Experiment 1: Inoculation Methods and Results

In Experiment 1, various inoculation methods were tested to assess their effect on the infection rates of Histomonas meleagridis. The most effective method was intracloacal inoculation (CIM), resulting in a startling 100% infection rate. In contrast, oral inoculation using culture media (OIM) yielded the lowest infection rate at just 8.7%. Interestingly, oral inoculation with cecal content (OICC) produced a moderate infection rate of 43%, significantly higher than that of the OIM group (Table 2; P = 0.0003).

The mortality rates depicted a similar hierarchy: nestimated at 88% for the CIM group, compared to 7% in OIM and 15% in OICC (Table 2; P = 0.0025). This pattern continued with higher liver and ceca lesion scores in the CIM and OICC groups when compared to the OIM group (Table 2, P = 0.0018; Table 2, P = 0.0003).

To validate these findings, a second experiment (Experiment 2) was conducted in isolator cages, focusing on the CIM and OICC methods. Results indicated that the oral inoculation (OI) reached a 90% infection rate, displaying no significant difference from the cloacal inoculation (CI; Table 3, P = 0.6433).

Mortality and lesion scores for both OI and CI groups showed no significant variance (Table 3).

Analysis and Implications of Experiment Findings

In this experiment, three inoculation methods—cloacal inoculation (CIM), oral inoculation with H. meleagridis in culture (OIM), and oral inoculation with H. meleagridis in cecal content (OICC)—were compared. The study established that cloacal inoculations remained the most effective, corroborating previous research by Hu et al. (2004). Notably, the reverse peristalsis of birds allows for a higher infection rate through cloacal inoculation, presenting significant advantages for laboratory studies.

Challenges with Oral Inoculation

It is essential to address the challenges encountered with oral inoculation methods. The low infection and mortality rates associated with OIM can be linked to the acidic environment in turkeys’ proventriculus and ventriculus, which endures markedly low pH levels, impeding the survival of H. meleagridis. Conversely, the enhanced infection rates observed with OICC can be attributed to the protective qualities of cecal contents, mitigating exposure to harsh gastric conditions. Previous research also validates the necessity of bacteria in facilitating H. meleagridis infections in gnotobiotic turkeys, suggesting a symbiotic relationship that warrants further exploration.

Insights from Experiment 2

Remarkably, Experiment 2 demonstrated an even higher infection rate (90%) for the oral infection group compared to the 43% from Experiment 1, which raises questions regarding the consistency of cecal content and its impact on infection rates. The fresh cecal content utilized in Experiment 2 may have featured a different viscosity and bacterial load than the thawed content used in Experiment 1, suggesting the importance of content integrity and freshness in infection effectiveness. These findings underscore the complexities of inducing H. meleagridis infections and highlight the need for ongoing research in this domain.