In late July, France’s National Public Health Agency released an initial report on enhanced arboviral surveillance that documented the first locally acquired cases of chikungunya, dengue, and West Nile virus infection in 2026. These cases come on top of a sharp rise in imported infections since the start of the year, raising concern that imported cases could seed additional local transmission. The report underscores the need for clinicians to promptly recognize the clinical signs, make a diagnosis, and immediately notify public health authorities. It also highlights the importance of being able to distinguish these infections from other conditions in the differential diagnosis.

Is It an Arbovirus Infection?

Chikungunya, dengue, and Zika are three arboviral infections spread by the Asian tiger mosquito (Aedes albopictus), which is now established in nearly all of mainland France, across 83 departments. West Nile virus, by contrast, is transmitted by Culex mosquitoes.

After an incubation period of about 2-10 days, these infections are often asymptomatic. When symptoms do occur, they typically begin abruptly with a flu-like syndrome, including fever, muscle aches and/or joint pain, headaches, a skin rash, and fatigue (see Table).

Diagnosis is confirmed by RT-PCR during the first 5 days after symptom onset and through day 7. Serologic testing, with immunoglobulin G followed by immunoglobulin M, may be used as an alternative between days 5 and 7, and is the only valid option beginning on day 10.

When faced with a patient presenting with flu-like symptoms, France’s National Public Health Agency recommends:

• Inquire about a recent trip to a geographic area where viral circulation has been reported. 
• Assess the time interval between exposure and symptom onset to distinguish between imported and autochthonous cases. 
• Do not overlook trips to a French department where the Aedes albopictus is established for the viruses in question. 

Specific Signs of the Dengue Virus

The clinical signs most often appear between 4 and 7 days after the bite but can take up to 2 weeks. In addition to flu-like symptoms including high fever, widespread aches and pains, severe fatigue, diffuse headache, retroorbital pain, nausea, vomiting, and a skin rash, thrombocytopenia is a key laboratory finding that may suggest the diagnosis. About a week after symptom onset, patients may also develop cutaneous findings such as a maculopapular rash, purpura, and pruritus, along with bradycardia. Asthenia can linger for several weeks after the initial presentation.

In approximately 5% of cases, the disease is severe and can be life-threatening. Individuals at risk include those who have previously been infected with a serotype other than the current one, as well as children younger than 2 years, the older adults, women in the third trimester of pregnancy, and people with chronic diseases or sickle cell disease. Warning signs of a sudden onset include symptoms of encephalopathy, rhabdomyolysis, hepatitis, cholecystitis, or encephalitis. As the disease progresses, shock accompanied by abdominal pain, persistent vomiting, impaired consciousness, or hemorrhagic complications may develop.

Specific Signs of the Chikungunya Virus

After an incubation period of 3-7 days, chikungunya almost always causes fever during the first 3 days, headaches, severe muscle pain, conjunctivitis, as well as bilateral, symmetrical, and highly debilitating joint symptoms (arthralgia and arthritis). Affection of the hands and feet, as well as periarticular edema, are common. The presence of tenosynovitis in the wrists and ankles is highly suggestive of the disease.

There is also often a diffuse exanthem or a pruritic maculopapular rash, particularly on the trunk and arms, and lymphadenopathy, particularly in the cervical region.

Some patients may develop a severe form with neurologic involvement and a risk for meningoencephalitis, as well as peripheral nerve involvement. These severe forms primarily affect children infected in utero, as well as the older or immunocompromised individuals. The condition is rarely life-threatening and is more commonly linked to an associated chronic condition that worsens during the acute episode. There is a risk that joint manifestations may become chronic.

Specific Signs of West Nile virus

In addition to flu-like symptoms, the West Nile virus can cause severe, potentially fatal neurologic complications: meningitis, meningoencephalitis, polyradiculoneuritis, flaccid paralysis, or Guillain-Barré syndrome, associated with clear cerebrospinal fluid. Those at risk for severe disease include adults, the older adults, and immunocompromised individuals. Diagnosis relies on RT-PCR, and serology is only useful after the 8th day following symptom onset.

Specific Signs of Zika Virus

When symptomatic, the infection generally presents as a moderate flu-like syndrome with a low-grade fever or no fever at all, a pruritic maculopapular rash that most often appears first on the face, accompanied by nonpurulent conjunctivitis and other mild or absent symptoms (joint pain, muscle pain, and headache). In rare cases, there is a risk for Guillain-Barré syndrome.

Zika poses a risk for congenital malformations in pregnant women, primarily during the first trimester of pregnancy: In cases of mother-to-fetus transmission, cases of microcephaly, intracranial calcifications, and ocular and/or neurologic abnormalities have been reported.

Table. Signs and Symptoms of Arbovirus Infections

This story was translated from Univadis France, part of the Medscape Professional Network.