Dubey J P, Sundar N, Pineda N, Kyvsgaard N C, Luna L A, Rimbaud E, Oliveira J B, Kwok O C H, Qi Y, Su C
United States Department of Agriculture, Agricultural Research Service, Animal and Natural Resources Institute, Animal Parasitic Diseases Laboratory, Building 1001, Beltsville, MD 20705-2350, USA.
Vet Parasitol. 2006 Nov 30;142(1-2):47-53. doi: 10.1016/j.vetpar.2006.06.016. Epub 2006 Jul 28.
The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 98 free-range chickens (Gallus domesticus) from Nicragua was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT), and found in 84 (85.7%) of 98 chickens with titers of 1:5 in 10, 1:10 in eight, 1:20 in seven, 1:40 in nine, 1:80 in 11, 1:160 in one, 1:200 in 27, 1:400 in six, 1:800 four, and 1:3200 in one bird. Hearts and brains of 32 chickens with titers of 1:10 or less were pooled and fed to three T. gondii-free cats. Hearts and brains of 66 chickens with titers of 1:20 or higher were bioassayed in mice. Feces of cats were examined for oocysts. The cat fed tissues from eight chickens with titers of 1:10 shed T. gondii oocysts. The two cats fed tissues of 24 chickens with titers of 1:5 or less did not shed oocysts. T. gondii was isolated by bioassay in mice from 47 chickens with MAT titers of 1:20 or higher. All infected mice from six isolates died of toxoplasmosis. Overall, 41 of 170 (24.1%) mice that became infected after inoculation with chicken tissues died of toxoplasmosis. Genotyping of these 48 isolates (47 from mice and 1 from pooled tissues) using polymorphisms at the loci SAG1, SAG2, SAG3, BTUB and GRA6 revealed eight genotypes. Six isolates had Type I alleles, three isolate had Type II alleles and six isolates had Type III alleles at all loci. Four isolates had mixed infections. Two isolates have a unique allele at SAG1 locus and combination of I and III alleles at other loci. The rest 27 isolates contained the combination of Type I and III alleles and were divided into four genotypes. More than one genotypes were often isolated in chickens from the same household, indicating multiple genotypes were circulating in the same environment. This may explain the high frequency of mixed infections observed. High rate of mixed infection in intermediate hosts such as chickens may facilitate genetic exchange between different parasite lineages in definitive feline hosts. This is the first report of genetic characterization of T. gondii isolates from Nicragua, Central America.
散养鸡中弓形虫的感染率是土壤中弓形虫卵囊感染率的良好指标，因为鸡在地面觅食。对来自尼加拉瓜的98只散养鸡（家鸡）的弓形虫感染率进行了测定。采用改良凝集试验（MAT）检测弓形虫抗体，在98只鸡中有84只（85.7%）检测到抗体，抗体效价分别为：1:5的有10只，1:10的有8只，1:20的有7只，1:40的有9只，1:80的有11只，1:160的有1只，1:200的有27只，1:400的有6只，1:800的有4只，1:3200的有1只。将32只抗体效价为1:10及以下的鸡的心脏和大脑混合后喂给3只无弓形虫的猫。将66只抗体效价为1:20及以上的鸡的心脏和大脑在小鼠中进行生物测定。检查猫的粪便中是否有卵囊。喂食了8只抗体效价为1:10的鸡组织的猫排出了弓形虫卵囊。另外两只喂食了24只抗体效价为1:5及以下的鸡组织的猫未排出卵囊。通过生物测定在小鼠中从47只MAT效价为1:20及以上的鸡中分离出了弓形虫。来自6个分离株的所有感染小鼠均死于弓形虫病。总体而言，170只接种鸡组织后感染的小鼠中有41只（24.1%）死于弓形虫病。利用SAG1、SAG2、SAG3、BTUB和GRA6位点的多态性对这48个分离株（47个来自小鼠，1个来自混合组织）进行基因分型，共发现8种基因型。6个分离株在所有位点均具有I型等位基因，3个分离株具有II型等位基因，6个分离株具有III型等位基因。4个分离株为混合感染。2个分离株在SAG1位点有独特等位基因，在其他位点为I型和III型等位基因组合。其余27个分离株包含I型和III型等位基因组合，分为4种基因型。同一家庭的鸡中常分离出不止一种基因型，表明同一环境中有多种基因型在传播。这可能解释了观察到的高混合感染率。鸡等中间宿主中的高混合感染率可能促进终末宿主猫体内不同寄生虫谱系之间的基因交换。这是中美洲尼加拉瓜弓形虫分离株基因特征的首次报告。
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