Prepatent Period and Parasitemia in Leucocytozoon simondi Infections Resulting from Short Exposures to Sporozoites

Abstract

Of 38 Pekin ducklings infected with L. simondi by 24-hr exposures or intraperitoneal injection of ground-up black flies, 94.3% showed prepatencies of 7 days (? 24 hr). Most of the naturally infected ducks showed two peaks of gametocyte density, the first on the 10th day postexposure composed entirely of round forms, and the second on the 14th to 16th days postexposure composed of approximately 90% elongate forms. Elongate gametocytes appeared on the 11th day postexposure in 30 ducks, the 12th day in four ducks, and four did not show elongate forms. Eight ducks infected by injection of black flies died within 48 hr of the first appearance of elongate gametocytes, and ten ducks infected the same way showed a sharp increase in gametocyte density following the appearance of the elongate forms. The length of the prepatent period of Leucocytozoon simondi given by O'Roke (1934) and Fallis et al. (1951) is between 6 and 14 days. Several investigators have described the length of the initial infection to be about 30 days (O'Roke, 1934; Chernin, 1952b; Fallis et al., 1951). O'Roke (1934), Huff (1942), and Fallis et al. (1951, 1956) reported that the gametocyte population rose to a maximum density early, decreasing gradually into latency, and Chernin (1952a) pointed out that if there was any mortality the ducks died between 10 and 19 days postexposure. The pleomorphic gametocytes of L. simondi have been described by Fallis et al. (1951) and Chernin (1952b), who noted that round forms are most prominent early in patency while elongate or spindle forms predominate as the infection progresses. Chernin's (1952b) differential counts on the two forms show that the round form reaches a maximum density earlier than the elongate form. Chernin and Sadun (1949) thought that there might be a cyclic variation in the gametocyte density in primary infections, but Chernin (1952b) later refuted this. It is our intention to describe the occurrence and timing of the prepatent period, the appearance of elongate gametocytes, gametocyte density fluctuation, and mortality. Received for publication 14 March 1966. * Contribution Number 116 from the W. K. Kellogg Biological Station, Michigan State University. 962 MATERIALS AND METHODS Ducks were infected by exposure to black flies for 24 hr or sporozoites were inoculated intraperitoneally, thus allowing all sporozoite development to begin at approximately the same time. Thirty-eight white Pekin ducks ranging from 2 to 3 weeks of age were used as hosts for L. simondi. Group 1 consisted of 20 ducks exposed to black flies at Indian River, Michigan for 24 hr on 16 July 1964. Group 2 consisted of 18 ducks, of which ten were infected on 6 June 1965 by intraperitoneal injection of ground-up black flies collected at the Fox River in Seney, Michigan, on 3 June 1965, and eight were infected the salme way with black flies collected at the same location on 13 July 1965. All ducks were maintained in outdoor pens at the W. K. Kellogg Biological Station near Kalamazoo, Michigan, an area where L. simondi is not transmitted (Kocan and Clark, 1965). The naturally infected ducks of Group 1 were examined for parasites by thin blood films taken daily beginning with the day following exposure to black flies. Gametocyte densities were recorded every other day beginning with the 8th day postexposure. Ducks in Group 2 were sampled for gametocyte density daily. Blood for a slide and an erythrocyte count was obtained from a web vein puncture. Erythrocyte counts were done on a hemocytometer with blood diluted in a standard RBC diluting pipette, using Hayem's fluid as a diluent. All blood films were stained with Giemsa. Parasite counts were recorded as gametocytes per mm3 of venous blood. This was done by counting the mean number of gametocytes per 1 000 RBC's and the number of RBC's per mmm of blood. These values were used in the equation gametocytes _ RBC per mm3 gametocytes per mm 1,000 per 1,000 RBC's thus giving gametocytes per mm3 of blood. DifThis content downloaded from 157.55.39.120 on Sun, 04 Dec 2016 04:52:30 UTC All use subject to http://about.jstor.org/terms KOCAN AND CLARK-PREPATENT PERIOD AND PARASITEMIA IN LEUCOCYTOZOON TABLE I. Number of birds becoming patent and showing first elongate gametocytes on nth day postexposure. * Days postexposure 6 7 8 9 10 11 12