Zika virus infection (Zika)

From the start of 2017, the vector borne Zika virus infection (Zika) was established in 84 countries and territories in Latin America, Caribbean, the United States of America, Africa, South-eastern Asia and the Pacific. The Zika virus continues to spread geographically to areas where competent vectors are present. Although in general symptoms are mild, during pregnancy Zika virus can lead to complications such as preterm birth and miscarriage and can cause microcephaly or other congenital malformations in newborns.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Case definitions can change by region, depending on other diseases present and how many cases have been confirmed in the area. Case definitions are therefore updated as new information becomes available. Check for the definition in your area.

Suspected case: A person presenting with rash and/or fever and at least ONE of the following signs or symptoms: joint pain (arthralgia); or joint inflammation (arthritis); or red eyes (conjunctivitis).

Probable case: A suspected case with presence of IgM antibody against Zika virus and an epidemiological link.

Confirmed case: A person with laboratory confirmation of recent Zika virus infection: presence of Zika virus RNA or antigen in serum or other samples (e.g. saliva, tissues, urine, whole blood) OR IgM antibody against Zika virus positive and plaque reduction neutralization test (PRNT90) for Zika virus with titre ≥20 and Zika virus PRNT90 titre ratio ≥ 4 compared to other flaviviruses AND exclusion of other flaviviruses.

WHO case definition source of information: https://apps.who.int/iris/bitstream/handle/10665/204381/WHO_ZIKV_SUR_16.1_eng.pdf?sequence=1&isAllowed=y

At the local level a single case of Zika or its complications may trigger action. At state or provincial level, the increase in reported cases above an established baseline for the same week or month in preceding years, or increasing vector density, may indicate impending epidemic activity. At national level, the detection of changes in virus serotype, subtype or genotype distribution, clinical severity or seropositivity rate, or the introduction of a Zika vector into a new ecological niche, are signals that should be investigated without delay.

• Environments where mosquitoes breed such as humid, and semi-humid environments, as well as around bodies of stagnant water in and close to human habitations in urban settings.
• Increased contact between humans and infected mosquitoes, particularly in urban areas can create epidemics.
• Outbreaks of the disease are of particular concern when they occur in overcrowded settings with inadequate water supply and waste management services that allow the mosquitoes to breed easily.
• Children and elderly who sleep outdoors during daytime in endemic areas are at greater risk.
• Unprotected sex.
• Pregnancy in regions where there are Zika epidemics.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

• Infection rate: 73 per cent.
• Symptomatic attack rate among infected: 18 per cent.

• A pregnant woman can pass Zika virus to her foetus during pregnancy. Zika is a cause of microcephaly and other severe foetal neurological defects known as congenital Zika syndrome.
• Guillain-Barré syndrome is more common in adults and males.

Zika virus.

Vector: Mosquitoes (Aedes aegypti and Aedes albopictus) are carrying the Zika virus.

Non-human and human primates are likely the main reservoirs of the virus.

• Vector-borne: Mosquito bite (Aedes aegypti and Aedes albopictus). The mosquitoes usually bite during the daytime (peak biting periods are early in the morning and in the evening at dusk).
• Congenital transmission: During pregnancy from the pregnant women to her foetus.
• Sexual transmission: Unprotected sex.
• Vehicle-borne transmission: Unsafe blood transfusion (very likely but not confirmed).

3—14 days.

Zika virus is present in blood from a few days to one week, but the virus remains in semen longer.

• People with Zika virus infection can have symptoms including mild fever, skin rash, red eyes, muscle and joint pain, malaise or headache. These symptoms normally last for two to seven days.
• Many people infected with Zika virus will not have symptoms or will only have mild symptoms. Estimates suggest only one in five people show symptoms.
• Zika virus infection during pregnancy is a cause of congenital brain abnormalities, including microcephaly (smaller than normal head size). Outcomes in the child depend on the level of brain damage that the congenital Zika syndrome may cause. Other congenital abnormalities may include limb contractures, high muscle tone, hearing loss or eye abnormalities.
• Zika can also cause complications during pregnancy such as preterm birth and miscarriage.
• Zika virus could trigger the Guillain-Barré syndrome, a rare condition in which a person’s immune system attacks the peripheral nerves. Severe cases which result in near-total paralysis are even rarer.

Dengue fever, chikungunya, West Nile virus infection, yellow fever, malaria, poliomyelitis.

• Polymerase chain reaction (PCR).
• Virus isolation from blood samples.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment should be conducted by health professionals.

Important therapy principles include the following:

• Zika virus disease is usually mild and requires no specific treatment.
• People sick with Zika virus should get plenty of rest, drink enough fluids, and treat pain and fever with common medicines. If symptoms worsen, they should seek medical care and advice.
  • Zika virus infection and dengue fever have similar clinical presentations and therefore, care should be taken when administering medications such as aspirin or other nonsteroidal anti-inflammatory drugs (e.g. Ibuprofen, Naproxen). These may increase the risk of bleeding if the case is in fact dengue fever and not Zika virus infection.
• Where dengue and Zika occur in the same areas, all suspected cases, especially pregnant women, should be referred to the health facility.
• There is currently no vaccine available.

Once a person has been infected, they are likely to be protected from future infections.