was hookworm with Giardia in 24 dogs (0.8%), followed by hookworm and whipworm coinfection in 12 dogs (0.4%). Prevalence was also calculated by region (Table 6). In each region less than 1% of tests were positive for Cystoisospora. Details of the proportion of infected dogs and parks from which positive samples were collected in each of the 30 metropolitan areas are provided in supplemental Tables 1 and 2.
Table 6. Regional distribution: number (%) of dogs and parks with a positive test (coproantigen immunoassay or centrifugal flotation) for intestinal parasites
Positive tests
|
|
Nematodes/Giardia
|
Nematodes
|
Hookworm
|
Whipworm
|
Ascarid
|
Giardia
|
From dogs
|
Southeast (n = 989)
|
270 (27.3)
|
169 (17.1)
|
151 (15.3)
|
27 (2.7)
|
5 (0.5)
|
129 (13.0)
|
95% confidence interval
|
24.6, 30.2
|
14.9, 19.6
|
13,2, 17.7
|
1.9, 4.0
|
0.2, 1.2
|
11.1, 15.3
|
|
Northeast (n = 400)
|
72 (18.0)
|
25 (6.3)
|
21 (5.3)
|
8 (2.0)
|
1 (0.3)
|
48 (12.0)
|
95% confidence interval
|
14.5, 22.1
|
4.2, 9.1
|
3.4, 7.9
|
1.0, 4.0
|
0.0, 1.6
|
9.2, 15.6
|
|
Midwest (n = 708)
|
131 (18.5)
|
44 (6.2)
|
28 (4.0)
|
15 (2.1)
|
6 (0.9)
|
98 (13.8)
|
95% confidence interval
|
15.8, 21.5
|
4.7, 8.3
|
2.7, 5.7
|
1.3, 3.5
|
0.3, 1.9
|
11.5, 16.6
|
|
West (n = 909)
|
136 (15.0)
|
25 (2.8)
|
14 (1.5)
|
8 (0.9)
|
5 (0.6)
|
116 (12.8)
|
95% confidence interval
|
12.8, 17.4
|
1.9, 4.1
|
0.9, 2.6
|
0.4, 1.8
|
0.2, 1.3
|
10.7, 15.1
|
From parks
|
Southeast (n = 96)
|
86 (90.0)
|
73 (76.0)
|
69 (71.9)
|
25 (26.0)
|
5 (5.2)
|
70 (72.9)
|
95% confidence interval
|
81.7, 94.4
|
66.6, 83.5
|
62.1, 79.9
|
18.3, 35.7
|
2.0, 11.9
|
81.7, 94.4
|
|
Northeast (n = 39)
|
31 (79.5)
|
17 (43.6)
|
16 (41.0)
|
7 (18.0)
|
1 (2.6)
|
28 (71.8)
|
95% confidence interval
|
64.2, 89.5
|
29.3, 59.0
|
27.1, 56.6
|
8.7, 33.0
|
0.0, 14.4
|
56.1, 83.6
|
|
Midwest (n = 68)
|
59 (86.8)
|
33 (48.5)
|
26 (38.2)
|
12 (17.7)
|
5 (7.4)
|
50 (73.5)
|
95% confidence interval
|
76.5, 93.1
|
37.1, 60.2
|
27.6, 50.1
|
10.2, 28.5
|
2.8, 16.5
|
61.9, 82.6
|
|
West (n = 85)
|
67 (78.8)
|
20 (23.5)
|
14 (16.5)
|
8 (9.4)
|
5 (5.9)
|
65 (76.5)
|
95% confidence interval
|
68.9, 86.3
|
15.7, 33.6
|
10.0, 25.9
|
4.6, 17.7
|
2.2, 13.4
|
66.4, 84.3
|
See supplementary tables for detailed numbers by metropolitan region
Coproantigen immunoassay and centrifugal flotation
In detection of hookworm, whipworm, or ascarids, 289 infections were found (Fig 3). Of those, 162 (56.1%) were detected using CF and 244 (84.4%) using CAI. Both methods were in positive agreement in 117 (40.5%) of these infections. The combination of CF and CAI detected 78.4% more infections than did CF alone. For hookworm, the methods were in positive concordance for 85 infections (39.7% of detected hookworm infections), CAI detected 104 infections (48.6%) when CF was negative, and for 25 infections (11.7%) the reverse was true. Of the 58 Trichuris vulpis infections, the findings for each method were in positive concordance for 22 (37.9%), 18 infections (31.0%) detected by CAI were negative on CF, and 18 (31.0%) infections detected by CF were negative by CAI. For Giardia, the methods were in positive concordance for 38 infections (9.7%), 351 (89.8%) infections detected by CAI were negative on CF, and 2 (0.5%) infections detected by CF were negative on CAI.