Monis P T, Andrews R H, Mayrhofer G, Mackrill J, Kulda J, Isaac-Renton J L, Ey P L
Department of Microbiology and Immunology, University of Adelaide, Australia.
Parasitology. 1998 Jan;116 ( Pt 1):7-19. doi: 10.1017/s0031182097002011.
Infection of suckling mice with Giardia trophozoites recovered from the intestines of 11 dogs autopsied in Central and Southern Australia in each case produced an established isolate. In contrast, only 1 isolate was obtained by inoculation of faecal cysts. The organisms grew poorly in comparison with isolates from humans or non-canine animal hosts. Light microscopy revealed that the trophozoites had median bodies with the 'claw hammer' appearance typical of G. intestinalis (syn. G. duodenalis, G. lamblia) but that they differed in shape and nuclear morphology from axenic isolates of human or canine origin. Allozymic analysis of electrophoretic data representing 26 loci and phylogenetic analysis of nucleotide sequences obtained from DNA amplified from the glutamate dehydrogenase locus showed that the 11 isolates examined from Australian dogs were genetically distinct from all isolates of G. intestinalis that have been established previously from humans and animals, and also from G. muris. Both analytical methods placed 10 of the Australian canine isolates into a unique genetic lineage (designated Assemblage C) and the eleventh into a deep-rooted second branch (designated Assemblage D), each well separated from the 2 lineages (Assemblages A and B) of G. intestinalis that encompass all the genotypes known to infect humans. In contrast, 4 axenic isolates derived from dogs in Canada and Europe (the only other isolates to have been established from dogs) have genotypes characteristic of genetic Assemblages A or B. The findings indicate that the novel Giardia identified in these rural Australian dogs have a restricted host range, possibly confined to canine species. The poor success rate in establishing Giardia from dogs in vitro suggests, further, that similar genotypes may predominate as canine parasites world-wide. The absence of such organisms among isolates of Giardia that have been established from humans by propagation in suckling mice indicates that they are unlikely to infect humans. However, infection of humans by those dog-derived genotypes that grow in vitro cannot be excluded.
用从澳大利亚中部和南部剖检的11只犬肠道中回收的贾第虫滋养体感染乳鼠，在每种情况下均产生了一个稳定的分离株。相比之下，通过接种粪便包囊仅获得1个分离株。与来自人类或非犬类动物宿主的分离株相比，这些生物体生长较差。光学显微镜检查显示，滋养体具有中体，呈肠贾第虫（同义词：十二指肠贾第虫、蓝氏贾第虫）典型的“羊角锤”外观，但它们在形状和核形态上与来自人类或犬类的无菌分离株不同。对代表26个基因座的电泳数据进行的等位酶分析以及对从谷氨酸脱氢酶基因座扩增的DNA获得的核苷酸序列进行的系统发育分析表明，从澳大利亚犬中检测的11个分离株在遗传上与先前从人类和动物中建立的所有肠贾第虫分离株以及鼠贾第虫不同。两种分析方法都将10个澳大利亚犬分离株归入一个独特的遗传谱系（指定为集合C），第11个归入一个深根的第二分支（指定为集合D），每个分支都与包含所有已知感染人类基因型的肠贾第虫的两个谱系（集合A和B）相距甚远。相比之下，来自加拿大和欧洲犬的4个无菌分离株（唯一其他已从犬中建立的分离株）具有遗传集合A或B的基因型特征。这些发现表明，在这些澳大利亚农村犬中鉴定出的新型贾第虫宿主范围有限，可能仅限于犬类。从犬体外培养贾第虫的成功率较低进一步表明，类似的基因型可能在全球犬类寄生虫中占主导地位。在通过乳鼠传代从人类中建立的贾第虫分离株中没有此类生物体，这表明它们不太可能感染人类。然而，不能排除那些在体外生长的源自犬的基因型感染人类的可能性。
