38. Arboviruses – the causative agents of vector- associated infections. General characteristics and classification. Genus Rubivirus. Bunyaviridae – the causative agent of Crimean-Congo haemorrhagic fever.

I. Definition and General Characteristics

• Arboviruses = ARthropod-BOrne viruses – a group of viruses transmitted by blood-sucking arthropods such as mosquitoes, ticks, and sandflies.
• They do not form a taxonomic group, but include viruses from several different families:
• Flaviviridae
• Togaviridae
• Bunyaviridae
• Reoviridae
• Transmission cycle usually involves:

1. Arthropod vector (biological vector, not just mechanical)
2. Vertebrate host (often human, birds, monkeys, or rodents)

II. Common Features of Arboviruses

• RNA viruses (except African swine fever virus – a DNA arbovirus).
• Replicate in both arthropod vectors and vertebrate hosts.
• Seasonal in temperate regions (depends on vector activity).
• Major clinical syndromes:
• Fever with or without rash
• Hemorrhagic fever
• Encephalitis
• Arthritis-like symptoms (chikungunya)

IV. Pathogenesis and Syndromes

A. Hemorrhagic Fevers (Capillary leakage + bleeding)

• Dengue hemorrhagic fever, Yellow fever, CCHF, Rift Valley fever
• Mechanisms:
• Cytokine storm
• Endothelial damage
• Platelet destruction and vascular leakage

B. Encephalitic Arboviruses

• Japanese encephalitis, West Nile virus, Tick-borne encephalitis
• Invade CNS → cause neuronal destruction, inflammation
• Signs: altered mental status, seizures, coma

C. Arthralgic Illnesses

• Chikungunya virus, Zika virus
• Strong inflammatory response in joints and muscles
• Often mimics rheumatoid arthritis in chronic cases