Chikungunya and Zika
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Direct answer
Chikungunya virus is an alphavirus transmitted by Aedes mosquitoes that causes abrupt fever and severe, often prolonged joint pain. Zika virus is a flavivirus, also spread by Aedes, whose main clinical concern is congenital infection causing microcephaly and other brain abnormalities. Both viruses are diagnosed in the early phase by RT-PCR, with serology used for later confirmation.
What you must remember
- Name origin: Chikungunya is roughly a Makonde word meaning that which bends up, describing the stooped posture of patients with joint pain.
- Chikungunya vectors: Aedes aegypti and Aedes albopictus, the latter widely spread across India.
- Chikungunya joints: Acute polyarthritis of the small joints of hands and feet, with arthralgia that can persist for months in some patients.
- Zika discovery: First isolated in 1947 from a sentinel rhesus monkey in the Zika Forest of Uganda.
- Congenital Zika syndrome: Microcephaly, intracranial calcification, eye abnormalities and hearing loss after prenatal infection.
- Guillain-Barré syndrome: Associated with Zika infection in adults as a post-infectious neuropathy.
- Zika transmission: Aedes bites, sexual contact and mother-to-child transmission are all documented routes.
- Serology caution: Zika and dengue IgM antibodies cross-react, so neutralisation testing is needed when serology is ambiguous.
Comparing the two alphaviruses and flaviviruses
Chikungunya and Zika share a vector and a similar early rash, but they belong to different families and cause different complications. The table below sets out the features most often tested.
| Feature | Chikungunya | Zika |
|---|---|---|
| Family and genus | Togaviridae, alphavirus | Flaviviridae, flavivirus |
| Main clinical hallmark | Abrupt fever with severe polyarthralgia | Mild rash and conjunctivitis, often mild or asymptomatic |
| Joint involvement | Symmetrical, often in hands, wrists and ankles | Minor arthralgia |
| Congenital concern | Not a recognised cause of congenital syndrome | Congenital Zika syndrome, including microcephaly |
| Neurological complication | Encephalopathy reported rarely | Guillain-Barré syndrome in adults |
| Early diagnosis | RT-PCR during the viraemic phase | RT-PCR on serum or urine |
| Other transmission | Possible near delivery, when maternal viraemia is high | Sexual and mother-to-child transmission documented |
Chikungunya is primarily a joint disease with a febrile onset, whereas Zika is primarily a disease of the developing brain when it infects a pregnancy. Exam questions usually test the congenital syndrome of Zika and the arthritis of chikungunya, so anchor each virus to its signature complication.
Where the exam tries to catch you
Questions on these viruses usually turn on the complication and the serology trap.
- Trap: Accepting a positive Zika IgM as proof of Zika alone. Correct: Zika IgM cross-reacts with dengue and other flaviviruses, so plaque reduction neutralisation testing is needed for confirmation.
- Trap: Linking chikungunya with a congenital syndrome. Correct: Congenital Zika syndrome is the classic congenital problem, while chikungunya is not a recognised cause of it.
- Trap: Expecting Zika to be severe in most adults. Correct: Most adult infections are mild or asymptomatic, so the main concern is the risk to a pregnancy.
Frequently asked questions
What is congenital Zika syndrome?
Congenital Zika syndrome describes the pattern of defects in infants whose mothers were infected with Zika virus during pregnancy. It includes microcephaly, intracranial calcification, eye abnormalities and hearing loss, and it is recognised by paediatricians and radiologists.
Why is chikungunya arthritis so prolonged?
Chikungunya causes an acute inflammatory polyarthritis of the small joints, and in some patients arthralgia persists for months or longer. Persistent joint symptoms are the main burden of chikungunya, and they are managed with symptomatic treatment and physiotherapy.
How is Zika distinguished from dengue on serology?
Zika and dengue IgM antibodies cross-react, so a positive IgM result alone cannot separate the two infections. Plaque reduction neutralisation testing is used to identify the infecting flavivirus when serology is ambiguous.
Which neurological complication is linked with Zika?
Zika infection in adults has been associated with Guillain-Barré syndrome, a post-infectious immune-mediated neuropathy. The association is a recognised complication rather than a common outcome, and it is one reason Zika is monitored closely during outbreaks.
Which test is used first for chikungunya?
RT-PCR is the test of choice in the first week of illness, when viraemia is highest. IgM ELISA becomes useful later and is the standard test for confirming chikungunya in the convalescent phase.