Final answer:
Zoonotic diseases like Ebola virus and swine flu are often more virulent because they can jump from animals, where they may be benign, to humans who have no immunity to them. Increased human activity like deforestation and intensive farming increases exposure and spread of these pathogens.
Step-by-step explanation:
Why Zoonotic Diseases Are Sometimes More Virulent
Zoonotic diseases such as hemorrhagic fever caused by the Ebola virus and the H1N1 swine flu can sometimes be more virulent in humans than diseases that solely affect human hosts. These diseases, which can transfer from animals to humans, may have evolved to inflict strong virulence in their natural animal hosts, where the pathogens often circulate in large populations.
When they jump to humans, the pathogens can cause severe illness because humans may not have the necessary immunity or defenses against them.
Factors such as deforestation and high-density livestock farming can exacerbate this issue by increasing contact between wildlife carrying pathogens and human populations, making transmission more likely and sometimes enhancing the virulence of such diseases.
Additionally, viruses like the avian influenza virus, including strains like H5N1, have garnered attention due to their capability to transmit from birds to humans, potentially causing devastating outbreaks due to a lack of human immunity to these novel pathogens.