Image: This transmission electron photomicrograph shows a negative-stained, Fortaleza-strain Zika virus (red) (Photo courtesy of the US National Institutes of Health).
Zika virus disease is caused by a virus transmitted primarily by Aedes mosquitoes. People with Zika virus disease can have symptoms including mild fever, skin rash, conjunctivitis, muscle and joint pain, malaise or headache.
Zika virus, belonging to the family Flaviviridae and genus Flavivirus, is transmitted to humans by mosquito bites but can also be contracted through sexual and vertical transmission. As with other arboviruses, Zika virus viremia is commonly measured in venous blood, even though mosquitoes introduce virus into cutaneous capillary blood.
A team of scientists working with those at the Institut Pasteur de la Guyane (Cayenne, French Guiana) collected venous and capillary serum samples from 21 Zika virus‒infected patients on multiple days after symptom onset. They confirmed Zika virus infection by real-time reverse transcription polymerase chain reaction (RT-PCR) of serum and urine samples provided by patients during the first few days after symptom onset.
The team obtained serum samples from the venous and cutaneous capillary blood (collected from the fingertip) sequentially 1 to 18 days after the onset of symptoms. The median age of the population was 40 (range 28–63) years and the sex ratio, male:female was 1.6. They extracted RNA from 150-µL samples using the QIAamp Viral RNA kit and performed Zika virus RNA amplification using the RealStar Zika Virus RT-PCR Kit. They performed Zika virus RNA quantification using a reference strain and estimated the Zika virus RNA load as log10 copies/mL.
The scientists found that Zika virus RNA loads in capillary blood correlated with those in venous blood but were significantly higher in the capillary samples, except for three patients. The median duration of Zika virus detection after symptom onset was significantly greater in capillary blood than in venous blood, even though the duration of detection in capillary blood was underestimated; RNA was still detectable in the last capillary blood samples taken from eight patients. The duration of Zika virus RNA detection was greater in capillary than in venous blood for 12 of the 21 patients. The maximum duration of RNA detection in capillary blood samples was 18 days after the onset of symptoms with a load of 1.9 log10 copies/mL.
The authors concluded that if the Zika virus RNA observed in the serum samples taken from the capillary compartment reflects the presence of infectious virus particles, symptomatic Zika virus‒infected patients would need to be shielded from mosquitoes for a longer period than is currently practiced to limit potential vector-borne transmission. The study was published in the November 2017 edition of the journal Emerging Infectious Diseases.
Institut Pasteur de la Guyane