S dentatus Diesing 1839
S. dentatus occurs in capsules in perirenal fat and in the walls of the ureter and adjacent tissues of swine. Capsules containing adult worms communicate by channels with the ureters or the renal pelvis, and eggs of the parasite can pass into the urine and leave the body of the host (Fig. 3.4). According to Alicata (1935b) eggs were 91-114 X 53-65 mm in size and composed of 32-64 cells when passed in urine. Eggs developed to first-stage larvae and hatched in 1-2 days. First-stage larvae moulted in 20 h at 22-24°C when they were 530 mm in length. In 70 h second-stage larvae moulted to the third stage and were 518-610 mm in length (excluding the sheath, which is the second-stage cuticle with its attenuated tail).
Infective larvae survived in soil with faeces in the laboratory for 108 days (Ross and Kauzal, 1932) but Spindler (1934) reported that larvae survived for only 76 days under field conditions and were not resistant to low temperatures, dry conditions or exposure to sunlight. Larvae were negatively phototactic and positively thermotactic. However, during early morning when dew was present larvae were found on blades of grass.
Tromba (1955) gave eggs to earthworms (Eisenia foetida) and subsequently found unsheathed larvae in the lumen of the intestine of most of them. Some larvae were noted in masses of amoebocytes called 'brown bodies'. Earthworms harboured larvae for up to 35 days and pigs given earthworms containing larvae became infected. Batte et al.
Third-stage larva Second-stage larva First-stage larva
Fig. 3.4. Development and transmission of Stephanurus dentatus. I = intestine; K = kidney;
LI = liver; ML = mesenteric lymph node; O = oesophagus; S = stomach; UB = urinary bladder.
Third-stage larva Second-stage larva First-stage larva
Fig. 3.4. Development and transmission of Stephanurus dentatus. I = intestine; K = kidney;
LI = liver; ML = mesenteric lymph node; O = oesophagus; S = stomach; UB = urinary bladder.
(1960) confirmed the observations of Tromba (1955). Sinha (1967) infected the earthworms Eutypheus waltoni and Pheretima sp.
The behaviour of the parasite in swine has been investigated by Bernard and Bauche (1914), Schwartz and Price (1929, 1931, 1932), Ross and Kauzal (1932), Spindler (1934), Batte et al. (1960) and Waddell (1969), who reported that swine could become infected by ingesting infective larvae or by the penetration of larvae through the skin, especially abraded skin. They also showed that larvae developed for a time in the liver before invading the ureters and kidneys.
Lichtenfels and Tromba (1972) carried out a careful study in which the larval stages were identified. They gave 2000-20,000 infective larvae to 6-8-week-old pigs which were subsequently examined for worms at various intervals. Larvae exsheathed in the gut and most larvae entered lymphatic vessels and were found in mesenteric lymph nodes as early as 1 day postinfection. Larvae moulting to the fourth stage were found in the nodes as early as 3 days. They appeared in the liver in 10 days and were in the early fourth stage at this time. Moulting fourth-stage larvae and subadult worms were present in the liver 31 days postinfection. The authors concluded that only larvae which had developed in lymph nodes 'contributed substantially to the fourth-stage and adult worms found in the host following infection'.
According to Schwartz and Price (1929, 1931, 1932) worms which had completed their development in the liver perforated the liver capsule and invaded the peritoneal cavity about 77 days postinfection. Worms migrated to the perirenal regions in about 107—113 days and invaded perirenal fat. In the latter, worms burrowed towards the ureters, which they perforated and entered and within which they became encapsulated. Some worms wandered from the ureters into the kidney pelvis and under the kidney capsule. According to Batte et al. (1960) worms may spend 4—9 months in the liver before moving to the ureters and the prepatent period was 9—16 months. Batte et al. (1966) reported that sows may pass eggs for at least 3 years following an initial infection. These authors also gave larvae to pregnant gilts (young females) and demonstrated transplacental transmission.
Ross and Kauzal (1932) allowed larvae to penetrate the skin of guinea pigs and reported that larvae remained in the skin for 7 days and underwent the third moult. Fourth-stage larvae appeared in the liver in 3-40 days and underwent the fourth moult in 2 months. In about 6 months they migrated directly to the ureters and produced eggs.
In pigs, aberrant fourth-stage and subadult S. dentatus may wander in tissues and be found encapsulated in the pancreas, heart, lungs, spleen and skeletal muscles. They may rarely invade the central nervous system and cause paralysis. The parasite has been reported sporadically in cattle, which are liable to ingest larvae crawling on vegetation.
S. dentatus is regarded as an important pathogen of swine, resulting in destruction of liver tissue, thrombosis of hepatic vessels, cirrhosis, peritonitis and cystitis. Infection significantly reduces weight gains in piglets. Also, the parasite may transfer to cattle and cause liver damage.
Steward and Tromba (1957) took advantage of the long prepatent period and the rapid growth of pigs to control the infection. They recommended that breeding be confined to gilts and that the latter should be marketed after weaning their first litters. There would be, therefore, little or no opportunity for transmission to occur between the sow and her young and in a short time the parasites could be eliminated from the swine.
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