Evaluation of a Vaccine Candidate Isolated from Oocyst in Mice

Background And Aim: Cryptosporidiosis is a leading cause of diarrheal disease worldwide and is an animal and public health burden. This study aimed to evaluate the protective potential of affinity-purified oocyst antigen as a vaccine candidate according to fecal oocyst shedding, humoral and cellular immune responses, histopathological changes, and the number of parasite developmental stages in ileal and hepatic tissues.

Materials And Methods: We isolated oocysts from naturally infected buffalo calves and identified them molecularly as isolates (GenBank: ON730707 and ON730708) by targeting the oocyst wall protein gene. We propagated the oocysts in mice. In addition, we prepared crude antigen from the isolated oocysts by purification using cyanogen bromide-activated Sepharose-4B affinity chromatography coupled with rabbit hyperimmune serum. Then, we divided 81 parasite-free mice into three groups: (1) non-vaccinated non-infected mice, (2) mice orally infected with 1 × 10 oocysts on week 4 of the experiment, and (3) mice immunized twice with 40 μg/kg of the purified fraction at 2-week intervals. Then, we challenged the vaccinated group with oocysts after 2 weeks, and the positive control group was infected at the same time.

Results: We observed a prolonged prepatent period and decreased oocyst shedding in the vaccinated infected mice compared with the non-vaccinated infected mice (t < 0.001). The vaccinated mice had significantly higher immunoglobulin G levels than those in the other two groups at all examined weeks. In addition, the production of cytokines interferon-gamma, interleukin (IL)-10, IL-12, and IL-15 was activated post-vaccination. After the challenge, all tested cytokines were significantly increased (p < 0.001) in the two infected groups compared with the non-vaccinated non-infected group, with the highest levels in the vaccinated infected group. Vaccinated infected mice exhibited significantly fewer pathological lesions in the ileum and liver than non-vaccinated infected mice, which showed prominent histopathological lesions. Endogenous developmental stages of indicated that the ileum was more parasitized than the liver and that vaccination resulted in a lower number of oocysts in ileal and hepatic tissues (p < 0.05).

Conclusion: Our prepared affinity-purified vaccine candidate could be promising in protecting against cryptosporidiosis.