Improved Diagnosis of Low Intensity Spirocerca Lupi Infection by the Sugar Flotation Method

Spirocerca lupi, a spirurid nematode, is commonly found in dogs and other carnivores mainly in tropical and subtropical areas. For the last 4 decades, spirocercosis has rarely been diagnosed in Israel, although its prevalence in many other Mediterranean countries is high. However, since 1 989 the incidence of infection with S . lupi in Israel has sharply increased. S tudies of histories of dogs in which spirocercosis was diagnosed postmortem have shown that all cases came from a specific area in the Tel Aviv region. To confirm the existence of S . lupi in this area, fecal samples were collected from dogs and park lawns and examined for the presence of S . lupi eggs. Laboratory diagnosis of S . lupi infection in live dogs based on finding the very small embrionated eggs (35 x 1 5 m) in the feces has been problematic. Because of their small size, the eggs are difficult to detect in the direct preparation and in the sediments obtained by concentration methods. Except for flotation in 33% zinc sulfate, the commonly used salt and sugar solutions have been reported as ineffective for flotation of the eggs. ,4 The only method presently used for routine diagnosis and epidemiologic studies ,3 is a dilution method using artificial gastric juice (AGJ). However, because this method involves considerable dilution of the fecal sample, we decided to reinvestigate the sugar flotation technique, particularly for low-intensity infections. Twenty fecal samples from dogs with differing levels of S . lupi infection were examined. Five grams of feces was thoroughly mixed in 75 ml tap water and strained through a wire screen. From each sample, 5 replicate tubes, each containing 1 5 ml of suspension, were centrifuged at 2 ,000 RPM for 1 0 minutes. The sediments in the 1 st and 2nd tubes were resuspended in 5 ml of AGJ (2% pepsin, 1 % concentrated hydrochloric acid in saline) and in 5 ml water, respectively. After 1 0 minutes, 2 samples of 0.05 ml were removed from each tube with a pipette and examined at 1 00 x magnification. The sediments in the 3 remaining tubes were resuspended in a sugar solution (specific gravity 1 .27), filled to the rim, covered with an 1 8 x 1 8-mm coverslip, and centrifuged in a swinging-head centrifuge at 2 ,000 RPM for 5, 1 0, and 20 minutes, respectively. Cover slips were transferred face down to the slides and examined over the entire area at 1 00 x magnification. The number of eggs counted was designated as the eggs per gram (epg) value. Results of S . lupi detection by both dilution and sugar flotation techniques are shown in Table 1 . In most samples, the AGJ dilution technique gave higher egg counts than did the water dilution. Compared with the sugar flotation, the AGJ dilution method also gave higher computed epg counts