Why don't humans get canine plague, what immunity do they have? - briefly
Humans generally do not contract canine plague, also known as canine distemper, primarily because the virus that causes it is highly species-specific. This specificity means that the virus is adapted to infect dogs and other canines, and it does not readily infect humans.
The immunity in humans to canine plague can be attributed to several factors:
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Species Barrier: The canine distemper virus (CDV) has a strong preference for specific receptors found on the cells of canines. Humans lack these receptors, making it difficult for the virus to infect human cells.
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Immune System Response: Even if the virus were to enter a human body, the human immune system is equipped to recognize and combat it as a foreign invader. This robust immune response helps in preventing the virus from establishing an infection.
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Vaccination and Past Exposure: While not directly related to canine distemper, humans often have antibodies from vaccinations against related viruses, such as measles. These antibodies can provide some level of cross-protection against CDV.
In summary, the combination of species-specific virus adaptation and a strong human immune system makes it rare for humans to contract canine plague.
Why don't humans get canine plague, what immunity do they have? - in detail
Canine plague, also known as canine distemper, is a highly contagious viral disease that affects dogs and other animals such as ferrets, raccoons, and big cats. Humans, however, are not susceptible to this disease due to several biological and immunological factors. Understanding these factors provides insight into the mechanisms of species-specific immunity.
The canine distemper virus (CDV) is a paramyxovirus, closely related to the measles virus in humans. Despite this genetic similarity, the virus has evolved to specifically target canine species and their close relatives. The primary reason humans do not contract canine distemper is the lack of specific receptors on human cells that the CDV requires to enter and infect them. The virus binds to a protein called signaling lymphocyte activation molecule (SLAM) on the surface of immune cells. In dogs, SLAM is expressed on various immune cells, facilitating viral entry. In humans, the SLAM protein is not present on the same types of cells, making it difficult for the virus to gain entry into human cells.
Additionally, humans have developed a robust immune response to related viruses, such as measles. The immune system in humans has evolved to recognize and neutralize viruses that are similar to CDV. This cross-reactivity provides a form of indirect immunity. Vaccination against measles in humans further enhances this immunity, as the measles vaccine stimulates the production of antibodies that can also neutralize CDV to some extent. This cross-protection is a result of the shared antigenic properties between measles and canine distemper viruses.
The human immune system is also equipped with a variety of defense mechanisms that can recognize and eliminate foreign pathogens. Natural killer cells, macrophages, and other components of the innate immune system can detect and destroy infected cells before the virus can establish a significant infection. Moreover, the adaptive immune system, which includes T cells and B cells, can mount a specific response against the virus if it were to encounter it, although this is rarely necessary due to the lack of receptor compatibility.
In summary, the primary reasons humans do not contract canine distemper include the absence of specific receptors on human cells, the presence of cross-reactive immunity from related viruses, and the robust defense mechanisms of the human immune system. These factors collectively ensure that humans remain resistant to this canine-specific disease.