1. Abstract accepted for 6th Asian Pig Veterinary Society congress, Ho Chi Minh City, Vietnam, September 23-25, 2013
TRYPANOSOMIASIS IN PIGS IN MALAYSIA
J.W. Lee1, C.Y.Tee1, B.K. Lim2, H.L. Too3 and P.Y. Choo4
1Rhone Ma Malaysia (M) Sdn Bhd, Selangor, Malaysia, 2Vet Food Agro Diagnostic (M) Sdn Bhd, Selangor, Malaysia, 3Merial Asia Pte. Ltd, 4Asia Pacific Special Nutrients (M) Sdn Bhd, Selangor, Malaysia
jinwee.lee@rhonema.com
Introduction
Although trypanosomes have been described in pigs, most are considered non pathogenic and of little economic importance1. In 1995, an outbreak of a disease in sows and boars, characterized by anorexia, abortions and deaths, ascribed to T. evansi was reported in a 180- sow-herd in Malaysia2. This is the only reported case of severe systemic disease due to trypanosomiasis in pigs.
The present study places on record an outbreak of trypanosomiasis with convincing evidence of the pathogenicity of T. evansi in pigs.
Material and Methods
Case History and Clinical Findings
In January 2012, a farrow-to-finish 1,000 sow herd consisting of Landrace-Large White hybrids and Duroc boars reported an outbreak of systemic disease involving nearly 40%-50% of sows and boars characterized by pyrexia, anorexia, abortions with almost 40% mortality in sows. The most dramatic manifestation was those of skin haemorrhages that ranged from patchy, echymotic to petechial in nature. The distribution of skin lesions appears to favour the ventral abdomen, lower extremities, the flank and also pressure points.
Autopsy findings
Autopsy of affected sows showed extensive streaks of haemorrhages in the muscles. Generalised haemorrhages were also seen in parenchymal organs. Liver cirrhosis, splenomegaly and multifocal hemorrhages were observed on both the renal cortex and medulla. Petechial and echymotic hemorrhages were also found on the myocardium, mitral valves, ureter and urinary bladder. There was severe bladder wall thickening. There was also generalized lymphadenopathy. The entire gross findings were reminiscent of a generalized bleeding disorder.
A preliminary diagnosis of classical swine fever was ruled out on epidemiological grounds as the breeding herd was routinely vaccinated and sows of all parities were involved. In addition, the production herd appeared unaffected.
Laboratory Findings
Based on previous experience with similar cases, a tentative diagnosis of trypanosomiasis was made. Five to 10 ml of blood in EDTA were collected from 20 clinically affected sows and submitted for hematological and parasitological examinations. During collection, the low viscosity (watery nature) of the blood was apparent. Fresh blood smear was done and examined under dark ground microscopy. On examination, active motile organisms resembling trypanosomes were observed.
Thick and thin blood smears as well as thin blood smears from the buffy coats in haematocrit tubes fixed in methanol and stained with 8% Giemsa were made, examined and were found to have trypanosomes. One ml of well mixed EDTA blood was inoculated into (Swiss Albino strain) mice for trypanosomes cultivation. The samples were then sent to University Putra Malaysia for further confirmatory diagnosis of Trypanosoma sp.
Haematological parameters showed regenerative anemia, thrombocytopenia, haemoconcentration, elevated liver enzymes and a marked hypoglobulinemia. All the inoculated mice were found dead on day 5 post inoculation. T. evansi was confirmed using the in-house Polymerase Chain Reaction (PCR) method.
Tabanid flies believed to be the vector for transmission of T. evansi from cattle to pigs were found to be prevalent in the farm. A blood smear taken from a tabanid fly caught in the farm also confirmed the presence of motile spiral organisms that were identified as T. evansi.
Discussion
Affected pigs treated with diminazine aceturate showed clinical improvements within a day. A second dose of Isometamidium chloride treatment was given at the dose of 1 gm per 1000kg 3 weeks later resulted in an immediate drop in clinical disease and mortality.
The disease was diagnosed as trypanosomiasis based on the clinical signs, presence of trypanosomes in the blood, laboratory diagnosis by PCR and inoculation test in mice and the response to both Diminazine aceturate and Isometamedium chloride.
Near the pig farm were palm oil plantations together with peripatetic cattle and buffaloes. It is believed that these animals could be asymptomatic carriers of T. evansi and the parasites were transmitted by biting flies especially Tabanids. In previous encounters with similar outbreaks in pigs (unpunblished), the presence of free- roaming cattle near the affected farm together with Tabanids in the farm were consistent epidemiological features. In all cases, treatment for trypanosomiasis invariably results in speedy recoveries.
Literature cited
1. Onah D.N., (1991) Tropical Animal Health Production 23 :141-147
2. Arunasalam et al., (1995) Jurnal Vet Malaysia. 7(2). 71-73.