Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, SP, Brazil.
Vet Parasitol. 2011 Mar 10;176(2-3):151-6. doi: 10.1016/j.vetpar.2010.10.047. Epub 2010 Oct 30.
Neospora caninum is widely distributed in the world and this parasite is one of the major causes of abortion in cattle. Dogs and coyotes are definitive hosts of N. caninum and several species of domestic and wild animals are intermediate hosts. Dogs can become infected by the ingestion of tissues containing cysts and then excrete oocysts. It is not yet known whether sporulated oocysts are able to induce a patent infection in dogs, i.e. a shedding of N. caninum oocysts in feces. The objective of this study was to experimentally examine the infection of dogs by sporulated oocysts. The oocysts used in the experiment were obtained by feeding dogs with brain of buffaloes (Bubalus bubalis) positive for anti-N. caninum antibodies by indirect fluorescent antibody test (IFAT ≥200). Oocysts shed by these dogs were confirmed to be N. caninum by molecular methods and by bioassay in gerbils, and sporulated N. caninum oocysts were used for the oral infection of four dogs. The dogs were 8 weeks old and negative for antibodies to N. caninum and Toxoplasma gondii. Dogs 1 and 4 received an inoculum of 10,000 sporulated oocysts each; dog 2 an inoculum of 5000 sporulated oocysts and dog 3 received 1000 sporulated oocysts of N. caninum. The total feces excreted by these dogs were collected and examined daily for a period of 30 days. No oocysts were found in their feces. The dogs were monitored monthly for a 6-month period to observe a possible seroconversion and when this occurred the animals were eliminated from the experiment. Dogs 1 and 4 seroconverted 1 month after the infection with titer, in the IFAT, of 1600 and 800, respectively; the other two dogs presented no seroconvertion during the 6-month period. Dogs 1 and 2 were euthanized 180 days after infection and were examined for the detection of N. caninum in tissues (brain, muscle, lymph node, liver, lung, heart and bone marrow) by immunohistochemistry and PCR with negative results in both techniques. Bioassay in gerbils with brain of these dogs was also performed and again the results were negative. In conclusion, dogs infected with sporulated oocysts of N. caninum were not able to shed oocysts in feces. However, a higher dose of infection stimulated the production of antibodies against N. caninum in the dogs.
刚地弓形虫广泛分布于世界各地，是牛流产的主要原因之一。犬和丛林狼是刚地弓形虫的终末宿主，而多种家畜和野生动物是中间宿主。犬通过吞食含有包囊的组织而感染，之后排出卵囊。目前尚不清楚孢子化卵囊是否能在犬中引起显性感染，即粪便中排出刚地弓形虫卵囊。本研究的目的是通过实验检验孢子化卵囊对犬的感染。实验中使用的卵囊是通过用间接荧光抗体试验（IFAT≥200）检测为阳性的含抗刚地弓形虫抗体的水牛脑组织喂养犬而获得的。这些犬所排出的卵囊通过分子方法和在沙鼠中的生物测定被确认为刚地弓形虫，并用孢子化的刚地弓形虫卵囊对 4 只犬进行口服感染。这些犬 8 周龄，对刚地弓形虫和弓形虫均为抗体阴性。犬 1 和犬 4 各接种 10000 个孢子化卵囊；犬 2 接种 5000 个孢子化卵囊，犬 3 接种 1000 个刚地弓形虫孢子化卵囊。这些犬的总粪便排出物每天收集并检查 30 天。它们的粪便中均未发现卵囊。在接下来的 6 个月中，每月监测这些犬，观察是否出现血清学转换，如果出现则将动物从实验中淘汰。感染后 1 个月，犬 1 和犬 4 的间接荧光抗体试验滴度分别为 1600 和 800，出现血清学转换；而另外 2 只犬在 6 个月期间均未出现血清学转换。感染后 180 天，犬 1 和犬 2 被安乐死，用免疫组化和 PCR 技术在组织（脑、肌肉、淋巴结、肝、肺、心和骨髓）中检测刚地弓形虫，两种技术的结果均为阴性。用这些犬的脑组织进行沙鼠生物测定，结果也为阴性。综上所述，感染孢子化刚地弓形虫卵囊的犬未能在粪便中排出卵囊。然而，更高剂量的感染刺激了犬体内针对刚地弓形虫的抗体产生。
