Zika

Zika virus disease (also called Zika fever or simply Zika) is a viral disease caused by the flavivirus of the same name. It was first isolated in 1947, in the Zika forest in Uganda, from which it takes its name.

CAUSES

West Nile Virus (WNV) is a single-stranded RNA virus that belongs to the family Flaviviridae, in the Flavivirus genus. This family includes several important pathogens that can be transmitted by human arthropods, including the Dengue (DENV), Zika (ZIKV), tick-borne encephalitis (TBEV), yellow fever (YFV), and Japanese encephalitis (JEV) viruses.

It is an enveloped, spherical virus of approx. 40-50 nm in diameter, with a double lipid membrane surrounding a capsid core. The genome codes for seven non-structural proteins and three structural proteins: the envelope, membrane, and capsid proteins.

Following the bite of a WNV-infected mosquito, the virus reaches the cells via the bloodstream. It then starts to multiply in the tissues, producing a low-level viremia, which decreases with the arrival of the anti-WNV IgM antibodies. The virus subsequently infects the organs (such as the spleen, liver, kidney, and CNS) and was even detected in the urine of a patient, 8 days after the onset of symptoms.

TRANSMISSION

Zika virus is mainly transmitted through the bites of infected Aedes mosquitos, particularly Aedes aegypti, which is responsible for the spread of other diseases, such as yellow fever, Chikungunya, dengue, and West Nile Virus. This mosquito is mainly prevalent in the tropical and subtropical regions of Africa, South America, the Middle East, Southeast Asia, the Pacific, the Indian Islands, and northern Australia.

The geographical distribution of the mosquito is due to the climatic conditions, which prevent them from living in temperate or cold regions; this could signify a greater spread even to our latitudes as global temperatures rise. There is also a vector capable of moving to these regions, called Aedes albopictus (commonly known as tiger mosquito), but it is not as competent as aegypti at transmitting the virus.

Zika virus can also be transmitted through sexual contact, blood transfusions and organ transplants. A pregnant woman can transmit Zika virus to the foetus during pregnancy or delivery. The virus has also been found in breast milk, but transmission via breastfeeding has not yet been confirmed.

GEOGRAPHICAL DISTRIBUTION

The first major outbreak of Zika disease to arouse global public health interest was reported in 2007, on the island of Yap, in Micronesia.

From 2007 to 2018, Zika virus transmission has been documented in 86 countries in Africa, the Americas, Asia and the Pacific. An element of rising concern within the scientific community has been the steady progression of the infection's geographic distribution in the Americas. In fact, since 2015, the infection has been reported in as many as 33 U.S. countries, infecting more than 1.5 million people in Brazil alone. Zika-associated microcephaly and other foetal malformations now represent a public health emergency of international concern after more than 1,000 cases were reported in Brazil.

SYMPTOMS

The incubation period of Zika is usually between 3 and 14 days.

In most cases (80%), the infection is asymptomatic. When symptoms occur, they are nonspecific, often manifesting as flu-like symptoms, with fever, joint pain, and conjunctivitis. A more characteristic symptom is the appearance of a maculopapular rash.

The possibility of severe symptoms is rare, as is associated mortality. However, cases of Guillain-Barré syndrome have been observed in patients with suspected or confirmed infection.

The most serious effects can occur during pregnancy, when the infection can cause serious damage to the foetus, such as brain defects, microcephaly, limb contracture, eye abnormalities, and hearing loss. The risk of congenital malformations following infection during pregnancy remains unknown; approximately 5-15% of children born to Zika virus-infected women during pregnancy show signs of Zika-related complications.

DIAGNOSIS

Preliminary diagnosis of Zika is based on clinical signs, particularly if there is a history of travel to areas where the virus is endemic. Laboratory diagnosis methods for confirming dengue virus infection may involve detection of the virus, viral nucleic acid,

specific antigens or antibodies.

TREATMENT

No specific antiviral treatment for Zika virus disease is available to date. Treatment is mainly supportive and may include supported hydration, analgesics, and antipyretics. However, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided until it is certain that the patient does not have dengue, to reduce the risk of bleeding.

PREVENTION

Prevention of dengue transmission starts with appropriate preventive behavioural measures, especially during the day, when mosquitoes are most active.

• Use an effective mosquito repellent
  The Centers for Disease Control and Prevention (CDC) recommend repellents with the following active ingredients: DEET (>25%); Picaridin; IR3535; Oil of Lemon Eucalyptus (OLE); Para-menthane-diol; 2- undecanone.
• Keep covered
  Wear clothes that cover the legs and arms; light-coloured clothing is best.
• Check the surrounding environment
  Stagnant water is the perfect habitat for mosquitoes to breed. Make sure there is no stagnant water in discarded tyres or industrial containers, swimming pools, storm drains, plant pot saucers, etc. To reduce the risk of transmission, systematic pest control campaigns to fight the Aedes mosquito population appear to be an essential intervention.
• Read our in-depth article Don't get stung/bitten!

With regard to the prevention of sexual transmission, WHO recommends the following behavioural guidelines:

• People who have travelled to Zika-endemic area should use protection during sexual intercourse for at least for 3 months for men and 2 months for women after the journey, even in the absence of symptoms;
• Before travelling to an endemic area, pregnant women should consult their doctor to assess the possible risks and/or consider postponing the trip.
• Pregnant women travelling to a Zika-endemic area should abstain from sex or use protection for the entire duration of the pregnancy.
• If the partner of a pregnant woman travels to a Zika-endemic area, they should use precautions during sexual intercourse for the entire duration of the pregnancy.

Source: WHO; CDC