Diagnostic Methods and Prevention and Control Measures for Swine Leptospirosis

At a pig farm in Shuimogou District, Urumqi City, a disease characterized by jaundice, hemoglobinuria, and subcutaneous edema broke out. Based on epidemiology, necropsy changes, bacteriological examination, and animal experiments, it was diagnosed as swine leptospirosis. The report is as follows.

1 Outbreak situation

Wang, a farmer in Shuimogou District, Urumqi City, raised 147 growing pigs with an average weight of 40-50 kg. One pig died suddenly, 3 died 2 days later, 2 died 3 days later, and by 12 days later, a total of 34 had died, with a mortality rate of 23.2%. The owner claimed that due to newly built pens, the floor was damp, and the barn temperature was 20-22 degrees C. After the outside temperature dropped, the number of rats increased markedly, and they frequently entered and exited the feed troughs.

2 Clinical symptoms

The body temperature of the sick pigs rose to about 40.5-41.5 degrees C. They were listless, refused feed, had convulsions, swayed, and were unsteady when standing; some were constipated, and some had diarrhea; urine was tea-colored or blood-colored; the skin was pale yellow; the conjunctiva and sclera were icteric; among the dead pigs, 4 had edema of the face, submandibular area, and neck; the 6 pigs that died in the early stage all died acutely, and the others all died within 2-3 days after the rise in body temperature.

3 Necropsy changes

The skin was pale yellow, the muscles were anemic, there was subcutaneous edema of the neck, and the subcutaneous fat was yellow-stained; there was effusion in the thoracic cavity and pericardium, with occasional hemorrhagic spots on the endocardium; the blood was thin; the lungs were enlarged and earth-yellow; the gallbladder was distended; the mesenteric lymph nodes were enlarged; occasional punctate grayish-white necrotic foci were seen in the kidneys; the stomach wall was edematous; the bladder accumulated urine that was tea-colored or blood-colored.

4 Laboratory examination

(1) Aseptically collected heart blood, pleural fluid, liver, and kidney tissues were compressed into smears and examined by dark-field microscopy, revealing rod-shaped leptospires of various forms, actively motile, with one or both ends curved into a hook. Aseptically collected heart blood, liver, spleen, and kidney tissues from sick pigs slaughtered in the moribund stage were smeared, stained by the silver impregnation method, and examined by dark-field microscopy, revealing large numbers of filamentous, brown-black, round rod-shaped bodies with one or both ends curved into a hook.

(2) Aseptically collected heart blood, liver, kidney, and spleen tissues were inoculated into Schiffner's culture medium and cultured at 25 degrees C, with observation every 5 days. At about 15 days, slight opalescence appeared, followed by dark-field microscopic examination, with results the same as those of the diseased material smears.

(3) The above Schiffner's culture medium that was positive by microscopy was injected intraperitoneally into 5 guinea pigs weighing about 150-200 g under strictly isolated conditions, and another 5 guinea pigs of equal weight were set as controls and injected intraperitoneally with 0.25 ml of Schiffner's culture medium. As a result, the control group remained healthy and alive after 7 days; the experimental group gradually showed elevated body temperature 24 h after inoculation, exceeding normal by 0.5-1.0 degrees C, listlessness, anorexia, icteric conjunctiva, pale yellow skin, and hemoglobinuria, and all died within 120 h. Necropsy showed typical yellow staining of the subcutaneous tissue and skin, enlarged earth-yellow liver, enlarged kidneys with scattered necrotic foci, and tea-colored or blood-colored accumulated urine in the thoracic fluid, abdominal fluid, and bladder.

(4) Aseptically collected heart blood, liver, spleen, and kidney tissues were compressed into smears and directly examined by dark-field microscopy, revealing large numbers of filamentous, motile, rod-shaped bodies with one or both ends curved into a hook. Based on comprehensive analysis of epidemiology, clinical symptoms, necropsy changes, etiological examination, and animal experiments, it was diagnosed as swine leptospirosis.

5 Prevention and control measures

(1) Doxycycline, 20 mg/kg body weight per day, mixed into feed, for 7 consecutive days.

(2) Junbizhi (gentamicin sulfate + TMP) 10 mg/kg body weight per day, 2 times/day, intramuscular injection, for 5 consecutive days.

(3) Oral rehydration salts, 295 g pack, 10 bags per day, in drinking water, for 7 consecutive days.

(4) Thoroughly clean the pens, disinfect with 0.1% sodium hydroxide for 7 days, and spread cinder dust to absorb moisture and water.

(5) Put out rat poison "Sujian" throughout. After the above treatment, pig deaths stopped 12 days later.