Toxoplasma gondii infections are common in humans and animals worldwide. The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii infections in bears. Seroprevalence estimates of T. gondii in black bears (Ursus americanus) are one of the highest of all animals. In Pennsylvania, seroprevalence is around 80% and has remained stable for the past 4 decades. Approximately 3,500 bears are hunted yearly in Pennsylvania alone. The validity of different serological tests is discussed based on bioassay and serological comparisons. Seroprevalence in grizzly bears (Ursus arctos) is lower than that in black bears. Even polar bears (Ursus maritimus) are infected; infections in these animals are ecologically interesting because of the absence of felids in the Arctic. Clinical toxoplasmosis in bears is rare and not documented in adult animals. The few reports of fatal toxoplasmosis in young bears need confirmation. Viable T. gondii has been isolated from black bears and a grizzly bear. The genetic diversity of isolates based on DNA from viable T. gondii isolates is discussed. Genetic typing of a total of 26 T. gondii samples from bears using 10 PCR-RFLP markers revealed 8 PCR-RFLP ToxoDB genotypes: #1 (clonal type II) in 3 samples, #2 (clonal type III) in 8 samples, #4 (haplogroup 12) in 3 samples, #5 (haplogroup 12) in 3 samples, #74 in 5 samples, #90 in 1 sample, #147 in 1 sample, and #216 in 2 samples. These results suggest relatively high genetic diversity of T. gondii in bears. Overall, T. gondii isolates in bears range from those circulating in a domestic cycle (genotypes #1 and #2) to those mainly associated with wildlife (such as genotypes #4 and #5, together known as haplogroup 12). A patient who acquired clinical Trichinella spiralis infection after eating undercooked bear meat also acquired T. gondii infection. Freezing of infected meat kills T. gondii, including the strains isolated from bears.

弓形虫感染在全世界的人类和动物中都很常见。本综述总结了有关熊体内弓形虫感染的临床和亚临床感染流行率、流行病学和遗传多样性的全球信息。黑熊 ( Ursus americanus ) 中弓形虫的血清阳性率估计是所有动物中最高的之一。在宾夕法尼亚州，血清阳性率约为 80%，并且在过去 4 年中一直保持稳定。仅在宾夕法尼亚州，每年就有大约 3,500 头熊被猎杀。基于生物测定和血清学比较讨论了不同血清学测试的有效性。灰熊 ( Ursus arctos ) 的血清阳性率低于黑熊。连北极熊（Ursus maritimus ) 被感染；由于北极没有猫科动物，这些动物的感染具有生态学意义。熊的临床弓形虫病是罕见的，并且没有在成年动物中记录。少数关于年轻熊的致命弓形虫病的报告需要证实。可行的刚地弓形虫已从黑熊和灰熊中分离出来。讨论了基于活的刚地弓形虫分离株的DNA 的分离株的遗传多样性。共 26 只弓形虫的遗传分型使用 10 个 PCR-RFLP 标记的熊样本显示 8 个 PCR-RFLP ToxoDB 基因型：3 个样本中的 #1（克隆类型 II），8 个样本中的 #2（克隆类型 III），3 个样本中的 #4（单倍群 12），# 3 个样本中的 5（单倍群 12）、5 个样本中的 #74、1 个样本中的 #90、1 个样本中的 #147 和 2 个样本中的 #216。这些结果表明熊中弓形虫的遗传多样性相对较高。总体而言，熊体内的刚地弓形虫分离株范围从在家庭循环中传播的那些（基因型#1 和#2）到主要与野生动物相关的那些（例如基因型#4 和#5，统称为单倍群12）。一名在食用未煮熟的熊肉后获得临床旋毛虫感染的患者也感染了弓形虫感染。冷冻受感染的肉可以杀死刚地弓形虫，包括从熊身上分离出来的菌株。