Feline calicivirus (FCV), first discovered and identified by scientists in the early 1950s, has attracted widespread attention due to its distinctive cup-shaped morphology and its impact on feline species (Fumian et al., 2018). Researchers have classified FCV within the caliciviridae family, and its unique genomic structure and protein composition result in diverse pathological effects within the feline body. The transmission of FCV primarily occurs through airborne particles and direct contact. Once a cat within a group is infected, the virus can spread rapidly to other cats through sneezing, coughing, or direct contact. This highly contagious characteristic makes the spread of FCV extremely rapid in cat herds, posing a potential threat to the health of feline populations (Spiri et al., 2019; Wang and Lin, 2024).

FCV infection is a common occurrence in cat populations worldwide. Both domestic and stray cats may be infected with FCV. This high prevalence makes FCV a significant factor requiring attention in feline population health management (Liu et al., 2022). The disease symptoms caused by FCV are varied, including upper respiratory tract infections and oral ulcers. Current research primarily focuses on the basic biological characteristics of FCV, its transmission pathways, and the pathological manifestations during the acute infection stage. However, there is still a knowledge gap in understanding the long-term effects of chronic FCV infection and its dynamics in feline populations, necessitating a deeper understanding of FCV's long-term impact on feline health during chronic infection.

The purpose of this study is to comprehensively understand the transmission dynamics of FCV in cat populations and explore the potential impact of chronic FCV infection on feline health. By gaining a thorough understanding of FCV, this research aims to provide insights for future disease management and prevention strategies, serving as a scientific basis for reducing the spread of FCV in feline populations and treating chronic infections. This study is crucial for improving feline population health and ensuring the safety of close interactions between humans and cats.

1 Basic Knowledge of FCV

Feline calicivirus (FCV), a member of the caliciviridae family, possesses a unique viral structure that profoundly influences its infection process and pathological effects (Zhou et al., 2023). The virus particles of FCV exhibit a cup-like shape, distinguishing it from others. The outer layer of the virus is enveloped in a membrane covered with crown-like projections, containing crucial proteins that determine the interaction between the virus and host cells. Additionally, the genome of FCV is a positive-sense RNA, encoding various proteins, including key enzymes and structural proteins directly involved in virus replication and assembly (Wang, 2023).

FCV's host range encompasses feline species, with domestic cats being the primary hosts. This broad host adaptability is a significant factor in the spread of FCV within cat populations. The virus is transmitted through airborne droplets and direct contact, yet the adaptability and transmission mechanisms in different hosts remain crucial research focuses. In parasitic biology, FCV replicates and releases within host cells, forming latent infections within host animals. Understanding this parasitology is essential for the treatment and management of FCV infections.

FCV exhibits high genetic variability, primarily reflected in the RNA sequences of its genome (Zheng et al., 2022). This variability results in the emergence of different viral strains, which may demonstrate varying transmission capabilities and pathogenicity. Understanding the genetic variability of FCV is crucial for developing effective vaccine and treatment strategies. Future research needs to delve deeper into how these variations affect the transmission and pathological characteristics of FCV to better address the challenges posed by different variant strains.

2 Transmission Dynamics of Feline Calicivirus (FCV) in Cat Populations

2.1 Transmission pathways

The transmission pathway of FCV is the basis for studying its transmission dynamics in cat herds. The main transmission pathways include:

FCV can spread through airborne aerosols, particularly in enclosed environments such as veterinary clinics and catteries. Droplet transmission is a major mode, where virus particles expelled during coughing or sneezing by infected cats can linger in the air, making other cats susceptible upon inhalation.

Direct contact is another significant pathway for FCV transmission. This involves close interactions between infected cats, such as kissing, grooming, sharing food and water, etc. (Bai et al., 2022). This form of transmission is common in cat populations, especially in environments where multiple cats live together.

FCV can be transmitted through environmental surfaces, especially in areas where the virus is released, such as locations where infected cats cough or sneeze. Virus particles may persist on surfaces for some time, and other cats may become infected by coming into contact with these contaminated surfaces.

2.2 Seasonal and geographic variations in transmission dynamics

The transmission of FCV may vary across different seasons. Some studies suggest that cold and humid seasons may facilitate the spread of FCV within cat populations. This could be related to seasonal changes in the immune system, cat behavior patterns, and the stability of the virus in different environments.

Transmission dynamics of FCV may also exhibit variations in different geographic regions. This could be influenced by factors such as climate conditions, cat population density, and veterinary hygiene practices. Investigating geographic differences contributes to a better understanding and prediction of FCV transmission dynamics in different regions, providing a scientific basis for the development of corresponding prevention and control strategies.

3 Impact of Chronic FCV Infection

3.1 Clinical manifestations

Chronic FCV infection has widespread and complex effects on the health of cats. This study delves into the clinical manifestations of chronic infection, including symptoms of acute infection and the manifestations of chronic infection. Acute symptoms of FCV infection typically include flu-like symptoms such as fever, coughing, sneezing, and conjunctivitis. These symptoms may be mild in the early stages of infection but can progress to severe respiratory symptoms like rapid breathing and increased nasal discharge. Chronic FCV infection presents more complex manifestations. Cats may experience recurrent respiratory infections with symptoms such as sneezing, nasal discharge, and flu-like symptoms (Wang and Lin, 2024). Additionally, chronic infection may lead to oral ulcers, conjunctivitis, and other manifestations (Figure 1), impacting the quality of life for the cat.

3.2 Interaction with other feline viruses

The interaction between FCV and other feline viruses may have profound effects on the health of cats during the course of chronic infection. Interaction between FCV and feline coronavirus could lead to more complex symptoms in cats. Studies suggest that the coexistence of these two viruses may increase the risk of chronic infection and may also trigger conditions such as feline infectious peritonitis. FCV infection could exacerbate the course of feline immunodeficiency virus (FIV) infection, compromising the immune system of affected cats. This interaction may result in more severe and challenging-to-treat infections.

3.3 Potential consequences of FCV infection

Chronic FCV infection may have long-term effects on the cat's immune system, making it more susceptible to infections by other pathogens (Peñaflor-Téllez et al., 2019). This increased susceptibility may lead to a higher likelihood of contracting other diseases throughout the cat's lifespan, making treatment more challenging. Chronic FCV infection could also have enduring effects on other systems, such as the respiratory and oral systems. This could expose the cat to various health issues over the long term, necessitating comprehensive management strategies.

3.4 Clinical case analysis

Through an in-depth analysis of FCV infection cases in kittens and adult cats, this study reveals significant differences in the manifestations of FCV infection across different age groups. Some kittens infected with FCV may exhibit acute respiratory symptoms, such as frequent sneezing, conjunctivitis, and even a decrease in appetite. These symptoms could adversely affect the growth and development of kittens, necessitating timely intervention and treatment. In contrast, adult cats may present more complex manifestations after FCV infection. Apart from respiratory symptoms, some adult cats may experience abnormal immune responses, such as oral ulcers and conjunctivitis. This complexity in manifestations requires a comprehensive approach, considering both immune modulation and antiviral treatment (Wang and Lin, 2024).

Chronic FCV infection may trigger potential disease developments, with markedly different characteristics at different stages of the disease. Some cats, after prolonged FCV infection, may develop respiratory complications like chronic airway diseases. This requires continuous monitoring and treatment to prevent further deterioration. Chronic infection may lead to the formation of oral ulcers, affecting the cat's feeding habits. This not only impacts the cat's nutritional intake but may also result in other related issues, such as weight loss and further compromise of the immune system.

Different living conditions and environmental factors within cat populations may influence the clinical manifestations of FCV infection (Tao et al., 2023). Domesticated cats, receiving regular veterinary check-ups and vaccinations, may exhibit milder symptoms of FCV infection. Conversely, in stray cat populations living in relatively harsh environments, FCV infection may be more prevalent and present more severe symptoms. In households with multiple cats, the transmission of FCV may be rapid, posing a risk of mutual infection among family members. Managing FCV infection in such environments becomes more complex and requires targeted measures.

4 Disease Management and Prevention Strategies

4.1 Current treatment approaches

Currently, antiviral drugs play a crucial role in the treatment of FCV infection (Tian et al., 2020). Some drugs, such as antiviral nucleoside analogs, have been widely used and have achieved success in alleviating acute infection symptoms. However, addressing the long-term efficacy against chronic infections remains a pressing issue.

In addition to antiviral drugs, symptomatic treatment is also an essential means of managing FCV infections. For instance, maintaining fluid balance through oral or injectable fluids and employing supportive therapies to alleviate respiratory symptoms in cats. These treatment methods can provide effective support during the acute infection period.

4.2 Vaccine development and application

Existing FCV vaccines have shown some effectiveness in preventing infection and reducing symptoms (Wang, 2023). However, challenges arise due to the existence of viral variants that exhibit resistance to traditional vaccines. Therefore, evaluating the effectiveness of existing vaccines and considering modifications to enhance their broad-spectrum coverage is a crucial direction in current research.

With the continuous advancement of vaccine technology, the development of the next generation of FCV vaccines is underway. These vaccines may be more broad-spectrum, covering a greater range of variants, and providing more durable immune protection. Future research will focus on the safety and efficacy of these novel vaccines.

4.3 Future research directions

Future vaccine research will emphasize the development of more innovative and efficient FCV vaccines. This may involve using new vaccine vectors, modifying vaccine components, and utilizing genetic engineering techniques to design more intelligent vaccines. These efforts are expected to offer comprehensive immune protection and alleviate the impact of FCV infection on cat populations.

Understanding the molecular mechanisms of chronic FCV infection is crucial for developing more precise treatment methods (Zhou et al., 2021). Future research will delve into the virus's lifecycle within host cells, seeking new targets for treating chronic infections. In-depth exploration in this field holds the potential to provide new breakthroughs in treating chronic FCV infections.

5 Conclusion

FCV, as a common cat virus, is crucially important to understand comprehensively for the development of effective treatment and prevention strategies. In-depth research into the virology, transmission dynamics, and the impact of chronic infections of FCV provides researchers with a more comprehensive understanding of the characteristics and behavior of this virus. From viral structure to host range, transmission pathways to potential consequences, this information lays the foundation for developing comprehensive management plans.

At the clinical level, this study delves into the clinical manifestations of FCV infection, the characteristics of chronic infections, and the interactions with other cat viruses. Through clinical case analysis, researchers can gain clearer insights into the varied responses of cats to FCV infection across different age groups and populations. This aids in enhancing the level of targeted treatment by clinical doctors and veterinarians, ensuring the health of cat populations more effectively.

With the continuous advancement of scientific technology, future research on FCV will focus on several key directions: Virological progress: Further understanding the genetic variations, lifecycle, and virus replication mechanisms of FCV can contribute to the discovery of new therapeutic targets (Bordicchia et al., 2021). Vaccine development: The development of next-generation vaccines will be a critical focus, aiming to enhance the breadth and duration of vaccine efficacy to counteract viral mutations. Mechanisms of chronic infection: In-depth exploration of the molecular mechanisms of chronic FCV infection to find more effective treatment methods, possibly involving emerging fields like gene therapy. Epidemiological research: Strengthening global epidemiological monitoring of FCV to understand the seasonal and geographical variations in transmission dynamics, providing data support for precise prevention and control.

By combining these future research directions, researchers can hope to further expand their understanding of FCV, improve treatment effectiveness, alleviate the impact of chronic infections, and ultimately achieve better management of this virus. In this process, interdisciplinary collaboration and technological innovation will be crucial driving forces for advancing research. Collective efforts instill confidence in overcoming FCV in the future, protecting beloved cats from its disturbances.

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