Arboviruses are viruses transmitted to humans and other vertebrates through the bites of infected arthropods. They are a global public health concern, causing illness, sometimes severe. The term “arbovirus” encompasses over 500 recognized viruses, with 80 known to cause human disease. Present on all continents except Antarctica, they pose a continuous global challenge.
The Arbovirus Transmission Cycle
Arbovirus transmission relies on a cycle involving arthropod vectors and vertebrate hosts. Blood-feeding arthropods like mosquitoes and ticks acquire the virus when feeding on an infected animal. Once ingested, the virus replicates within the vector’s tissues, including the midgut and salivary glands, over several days to weeks, making the vector infectious.
Once infectious, the arthropod can transmit the virus to a new host through a subsequent bite. The vector injects viral particles into the host’s bloodstream or skin during a bite. Vertebrate hosts, such as birds, rodents, or primates, serve as natural reservoirs where the virus circulates without causing severe disease. They maintain the virus in nature, continuing the cycle.
Humans frequently act as “dead-end hosts” for many arboviruses, as they typically don’t develop enough virus in their blood (viremia) to infect another biting arthropod. This limits human-to-vector transmission. However, certain arboviruses, like Dengue or Zika, can establish an urban cycle where humans develop sufficient viremia to act as amplifying hosts, allowing mosquito transmission between people. This can lead to widespread outbreaks in densely populated areas.
Common Arboviral Diseases
Among the many arboviruses, several are particularly well-known for their impact on human health, each presenting with distinct symptom profiles. Dengue, caused by the dengue virus, is widespread in tropical and subtropical regions. Symptoms often include a sudden high fever, severe headache, pain behind the eyes, muscle and joint pain, and a rash. In some cases, dengue can progress to severe dengue, characterized by plasma leakage, severe bleeding, or organ impairment.
West Nile Virus (WNV) is found across Africa, Europe, Asia, and North America. Most WNV infections are asymptomatic, but 20% of infected individuals develop West Nile fever, with symptoms like fever, headache, body aches, joint pain, vomiting, diarrhea, or rash. Less than 1% may develop severe neuroinvasive disease, including encephalitis or meningitis, with high fever, neck stiffness, disorientation, tremors, convulsions, or paralysis.
Zika virus, identified in Uganda, has expanded globally, with outbreaks in the Americas. While many Zika infections are asymptomatic, symptomatic individuals may experience fever, rash, conjunctivitis (red eyes), muscle and joint pain, and headache. Zika infection during pregnancy is a concern due to its association with microcephaly and other congenital anomalies in newborns. The virus has also been linked to Guillain-Barré syndrome in adults.
Chikungunya virus causes sudden fever and severe joint pain, often affecting multiple joints simultaneously. Other symptoms include muscle pain, headache, nausea, fatigue, and a rash. The joint pain can be debilitating and may persist for weeks, months, or even years after the initial infection, impacting quality of life. This disease is prevalent in parts of Africa, Asia, and has spread to the Americas.
Diagnosis and Treatment Approaches
Diagnosing arboviral infections involves laboratory tests detecting viral components or immune response. Initial diagnosis uses molecular tests like RT-PCR, identifying viral RNA from blood, cerebrospinal fluid, or tissue samples. These are effective early when the virus circulates at high levels. As infection progresses, antibody tests (serological assays) detect specific antibodies (IgM and IgG), indicating recent or past infection.
Most arboviral diseases lack specific antiviral medication. Treatment is supportive, alleviating symptoms and aiding recovery. This involves rest, hydration, and managing fever and pain with over-the-counter medications like acetaminophen. In severe cases, especially for neuroinvasive diseases like encephalitis, hospitalization may be needed for intravenous fluids, pain management, and supportive care.
While antiviral treatments are largely absent, vaccines have been developed for a few arboviral diseases for prevention. A Yellow Fever vaccine has long been available, providing long-lasting immunity. A dengue vaccine is also available in some regions for those with prior dengue infection, and research continues for other arbovirus vaccines to enhance global health security. These tools help mitigate the impact of these infections.
Prevention and Global Risk Factors
Preventing arboviral infections involves personal protection and environmental management. Individuals reduce risk by minimizing exposure to arthropod vectors. This includes using insect repellents (DEET, picaridin, or oil of lemon eucalyptus) on exposed skin and clothing. Wearing long-sleeved shirts and long pants, especially during peak vector activity, provides a physical barrier.
Securing homes with intact window and door screens prevents vectors from entering homes. Eliminating standing water around homes, like flower pots, old tires, or clogged gutters, removes mosquito breeding sites. These actions lower local vector populations and reduce transmission.
Global risk factors expand arboviral outbreaks. Climate change contributes to warmer temperatures and altered rainfall, extending the range and breeding seasons of arthropod vectors like mosquitoes and ticks. This makes new areas suitable for vector populations and arbovirus transmission. Urbanization also creates environments with inadequate sanitation and standing water, fostering vector breeding and increasing human-vector contact.
International travel and trade accelerate arbovirus spread. Infected travelers can introduce viruses into new regions with competent vectors, initiating local transmission cycles. Goods movement can also transport vectors across borders, establishing new populations. These factors highlight the complex, evolving nature of global arboviral disease risk.