Weight Development of Intermediate Hosts Infected by Cystoisospora ohioensis-Like Species (Apicomplexa: Cystoisosporinae): Experimental Model in Mice

This study aimed to evaluate clinical signs, visceral changes, and weight development in intermediate hosts infected with Cystoisospora ohioensis-like oocysts from naturally infected dogs. Using 135 albino mice divided into three groups—INFECTED (inoculated with oocysts), PAIR-FED (given the same food as infected mice), and CONTROL (fed ad libitum)—researchers monitored weight and pathological changes over 35 days. Mice were euthanized at various intervals post-inoculation (1–35 days), with organs from some INFECTED mice fed to dogs on day 60 for a biological assay. The INFECTED group showed higher body weight and weight gain than the CONTROL group, though organ weights were greater, leading to lower carcass yield. Tissue cysts with hypnozoites were found in the intestines (1st day), Peyer’s patches (up to 5th day), and lymph nodes/spleen (up to 35th day). Dogs inoculated with hypnozoites (from infected mice) had a shorter prepatent period, longer patent period, and higher oocyst shedding compared to those given sporulated oocysts. The findings indicate that C. ohioensis-like species affect mouse weight, persist in visceral tissues for up to 60 days, and exhibit biological differences in infectivity between sporozoites and hypnozoites in dogs.