Porcine Eperythrozoonosis in China

Transcription

1 Porcine Eperythrozoonosis in China JIANSAN WU, a JIANMIN YU, a CUIPING SONG, a SHENGJUN SUN, a,b AND ZHILIANG WANG a a National Exotic Animal Disease Center, Animal Quarantine Institute, Ministry of Agriculture, Qingdao , P.R. China b Department of Animal Medicine, Laiyang Agriculture College, Qingdao , P.R. China ABSTRACT: Eperythrozoonosis of swine (also designated as porcine mycoplasmosis) is a disease of swine under stress, expressed as a febrile condition with development of an acute ictero-anemia. It is caused by Eperythrozoon suis and usually causes a subclinical infection with a latent carrier state that persists for extended periods. In China, this disease has gradually developed as an important intercurrent disease and an emerging swine disease that, in recent years, has spread throughout all provinces except Tibet. Classical swine fever (hog cholera), porcine influenza, swine enzootic pneumonia, porcine reproductive and respiratory syndrome (blue ear disease), streptococci, and toxoplasmosis were detected in Eperythrozoonosis-infected pig herds, and caused serious economic losses. National epidemiology surveillance in 2002 revealed that this disease caused a total morbidity of 30% and a mortality of 10 20%. Total mortality (which includes culling sick pigs) was more than 60%. The morbidity within infected herds was near 100%, has spread throughout with a total mortality rate usually over 50%. Mortality of piglets in some districts was as high as 50%. The highest infection rate on pig farms was more than 90%. The farms with higher infection rates occurred in pig-raising areas during epidemic seasons. New diagnostic tests, such as ELISA and PCR, have been developed for the detection of porcine eperythrozoonosis, but traditionally the diagnosis of the disease is still based on clinical history and optical microscopic examination of the causative agent in blood smears. Efficient preventive and control measures include the detection of carriers in pig herds and treatment of sick pigs with drugs, such as long-acting oxytetracycline, doxycycline, or aceturate of diminazene. Oxytetracyclines as feed additives have been introduced for eperythrozoonosis prevention in uninfected pig herds, and pig producers have taken measures to reduce stress and improve sanitary conditions. KEYWORDS: porcine eperythrozoonosis; epidemiology surveillance; diagnosis; therapeneutics Address for correspondence: Prof. Jiansan Wu, National Exotic Animal Disease Center, National Animal Quarantine Institute, Ministry of Agriculture, , Qingdao, P.R. China. Voice: ; fax: wujians@public.qd.sd.cn Ann. N.Y. Acad. Sci. 1081: (2006). C 2006 New York Academy of Sciences. doi: /annals

2 WU et al.: PORCINE EPERYTHROZOONOSIS IN CHINA 281 INTRODUCTION Porcine eperythrozoonosis is a zoonotic disease caused by Eperythrozoon suis, and is likely to have worldwide distribution. Splitter and Williamson first recognized it in E. suis was formerly classified in the order Rickettsiales. Recently, on the basis of a comparison of 16s rrna gene sequences, it has been shown to belong to the Mycoplasmatales and has been included in the genus Mycoplasma, 2 but this classification at the genus level is disputed. 3 The disease is usually subclinical, but can on occasion produce a disease characterized by icterus, hemolytic anemia, fever, and weakness in neonatal and stressed feeder pigs; delayed estrus, early embryonic death, and abortions in late gestation. On most occasions the incidence of the clinical disease is low. Under stress, porcine eperythrozoonosis is expressed as a febrile condition with development of an acute ictero-anemia and observed in animals of all ages, from piglets to pregnant sows. 4 7 Swine eperythrozoonosis has been endemic in swineherds in China since the last century, and has been well recognized, especially since the 1990s. It has become an important new emerging intercurrent swine disease, causing serious economic losses to the swine industry in most provinces in China To date, swine eperythrozoonosis outbreaks have spread through most provinces except Tibet, and reports of epidemiology surveillance, clinical investigations, and research have greatly increased. Disease syndromes have been well recognized and it caused heavy morbidity and mortality in pig herds, resulting in serious economic losses to the swine industry. The present article intends to introduce briefly some information on prevalence and comprehensive control of swine eperythrozoonosis in recent years in China. MATERIALS AND METHODS Swine eperythrozoonosis was investigated through clinical symptoms and epidemiological surveillance combined with microscopical blood smear examination, and serology tests, such as IHA, ELISA, and PCR. The disease was controlled by treatment with several chemicals or prophylactic measures. Historical animal health records in the surveyed area were consulted, and national or regional epidemiological surveillances were carried out. Scientific research reports on swine eperythrozoonosis were consulted as a basis for the analysis. RESULTS The Pathogen The shape of the cell-wall-less organisms is round to oval, with disc and ring forms being common. The average diameter of M, and multiple

3 282 ANNALS NEW YORK ACADEMY OF SCIENCES organisms (of 10 or more) on one erythrocyte may be observed. Free organisms are sometimes seen in the blood plasma, tissue fluids, and cerebrospinal fluids. According to the observation with scanning and transmission electron microscopy, the surface of the erythrocyte membrane was affected and became rough with the erythrocyte appearing to have a hole in it. 12 Epidemiology This cell-wall-less uncultivated parasitic bacterium is thought to be transmitted from pig to pig by bloodsucking insects, including mosquitoes, ticks, and midges. Infection is usually subclinical, but on occasion it produces a disease characterized by icterus, hemolytic anemia, fever, and weakness in neonatal and stressed feeder pigs; delayed estrus, early embryonic death, and abortions. In most porcine eperythrozoonosis-affected herds other diseases were found, including classical swine fever (hog cholera), or other co-infections, such as porcine influenza, streptococci, swine enzootic pneumonia, pasteurellosis, porcine reproductive and respiratory syndrome (PRRS) (blue ear disease), or toxoplasmosis. A surveillance reported from 2002 revealed that E. suis infection was combined with classical swine fever (hog cholera), porcine influenza, or PRRS (blue ear disease) in Zhejiang, Fujian, Jiangsu, Anhui, Shan-dong, and Hebei provinces; as a main co-infection with classical swine fever and PRRS in Hunan, Hubei, Jangxi, Si-chuan, Chongqing, Shanxi, and Liaoning provinces and municipalities. The seasons of highest prevalence were May or June to November in 2001 with peaks from July to September, or March to October in 2002 with peaks from June to September. Outbreaks would occur associated with stress, caused by weaning, movement, and castration. In some endemic areas, the average infection and mortality rates of swine eperythrozoonosis in the national surveillance in 13 provinces and municipalities, involving 57 swine farms in 27 cities in 2002, was 30% and 10 20%, respectively. The total mortality rate (including culling of sick pigs) was over 60%. In some infected herds, the morbidity was 100%, with total death rates usually over 50%. The highest infection rate on any pig farm was more than 90%. The pig farms with higher infection rate occurred in pig-raising area in epidemic seasons. For example, in a village of southern China, where pig feed lots are on a large scale, morbidity of pigs was nearly 100%, with total mortality rates of 60%. Serious economic losses have been suffered in the swine industry in China. Pigs that recovered from swine eperythrozoonosis remain carriers of the disease. Pathogens persist in the circulating bloodstream but are not detected in blood films. The climatic factors contributing to the disease are high temperatures and high humidity. Stress, caused by weaning, movement, and castration is an important factor. In addition, in most affected herds other diseases were found, including classical swine fever, as well as co-infections, such as porcine influenza, streptococci, swine enzootic pneumonia, pasteurel-

4 WU et al.: PORCINE EPERYTHROZOONOSIS IN CHINA 283 losis, PRRS, or toxoplasmosis. Weaning, movement, and castration may induce clinical disease. The distribution of the disease in China has increased yearly. In , it was distributed in most provinces and municipalities, except Zhejang, Hainan, Sichuan, Guizhou, and Tibet. In 2002, it was distributed in all provinces and municipalities, except Tibet. Diagnosis Diagnosis of the disease is based on clinical history, post-mortem findings, and optical microscopic examination of the causative agent in blood smears. The disadvantage of blood smear detection is that it is only effective in the acute stage, but in latent carriers the pathogen may be missed. Some tests have been developed for the detection of swine eperythrozoonosis The immunofluorescene assay test was reported to be 40% more sensitive than microscopic examination. An ELISA with horseradish peroxidase-staphylococcal protein as the second antibody was sensitive and specific. It is operated on nitrocellulose membranes; the result was easy to judge with the naked eye. PCR has been established for surveillance. In order to probe into the effect of E. suis on the immunity level in piglets, the red blood cell (RBC) C3b receptor rosette rate, the RBC immune complete rosette rate, the lymphocyte transformation rate, and the formation rate of EA rosettes and EAC rosettes were used. 19,20 All the data obtained in artificially infected piglets were significantly lower than in healthy ones (P < 0.001). Therefore, E. suis can impede the immune function of piglets. These experiments revealed that the entire immune function was diminished as the quantity of C3b receptors and T lymphocytes changed. This may explain the intercurrent infections of virus pathogens in the infected herds. Research on the effects of E. suis on the antioxidant function confirmed that E. suis could cause the low antioxidant ability, increased accumulation of NO and oxygen-free radicals, and the strengthening reaction of lipoperoxidation, which is one of the causes of serial pathological lesion. Treatment and Control The detection and treatment of carriers is an efficient method for the control of swine eperythrozoonosis. 11,12,21 Clinical records confirm the effect of longacting oxytetracycline, doxycycline, and aceturate of diminazene. The cure rate with doxycycline appeared to be higher than that of aceturate of diminazene, and may be due to its ability to enter the fetus in the uterus. Hematinics are beneficial feed additives for recovery from the infection. Although injections of long-active oxytetracycline are probably the most effective, they are often not practical because of the high cost and the labor input required. Some commercial productions including traditional Chinese herb medicines have

5 284 ANNALS NEW YORK ACADEMY OF SCIENCES been used in the disease control, but recovered animals frequently become re-infected and the cost of treatment is higher than can be really justified. As a preventative treatment, oxytetracycline as a feed additive has been introduced for the prevention of eperythrozoonosis in clean pig herds. Individual producers and swine farm owners have increased efforts toward reducing stress, and improving pig sanitary conditions. DISCUSSION AND CONCLUSION Swine eperythrozoonosis has become a newly emerging disease in China. Because of significant increases in prevalence in this country except in Tibet, it has caused heavy economic losses in the swine industry and the disease poses a potential threat to pig producers. E. suis can cause a diminished immune function, and has become a very important factor contributing to co-infection with other pathogens in pig herds in China. E. suis is still an uncultivated pathogen, and protective antibodies do not develop effectively following infection. The use of live vaccines using these fragile pathogens is not an adequate control strategy and cannot be based on the development of live vaccines. New idea strategies for the current protection of pigs in endemic areas should be developed. The exact economic importance should be more accurately surveyed. Reliable diagnostic methods that are easy to operate, should be developed for field use. There is a need to establish and standardize them for the identification of pathogens and use in epidemiological investigations. Molecular analysis of E. suis should be persued toward the development of subunit and genetic vaccines or, if possible, multivalent vaccines. ACKNOWLEDGMENTS The authors gratefully thank Dr. Gerrit Uilenberg, Editor of the Newsletter on Ticks and Tick-borne diseases of Livestock in the tropics, a publication of the ICTTD-3 program, Coordination Action project No , funded by the International Cooperation Program of the EU, for his advice and manuscript review. We are very grateful to Dr. Jean-Charles Maillard for his valuable comments and suggestions. We would also like to thank Professor Hu Ouxiang, Editor of the Chinese Journal of Animal Quarantine, for his friendly manuscript checking. REFERENCES 1. SPLITTER, E.J. & R.L. WILLIAMSON Eperythrozoonosis in swine: a preliminary report. J. Am. Vet. Med. Assoc. 116: NEIMARK, H., K.-E. JOHANSSON, Y. RIKIHISA & J.G. TULLY Proposal to transfer some members of the genera Haemobartonella and Eperythrozoon to the

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