International Journal of Molecular Veterinary Research, 2024, Vol.14, No.5, 219-226 http://animalscipublisher.com/index.php/ijmvr 221 the bacterial load without completely eradicating the pathogen. This state of infection is often identified through laboratory tests rather than clinical observation, as the host does not exhibit the typical signs of illness (Rocha et al., 2018). 3.2 Prevalence and distribution of subclinical infections in felines Subclinical infections are common in felines, particularly in environments where multiple animals are housed together, such as breeding colonies or shelters. For instance, feline enteric coronavirus (FECV) is known to cause subclinical infections in cats, with many infected individuals showing no clinical signs despite the presence of the virus (Pearson et al., 2019). The prevalence of such infections can vary based on factors like geographic location, population density, and the presence of other diseases that may compromise the immune system (Priolo et al., 2019). 3.3 Common bacterial pathogens responsible for subclinical infections Several bacterial pathogens are known to cause subclinical infections in cats. For example, Leishmania infantum, although primarily a protozoan, can lead to subclinical infections in felines, especially in areas where canine leishmaniosis is endemic. In these cases, cats may harbor the pathogen without showing symptoms, but they can still mount an immune response detectable through laboratory assays (Priolo et al., 2019). Additionally, other pathogens such as cytomegalovirus (CMV) in non-feline models have been shown to persist subclinically, affecting immune responses and potentially influencing the host's susceptibility to other infections (Rocha et al., 2018). In summary, subclinical bacterial infections in cats are defined by the presence of bacteria without clinical symptoms, are prevalent in certain environments, and can be caused by various pathogens, including those that are typically associated with other species. These infections can influence the host's immune response and overall health. 4 Impact of Subclinical Infections on Immune Response Subclinical bacterial infections in cats, particularly those caused by Bartonella henselae, can significantly impact the feline immune system. These infections often go unnoticed due to the absence of overt clinical symptoms, yet they can lead to chronic immune activation and alterations in immune cell populations. 4.1 Changes in immune cell populations during subclinical infections Subclinical infections can lead to notable changes in immune cell populations in cats. For instance, a study on a cat with Bartonella henselae infection revealed a marked increase in intermediate and lymphoblastic lymphocytes, along with reactive macrophages, indicating an immune response despite the lack of severe clinical symptoms (Nivy et al., 2022). This suggests that even in the absence of overt disease, the immune system is actively responding to the presence of the pathogen. 4.2 Cytokine imbalances and chronic immune activation Chronic immune activation due to subclinical infections can result in cytokine imbalances. Bartonella henselae, for example, is known to manipulate host immune responses, potentially leading to prolonged immune activation (Figure 2) (Thibau et al., 2022). This persistent activation can cause an imbalance in cytokine production, which may contribute to the development of immune-mediated conditions such as hemolytic anemia, as observed in some infected cats (Nivy et al., 2022). The ongoing immune response, even in the absence of symptoms, highlights the pathogen's ability to evade complete immune clearance and maintain a state of chronic infection. 4.3 Case study: Bartonella henselae and its effects on feline immunity Bartonella henselae serves as a prime example of how subclinical infections can affect feline immunity. In a documented case, a cat with Bartonella henselae infection exhibited persistent fever and lymphadenopathy, alongside immune-mediated hemolytic anemia, despite being subclinical for a significant period (Nivy et al., 2022). This case underscores the pathogen's potential to cause significant immune dysregulation, even when the infection is not overtly symptomatic. The study also highlights the effectiveness of a combination treatment with
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