Mosquito-borne viruses - Bone marrow and peripheral blood stem cell

Essential information

Definition/s

Mosquito-borne virus risk areas are shown in the Geographical Disease Risk Index which includes details of the specific viral risks present

The day that a donor leaves a risk area is defined as Day 0.

Includes
  • Chikungunya Virus, also known as CHIKV
  • Dengue Virus, also known as Dengue Fever
  • Yellow Fever, also known as YF
  • Zika Virus, also known as ZIKV, and Zika Virus Fever
Obligatory

Must not donate if:

  1. It is less than 4 months since the donor has been diagnosed with Chikungunya, Dengue, Yellow Fever, or Zika virus infection.

  2. It is less than 4 months since the donor was last in a mosquito-borne virus risk area and the donor has either had a history of symptoms suggestive of Chikungunya, Dengue, Yellow Fever or Zika virus infection whilst there or following their return to the UK.

  3. In other cases, it is 28 days or less since the donor was last in a mosquito-borne virus risk area.
Discretionary

All donors may be accepted 4 months after their return from an affected area or resolution of symptoms. If the donor has not had a diagnosis of a mosquito-borne virus, nor has symptoms suggestive of infection, they may be accepted once more than 28 days have passed since they were last in a risk area.

If donor clearance is being carried out at less than 28 days since the donor has returned to the UK, a risk assessment will be required as to whether to proceed or delay the donation so that there is a clear 28 days since return to the UK and the donor has remained well.

Supporting information

See if relevant
Additional information

When an allogeneic stem cell donor who has been asymptomatic has returned from a mosquito-borne virus risk area, the preferred option is to wait for 28 days from return before clearing the donor if the stem cell collection can be delayed.

In exceptional circumstances, and if there is a pressing clinical need to proceed to clearing the donor or collection within 28 days of return, a risk assessment should be undertaken in conjunction with the transplant centre clinicians as to how they will manage their patient. This should include awareness of the timing of the return of the donor from the mosquito-borne virus risk area, the likelihood of receiving a mosquito-borne virus positive donation (with its associated risks) from an asymptomatic donor, and the option of delaying the clearance of the donor and stem cell collection plus conditioning of the patient as far as possible towards day 28 of the return of the donor.

In a situation where a risk assessment is being undertaken to clear a donation for clinical use before the preferred 28-day return from a mosquito-borne virus risk area due to urgent clinical need, consideration should be given to referring samples for any relevant available laboratory testing (e.g. to the Porton Down reference laboratory). Please note, if testing for these viruses (if available) is negative, it does not necessarily mean there is no risk of transmission at less than 28 days post travel.

Chikungunya, Dengue, Yellow Fever and Zika viruses are spread by the day-flying mosquito species Aedes aegypti and Aedes albopictus.

These mosquitos are typically found in tropical and subtropical regions including the Caribbean, South and Central America, Mexico, Africa, the Pacific Islands, South East Asia, the Indian sub-continent, Hawaii and northern parts of Australia.

The range of Aedes albopictus is increasing into more temperate zones, leading to outbreaks of mosquito-borne virus disease in new areas. This includes seasonal outbreaks of Dengue and Chikungunya in parts of Europe. The GDRI entry for mosquito-borne virus risk areas will indicate whether a risk should be applied all year or can be applied seasonally.

Position statements on mosquito-borne viruses are available.

Chikungunya Virus:

Chikungunya is an alphavirus that can cause a wide spectrum of disease. This may range from no or minimal symptoms to death. Most commonly it causes arthritis (typically in the knee, ankle and small joints of the extremities), high fever and a maculopapular rash.

Chikungunya Virus is found in countries in Asia, Africa, Central and South America, and in the islands of the Caribbean. It is known to be spread by blood in symptomatic cases and, on theoretical grounds, could be spread by transfusion and transplantation of tissues and organs from people with pre-symptomatic or asymptomatic disease. A number of visitors returning from endemic areas to the UK have been diagnosed with this infection.

Dengue Virus:

Dengue Virus is a flavivirus that typically gives rise to abrupt high fever with a range of accompanying symptoms.

Dengue fever (DF) is the most common insect-borne disease worldwide. Dengue is currently considered endemic in over 140 countries.

Overall, up to 75% of cases are asymptomatic or mild. If symptoms occur, they can range from non-specific acute febrile illness to severe disease including dengue haemorrhagic fever and dengue shock syndrome. Mild cases may be misdiagnosed as other febrile illnesses.

Yellow Fever Virus:

Yellow Fever Virus is a flavivirus which is found in Africa, South America, Central America and parts of the Caribbean.

Symptoms of Yellow Fever include high temperature, headache, nausea and vomiting, muscle pains and backache. One in four individuals may suffer from jaundice and bleeding from the gastrointestinal tract and other sites.

Zika Virus:

Zika Virus is a flavivirus which was known to occur in Africa and parts of Southeast Asia. More recently, Zika Virus has been associated with epidemic outbreaks in the Pacific region and in the Americas. As well as mosquito-borne infection, Zika Virus can be spread through sexual transmission.

Infection is usually asymptomatic or presents as a mild self-limiting febrile illness. More severe disease and hospitalisation are rare but infection during pregnancy carries a high risk of congenital abnormalities in the baby. Zika Virus infection may be mistaken for Chikungunya or Dengue infections as these viruses often co-circulate.

Reason for change:
Entry renamed from ‘Tropical viruses’ to ‘Mosquito-borne viruses’ with equivalent changes to terminology throughout the text. The deferral period after illness in a mosquito-borne virus risk area has been reduced from 6 months to 4 months. Information about seasonal risk has been added to ‘Additional information’.
Version details:

BM-DSG Edition 203 Release 60 (11 August 2026)