20 things we now know for certain about the Zika virus

Zika virus exploded into the news with striking images of children born with small heads in Brazil. This was at a time the country was struggling to plan for the Rio Olympics, and also embroiled in political turmoil. These all helped to embed the virus firmly in the public’s mind.

Events have unfolded very rapidly, with shifting certainties and swirling speculations. The storm is however now settling, and a clearer picture emerging. And neurology is right at the centre of this viral catastrophe. What is the current state of play? Here are 20 things we now know about the Zika virus.

1. Zika is an arbovirus of the family Flaviviridae

• ARBOviruses (ARthropod-BOrne) are viruses transmitted by invertebrate animals
• Other Flaviviruses include West Nile, Dengue, and Yellow Fever.
• You guessed right, “flavi” means “yellow”

2. Zika was first identified in Uganda in 1947

 

• The name of the virus comes from Zika forest, “the birth place of the virus”

3. Zika was first isolated from a Rhesus macaque monkey

• Rhesus monkeys have been a goldmine for medical research, most famously for establishing the Rhesus blood group system
• Rhesus macaques are the first primates to go to space, and to be cloned

4. The first human cases were reported from Nigeria

• Three cases of Zika were reported in 1954 from Eastern Nigeria
• A study from 1979 shows a high prevalence of Zika virus in Western Nigeria

5. Outbreaks of Zika have ocurred in Brazil, Micronesia, and French Polynesia

• French Polynesia consists of 118 dispersed islands and atolls
• The largest French Polynesian island is Tahiti

 

6. Zika is mainly transmitted by Aedes mosquitoes

• Unlike other mosquitoes which are nocturnal, Aedes are active only in the daytime
• Aedes are the favourite vehicle for many other Flaviviruses

7. Zika virus is transmitted perinatally

The Centre for Disease Control (CDC) recommendations for pregnant women are

• To avoid travel to affected countries
• To be tested if they travel to affected countries
• To have 3–4 weekly foetal ultrasound if they test positive for the virus
• To have their babies tested at birth if they were infected

8. Zika virus is also sexually transmitted 

• Sexual transmission of the Zika virus is typically male-to-female
• Female-to-male transmission has however been reported
• Men can sexually transmit the infection even when they are have no symptoms

9. Zika virus is most likely transmissible through the skin

• A fatal case report of Zika infection from the New England Journal of Medicine strongly suggests Zika may be transmitted through sweat or tears

10. Zika virus primarily infects neural stem cells

• Neural stem cells (NSCs) produce cells that grow and differentiate into nerve cells
• Invasion of NSCs by Zika virus causes the neurological abnormalities characteristic of the disease

11. Zika infection usually only causes mild and self-limiting symptoms

The typical symptoms of Zika virus infection are

• Fever
• Skin rash
• Conjunctivitis
• Joint pains
• Muscle aches
• Headache

12. Microcephaly is the striking feature of congenital Zika

• Microcephaly is worse if the mother was infected early in pregnancy
• Microcephaly is associated with other problems including seizures, developmental delay, hearing loss, and visual problems

 

13. Zika infection causes several other brain abnormalities

Brain abnormalities with congenital Zika infection include:

• Calcification of the brain’s white matter
• Cerebellar dysgenesis: abnormal development of the cerebellum
• Craniosynostosis: premature closure of the bones of the brain
• Lissencephaly: an abnormal shape of the brain 
• Ventriculomegaly: enlargement of the brain’s fluid-containing spaces

These abnormalities may be seen on brain imaging

14. Adult Zika infection causes Guillain Barre syndrome (GBS)

 

• The association of Zika virus infection with GBS was first reported in 2014
• GBS with Zika virus infection typically presents as acute motor axonal neuropathy (AMAN)

15. Zika virus infection causes other neurological diseases

There are other neurological diseases associated with Zika virus such as

• Acute myelitis
• Encephalitis
• Acute disseminated encephalomyelitis (ADEM)
• Meningoencephalitis
• Miller Fisher syndrome
• Sensory polyneuropathy

 

16. Zika virus infection causes many eye abnormalities

Eye abnormalities reported with Zika virus infection include

• Mottling and atrophy of the retina
• Abnormalities of the optic nerve
• Coloboma (defects) of the iris
• Subluxation (dislocation) of the lens

 

17. Zika virus may cause impairments in other organ systems

Other organs affected by Zika virus lead to disorders such as

• Pulmonary hypoplasia, or underdeveloped lungs
• Severe thrombocytopaenia, or low platelet counts
• Urinary and genital symptoms

18. Zika virus infection is confirmed by laboratory tests

• rRT-PCR (real time reverse transcriptase polymerase chain reaction) is the best test for the Zika virus
• This is done on urine and blood samples collected within 2 weeks of infection

19. There is an experimental human vaccine trial for the Zika virus

 

 

• Zika vaccination in mice has proven successful
• A DNA vaccine named GLS-5700 is undergoing human testing

 

20. There are promising antiviral treatments for Zika virus

• Sofosbuvir impairs Zika virus replication in experimental laboratory tests
• Other promising drugs include Niclosamide, Emricasan, and PHA-690509

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Want to explore more? You may check out the following:

• An excellent review from the CDC via its Emerging Infectious Diseases journal
• The American Association of Neurology (AAN) Zika update page
• 10 Zika Facts You Need to Know from Time magazine
• Zika virus, explained in 6 charts and maps from Vox
• World Health Organisation declares Zika virus a public health emergency
• CDC issues Zika travel notice for 11 Southeast Asian countries 
• CDC whistleblower claims agency has been using wrong Zika test

  

  PS. You can keep a handy track of Zika and other nervous system infections with Neurochecklists