Spirocercosis in dogs in Israel: A retrospective case-control study (2004-2009)

- This is the largest case-control study of esophageal spirocercosis (ES) in dogs, overall including the geographical distribution of 442 such dogs in Israel.
- The incidence of ES in Israel increased compared to the 1990s, but remained rather constant during the study period.
- Spirocercosis has spread geographically in Israel compared to previous findings, despite prophylactic avermectin therapy administered by Israeli veterinarians in endemic areas, raising questions as to the efficacy of the currently employed preventive treatment protocol are insufficient. Nonetheless most dogs with ES did not receive any prophylactic treatment against the nematode.
- There were no differences in the seasonality and monthly incidence of ES, in contrast with previous findings, suggesting that spirocercosis is further established in Israel, becoming endemic.
- ES is significantly more common in sporting breed and large-breed dogs, in general, particularly in Retrievers, and is less common in toy-breed dogs.
- Vomiting and regurgitation were the most common clinical signs. However, the clinical presentation of ES highly varies, depending on disease stage, occurrence of aberrant migration and malignant transformation of the esophageal lesions.
- Hematology and serum chemistry finding in esophageal spirocercosis are non-specific.
- Endoscopy, radiography, coproscopy and necropsy findings are provided.

This case-control retrospective study (years 2004-2009) investigated the epidemiological, clinical, and diagnostic test findings of dogs with esophageal spirocercosis (ES) presented to the Hebrew University Veterinary Teaching Hospital (HUVTH) and coproscopy-positive dogs at the Kimron Veterinary Institute (KVI), Israel. It included 133 dogs with ES and 133 negative controls diagnosed at the hospital, and 343 dogs diagnosed at the KVI. The average incidence of ES at the HUVTH was 22.5/year, and the percentage of spirocercosis cases was stable at both institutions (HUVTH, 0.67-1.23%; KVI, 5-8%). Dogs aged >5 years old had 100-fold likelihood to be infected compared to dogs aged ≤1 year of age (P < 0.001). Mean body weight (P = 0.0004), proportion of Retrievers (P =0.002) and sporting breed dogs (P = 0.006) were higher, while proportion of toy breeds (P = 0.004) was lower in the ES group compared to the control group. The proportion of cases from Greater Tel-Aviv decreased (P = 0.002), while that of those from Judea and Jerusalem increased (P = 0.01) compared to the 1990s. Spirocercosis occurred in 22 dogs despite past prophylactic avermectin treatment. Vomiting and regurgitation were the most common clinical signs of ES. Coproscopy was S. lupi-positive in 33/60 dogs (55.0%). The median number of esophageal nodules was two (range 1-8), with a median diameter of 3.5 cm (range 1.0-11.0). Malignant esophageal lesion transformation was confirmed in 29 dogs (22%). Despite preventive attempts, spirocercosis has spread in Israel over time, compared to previous findings, raising questions about the efficacy of the currently accepted prophylactic protocol is incompletely effective.