How to Diagnose and Prevent Canine Clonorchiasis

Canine clonorchiasis is a parasitic disease caused by Clonorchis sinensis (C. sinensis) of the genus Clonorchis, family Opisthorchiidae, parasitizing the gallbladder and bile ducts of dogs. The disease is widely distributed in China, with reports from more than 20 provinces and municipalities, and it is most severe in the southern provinces. There have been few reports of this disease in the northern Liaoning region. Since the summer and autumn of 2001, the author has noticed that the disease occurs from time to time in this region and should be taken seriously.

1 Incidence

There are many dog-owning households in the suburbs of this city. The first case was seen in September 2001. The affected dog was female, about 4 months old, extremely emaciated, with slight sagging of the lower abdomen, passing brownish-black watery stool, vomiting, and pale and icteric mucous membranes. According to the owner, the dog was noticeably smaller and thinner than its littermates, and parasitism was suspected, so it had been dewormed with levamisole. One week earlier it had begun to show reduced appetite and diarrhea, and had been treated with antibiotics, but there was no improvement and the condition gradually worsened, so it was brought to the hospital. Symptomatic treatment including antiemetics, hemostatics and fluid replacement was given immediately, pending further examination for a definitive diagnosis, and the dog died the next morning. Necropsy and etiological examination confirmed a diagnosis of canine clonorchiasis. Most of the cases encountered afterward recovered after timely diagnosis and proper treatment.

2 Clinical Signs

The disease usually runs a chronic course. There are no obvious symptoms in mild infections; in heavy infections, the initial signs are listlessness, indigestion and poor appetite, and the condition gradually worsens, with vomiting, diarrhea, anemia and jaundice. In the later stage there is marked emaciation and cirrhosis, often with secondary ascites causing abdominal distension, and death often results if treatment is not given in time.

3 Necropsy Findings

The liver is enlarged, up to 2-3 times normal size, with an uneven surface covered with earth-yellow cysts of varying sizes; the gallbladder is enlarged, the bile is thick, and the bile ducts are thickened, with large numbers of live worms and eggs visible in the cysts, bile ducts and gallbladder; a small number of worms can be seen in the duodenum, the small intestinal mucosa is hemorrhagic, the intestinal wall is edematous, the stomach often contains a large amount of fluid containing dark brown flocculent material, and there is a variable amount of pale yellow fluid in the abdominal cavity.

4 Diagnosis

(1) The affected dog has been fed raw or undercooked freshwater fish and shrimp. (2) The affected dog is emaciated, depressed, anemic, jaundiced, with reduced appetite, indigestion, vomiting, and loose or bloody stool. The abdominal wall is tense, the liver region is sensitive on palpation, and the liver is enlarged and displaced caudally. (3) A definitive diagnosis can be made by finding eggs on fecal examination. Clonorchis sinensis eggs measure 29 x 17 micrometres, are yellow-brown, sunflower-seed-shaped or pear-shaped, have a lid at the top with a prominent shoulder, and contain a miracidium.

5 Prevention and Treatment Measures

(1) Praziquantel is a relatively ideal drug for treating clonorchiasis in dogs and cats; 50-75 mg per kg body weight orally, usually effective with a single dose, but it is best to give another dose after 5-7 days. In addition, drugs such as hexachloroparaxylene and albendazole may also be tried. (2) For dogs in the early stage of illness or with mild disease, 25% glucose, 5% sodium bicarbonate, compound sodium chloride, adenosine triphosphate, coenzyme A, and VB1 and VB12 can be used for treatment. (3) For dogs with more severe disease, in addition to the above methods, antiemetic and anti-inflammatory treatment should also be given. During treatment, note that for cases that have already developed hepatic ascites, intraperitoneal injection is not advisable. (4) Strengthen prevention by not allowing dogs to eat raw freshwater fish and shrimp; dogs kept beside fish ponds and ditches should be dewormed regularly and examined and treated; and the first intermediate host, freshwater snails, should be eliminated.

6 Points to Note

6.1 The disease is easily confused with icteric hepatitis, hemorrhagic gastroenteritis and other conditions, and attention should be paid to differentiation.

6.2 Clonorchis sinensis eggs are small and easily missed on direct smear, so fecal examination should use the water-washing sedimentation method or the formaldehyde-ether sedimentation method.

6.3 Dog owners generally have some awareness of regular deworming, but their understanding of the choice of deworming drugs is mostly unclear; they think levamisole can expel all kinds of internal parasites, which affects the early prevention and treatment of this disease. Guidance should be given on this point.

6.4 When dogs suffer from this disease, vomiting is often present, and orally administered deworming drugs are often vomited out; therefore, while using antiemetics, observe the dog carefully, and if the drug is vomited out, re-administer it promptly to ensure an effective dosage of the drug.