What causes infectious diseases?

Experts Explain What Causes Infectious Diseases

Infectious diseases are caused by biological agents that invade the body and disrupt normal function, experts said. Scientists identify primary causes as bacteria, viruses, fungi, parasites and, in rare cases, prions. Transmission occurs through multiple routes: direct contact, respiratory droplets and airborne spread, contaminated food or water, vector-borne transmission via insects, and contaminated surfaces. Health authorities note that host factors such as age, immune status, chronic conditions and malnutrition influence susceptibility. Environmental conditions — including overcrowding, poor sanitation and climate variables — also shape spread, specialists added.

Public health leaders emphasize zoonotic spillover when pathogens move from animals to humans; HIV, influenza and several coronaviruses originated this way. Antimicrobial resistance has emerged as a major driver of persistent infections, reducing the effectiveness of antibiotics and antiviral drugs, clinicians warned. Social determinants — access to healthcare, vaccination coverage, and socioeconomic disparities — further modulate disease burden.

"Preventing infection requires addressing pathogens, transmission pathways and societal factors," said Dr. Maria Santos, an infectious disease epidemiologist at Johns Hopkins University, citing surveillance, vaccination, sanitation and prudent antimicrobial use as core measures. Clinical teams use diagnostic testing and targeted therapy to control outbreaks, while researchers study pathogen genetics to inform vaccines and treatments.

The Centers for Disease Control and Prevention and global health agencies provide guidance on containment strategies and risk communication. Understanding causation, specialists conclude, demands integrated approaches that combine laboratory science, clinical practice and public health policy to reduce transmission and protect vulnerable populations.

Recent peer-reviewed studies reinforce this evidence, showing environmental control, vaccination and early detection lower rates significantly. Public health officials urge communities to support surveillance networks and invest in laboratory capacity so clinicians can rapidly diagnose and treat infections. Coordinated action, experts say, remains essential to limit emergence and spread of infectious diseases worldwide today.