Arboviruses (arthropod-borne viruses) are a group of viruses that are transmitted to humans and other animals primarily through the bites of infected arthropods, such as mosquitoes, ticks, and sandflies. These viruses can cause a range of diseases, from mild febrile illnesses to severe diseases like encephalitis, hemorrhagic fever, or systemic infection. Arboviruses are important in public health due to their ability to cause outbreaks, often with severe consequences.
A. Veterinary Arboviruses
- West Nile Virus (WNV)
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Birds (amplifying hosts), horses, humans
- Transmission: Primarily through mosquito bites (Culex spp.).
- Pathogenesis: Virus enters the bloodstream, can cross the blood-brain barrier, leading to encephalitis in susceptible hosts.
- Clinical Signs: Fever, depression, ataxia, seizures, neurological signs in horses (e.g., weakness, inability to stand).
- Prevention: Vaccination for horses, mosquito control, and reducing standing water.
- Eastern Equine Encephalitis (EEE)
- Family: Togaviridae
- Genus: Alphavirus
- Host: Horses, birds, humans
- Transmission: Mosquito bites (primarily Aedes and Culiseta spp.).
- Pathogenesis: Infection leads to neurological disease; the virus can cause inflammation in the brain.
- Clinical Signs: Fever, depression, neurological signs (e.g., seizures, ataxia, disorientation).
- Prevention: Vaccination for horses, mosquito control, and avoiding exposure to mosquitoes.
- Western Equine Encephalitis (WEE)
- Family: Togaviridae
- Genus: Alphavirus
- Host: Horses, birds, humans
- Transmission: Mosquito bites (primarily Culex spp.).
- Pathogenesis: Similar to EEE, leading to encephalitis and severe neurological disease.
- Clinical Signs: Fever, neurological signs (e.g., lethargy, circling, inability to stand).
- Prevention: Vaccination for horses, mosquito control, and reducing exposure to mosquitoes.
- Bovine Viral Diarrhea Virus (BVDV)
- Family: Flaviviridae
- Genus: Pestivirus
- Host: Cattle (cows, bulls, calves)
- Transmission: Direct contact, bodily fluids, and possibly via biting insects (though not primarily arboviruses).
- Pathogenesis: Causes immunosuppression and can lead to reproductive issues and gastrointestinal disease.
- Clinical Signs: Diarrhea, respiratory illness, reproductive issues (abortions, stillbirths).
- Prevention: Vaccination, biosecurity measures.
- Zika Virus
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Primates (including humans), mosquitoes (amplifying host)
- Transmission: Mosquito bites (primarily Aedes aegypti), sexual contact, vertical transmission (from mother to fetus).
- Pathogenesis: Infection can lead to neurological disorders in fetuses (e.g., microcephaly).
- Clinical Signs: Mild fever, rash, conjunctivitis, joint pain; severe cases may lead to neurological issues.
- Prevention: Mosquito control, avoiding mosquito bites, and public health awareness.
B. Medical Arboviruses
- Dengue Virus
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Humans, primates
- Transmission: Mosquito bites (primarily Aedes aegypti and Aedes albopictus).
- Pathogenesis: The virus can replicate in various cell types, leading to a range of symptoms from mild to severe dengue fever.
- Clinical Signs: High fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and in severe cases, bleeding and shock (Dengue Hemorrhagic Fever).
- Prevention: Mosquito control, vaccination (Dengvaxia), personal protection against bites.
- Chikungunya Virus
- Family: Togaviridae
- Genus: Alphavirus
- Host: Humans, monkeys
- Transmission: Mosquito bites (primarily Aedes aegypti and Aedes albopictus).
- Pathogenesis: The virus infects fibroblasts and endothelial cells, causing inflammation.
- Clinical Signs: Sudden onset of fever, severe joint pain, muscle pain, headache, and rash.
- Prevention: Mosquito control, personal protection against bites.
- Yellow Fever Virus
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Humans, monkeys
- Transmission: Mosquito bites (primarily Aedes aegypti).
- Pathogenesis: Virus replication in the liver can lead to severe liver damage and hemorrhagic symptoms.
- Clinical Signs: Fever, chills, loss of appetite, muscle pain, and in severe cases, liver damage leading to jaundice and hemorrhage.
- Prevention: Vaccination (highly effective), mosquito control.
- Japanese Encephalitis Virus (JEV)
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Birds (reservoir), pigs, humans
- Transmission: Mosquito bites (primarily Culex tritaeniorhynchus).
- Pathogenesis: Infection leads to encephalitis, especially in children.
- Clinical Signs: Fever, headache, vomiting, neurological symptoms (e.g., seizures, confusion).
- Prevention: Vaccination, mosquito control measures.
- Tick-borne Encephalitis Virus (TBEV)
- Family: Flaviviridae
- Genus: Flavivirus
- Host: Humans, rodents, large mammals
- Transmission: Tick bites (primarily Ixodes ricinus).
- Pathogenesis: The virus can infect the central nervous system, leading to inflammation.
- Clinical Signs: Fever, headache, fatigue, neurological symptoms (e.g., meningitis, encephalitis).
- Prevention: Vaccination, avoiding tick-infested areas, and protective clothing.
Characteristics
- Transmission cycle: Arboviruses generally require a vector (usually a blood-feeding arthropod) to move between vertebrate hosts. The virus replicates in the vector before being transmitted to a new host.
- Hosts: Typically have a primary (reservoir) host in which the virus circulates without causing significant disease (such as birds or small mammals). Humans are often incidental hosts.
- Geographical distribution: Most arboviruses are geographically restricted based on the distribution of their vector (e.g., tropical regions for Aedes mosquitoes).
Disease Prevention and Control
- Vector control: Reducing mosquito populations through the use of insecticides, eliminating breeding sites, and introducing biological controls.
- Vaccination: Some arboviruses have vaccines (e.g., Yellow Fever, Japanese Encephalitis), but many, like Dengue or Zika, do not.
- Personal protection: Use of insect repellents, bed nets, and protective clothing to avoid vector bites.
Arboviruses have become more relevant due to global warming, which is expanding the range of vectors, and increasing international travel, which facilitates the spread of these viruses to new regions.