Measles is a highly contagious disease primarily recognized for its widespread impact on human populations. It is characterized by fever, cough, runny nose, and a distinctive rash, and spreads easily. Its history and connections to the animal kingdom reveal a fascinating journey, prompting questions about whether animals can contract this human-specific virus or related pathogens.
Is Measles a Human-Specific Disease?
The human measles virus (MeV) is a human-to-human pathogen, primarily infecting and spreading among people. The Centers for Disease Control and Prevention (CDC) confirms measles is a human disease, not transmitted from or by animals. This specificity arises because the virus targets human cells, utilizing particular receptors on human cell surfaces.
While household pets like dogs and cats cannot naturally contract or transmit human measles, some non-human primates, such as apes and certain monkeys, are susceptible to MeV infection. These cases are observed in controlled environments or as outbreaks within captive populations, often linked to contact with infected human personnel. Wild non-human primate populations are not large enough to sustain endemic measles circulation, meaning natural, ongoing infection in these animals is not common.
The Ancestral Link to Animals
Despite measles being a human-specific disease today, scientific understanding points to its origins in the animal kingdom. The human measles virus evolved from the rinderpest virus (RPV), a morbillivirus that caused severe disease in cattle and other cloven-hoofed animals. This evolutionary jump from animals to humans is known as a zoonotic spillover event.
Genetic analysis suggests the measles virus diverged from its rinderpest ancestor much earlier than previously thought, potentially between 1174 BCE and 165 CE, with a mean estimate around 528 BCE. This timeline coincides with the rise of large urban centers, which provided the dense human populations necessary for the virus to establish and sustain itself. Rinderpest, often called “cattle plague,” caused high mortality rates, sometimes reaching 100% in susceptible herds. Its global eradication in 2011, achieved through vaccination and surveillance, made it only the second infectious disease, after smallpox, to be wiped out globally.
Other Measles-Like Viruses in Animals
Beyond the direct ancestral link to rinderpest, several other morbilliviruses share a genetic relationship with the human measles virus. These viruses, distinct from MeV, can cause similar disease symptoms in their respective hosts. For instance, Canine Distemper Virus (CDV) infects a wide range of carnivores, including domestic dogs, ferrets, foxes, and wolves.
Peste des Petits Ruminants Virus (PPRV) causes a highly contagious disease in sheep and goats, sometimes called “sheep and goat plague.” Marine mammals are also susceptible to morbilliviruses, with specific strains like Phocine Distemper Virus (PDV) affecting seals and Cetacean Morbillivirus (CeMV) affecting dolphins, porpoises, and whales. While these animal morbilliviruses are genetically related to measles and can cause severe illness in their hosts, they do not transmit to humans, underscoring the species-specific nature of most morbillivirus infections.