EXPERIMENTAL STUDIES ON YELLOW FEVER OCCURRING IN MERIDA, YUCATAN

Area of Science:

• * Infectious Diseases
• * Veterinary Medicine
• * Microbiology

Background:

• * Yellow fever is a severe viral hemorrhagic fever with significant public health implications.
• * Understanding transmission dynamics and causative agents is crucial for disease control.
• * Previous research faced challenges in isolating and culturing the pathogen.

Purpose of the Study:

• * To investigate the transmissibility of yellow fever from human cases to animal models.
• * To identify the causative agent of yellow fever through experimental transmission and direct visualization.
• * To establish a reliable animal model for studying yellow fever pathogenesis and potential treatments.

Main Methods:

• * Inoculation of guinea pigs with blood and organ emulsions from fatal yellow fever cases.
• * Monitoring of animals for clinical signs, including fever and hemorrhagic lesions.
• * Subsequent transmission experiments to confirm infectivity and passage of the agent.
• * Microscopic examination (dark-field) for the presence of leptospires in primary samples and infected animals.

Main Results:

• * Experimental transmission of yellow fever to guinea pigs resulted in febrile reactions and characteristic visceral lesions, including hemorrhages.
• * Successful serial passage of the infectious agent in guinea pigs was achieved, confirming its viability and pathogenicity.
• * Leptospira were identified in primary cultures and in experimentally infected guinea pigs from Case 2, but not consistently from Case 1.
• * The agent from Case 2 demonstrated successful transmission via blood cultures, with optimal infectivity observed from early-stage blood samples.

Conclusions:

• * Guinea pigs serve as a viable animal model for studying yellow fever, exhibiting key pathological features.
• * The study provides strong evidence for the role of leptospires in the observed yellow fever cases, particularly Case 2.
• * Successful experimental transmission highlights the potential for direct and indirect routes of infection and underscores the importance of early diagnosis and intervention.