Zika Virus Infection

Also known as: Zika

Arboviral infection caused by Zika virus (Flavivirus, related to dengue/yellow fever), transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes; also transmissible via sexual contact, vertical (mother-to-fetus) transmission, and rarely blood transfusion.

Most infections are asymptomatic or mild; primary clinical significance lies in congenital Zika syndrome and association with Guillain-Barré syndrome.

Majority (~80%) of infections asymptomatic
Symptomatic disease (when present): mild, self-limiting; low-grade fever, maculopapular pruritic rash (often prominent feature), conjunctivitis (non-purulent), arthralgia (particularly small joints of hands/feet), myalgia, headache, retro-orbital pain
Symptoms typically resolve within 2-7 days

Distinguishing from dengue/chikungunya (co-circulating, overlapping vectors/regions): Zika rash and conjunctivitis more prominent; dengue more likely to cause high fever/severe myalgia/thrombocytopenia/hemorrhagic risk; chikungunya causes more severe/prolonged arthralgia

Complications:

Congenital Zika syndrome (maternal infection during pregnancy, any trimester, highest risk with first-trimester infection): microcephaly, intracranial calcifications, ventriculomegaly, cortical malformations, ophthalmological abnormalities (chorioretinal atrophy), congenital contractures (arthrogryposis), hearing loss, seizures, severe neurodevelopmental impairment
Guillain-Barré syndrome: ascending, symmetric, flaccid paralysis, areflexia; typically develops 1-2 weeks post-infection, autoimmune/post-infectious mechanism
Rare: meningoencephalitis, myelitis

RT-PCR: detects viral RNA; blood (useful within first 3-7 days of symptom onset, viremia is brief) and urine (RNA detectable for longer period, up to 2 weeks, improving diagnostic yield beyond the initial viremic window)
Serology (IgM): from ~day 4-5 onward, but significant cross-reactivity with other flaviviruses (dengue, yellow fever vaccine/infection) complicates interpretation; plaque reduction neutralization test (PRNT) can help differentiate but still imperfect
Testing recommendations vary by context: symptomatic pregnant women with possible exposure should be tested regardless of symptom timing; asymptomatic pregnant women with ongoing possible exposure; testing per local/CDC guidance, often serial testing
Fetal monitoring (confirmed/suspected maternal infection during pregnancy): serial detailed ultrasound (assess for microcephaly, intracranial calcifications, ventriculomegaly), amniocentesis for PCR testing can be considered, neonatal evaluation at birth (head circumference, neurological exam, hearing screen, ophthalmological exam) regardless of ultrasound findings given imperfect prenatal detection

Differentials: dengue fever, chikungunya, other causes of fever + rash (rubella, measles, parvovirus B19, enterovirus), other causes of conjunctivitis.

No specific antiviral treatment: supportive care only.

Symptomatic infection:

Rest, hydration, antipyretics/analgesics: paracetamol preferred initially
Avoid NSAIDs/aspirin until dengue is excluded (co-circulating in same regions, hemorrhagic risk if dengue present and NSAID given); this precaution applies broadly to any acute febrile illness in Zika/dengue co-endemic areas until diagnosis clarified

Pregnancy management:

Confirmed/suspected infection during pregnancy: serial ultrasound monitoring for fetal abnormalities, specialist maternal-fetal medicine referral
Counseling regarding risk of congenital Zika syndrome ; risk estimates vary by trimester and study, highest concern with first-trimester infection though risk exists throughout pregnancy
Delivery planning and neonatal evaluation as above

Guillain-Barré syndrome (if occurs post-infection): managed as GBS generally ;IVIG or plasma exchange, respiratory monitoring (risk of respiratory muscle involvement requiring ventilatory support), supportive care, physiotherapy for recovery phase

Prevention (no vaccine currently available/widely licensed):

Vector control: eliminate mosquito breeding sites, insecticide use, personal protective measures (repellents, protective clothing, screened/air-conditioned accommodation)
Sexual transmission prevention: condom use or abstinence for men returning from endemic areas ; recommended duration varies by guideline (commonly ≥3 months for men, ≥2 months for women post-exposure/symptom resolution, per evolving CDC/WHO guidance) given virus persistence in semen longer than blood
Travel advisories: pregnant women advised to avoid/reconsider travel to areas with active Zika transmission; if travel unavoidable, strict mosquito bite prevention and sexual transmission precautions with partners
Blood donation deferral for travelers returning from endemic areas per local blood bank policy

Public health: case reporting in endemic/outbreak settings, vector surveillance and control programs, pregnancy registries for monitoring outcomes of confirmed maternal infections.

Chancroid

Chancroid is a sexually transmitted genital ulcer disease caused by Haemophilus ducreyi, a gram negative coccobacillus. It is far less common in high income settings than herpes or syphilis but remains endemic in parts of Africa, Asia, and the Caribbean, and is an important cofactor for HIV transmission given the mucosal breach it causes.

After an incubation period of 4 to 10 days, a tender papule develops that rapidly ulcerates. The resulting ulcer is classically painful, with a ragged, undermined, non-indurated border and a friable, purulent base ("soft chancre"), a key distinguishing feature from the painless, indurated chancre of primary syphilis. Ulcers are often multiple, from autoinoculation. Painful, unilateral inguinal lymphadenopathy develops in roughly 50% of cases, which can progress to a fluctuant bubo and spontaneous rupture if untreated.

Diagnosis is largely clinical in endemic settings given limited culture sensitivity and availability. Where facilities allow, culture on specialized media, PCR (most sensitive where available), or Gram stain of ulcer exudate (showing a "school of fish" pattern of gram negative coccobacilli) support confirmation. Given the difficulty of definitive laboratory confirmation, a probable diagnosis is often made clinically when a painful genital ulcer with typical features occurs alongside painful lymphadenopathy, and dark field microscopy or syphilis serology and HSV testing are negative. Co-testing for syphilis and HIV is essential given shared risk context and the frequency of dual infection.

Azithromycin 1 g PO single dose, or ceftriaxone 250 mg IM single dose, are first line
Alternatives: ciprofloxacin 500 mg PO bd for 3 days (avoided in pregnancy and breastfeeding), or erythromycin base 500 mg PO tds for 7 days
Fluctuant buboes should be aspirated through healthy adjacent skin (incision and drainage is generally avoided given delayed healing) to reduce the risk of spontaneous rupture and sinus formation
Sexual partners within the preceding 10 days should be examined and treated empirically regardless of symptoms
Follow up at 3 to 7 days to confirm clinical improvement; ulcers should show symptomatic improvement within 3 days and objective improvement within 7 days, larger ulcers may take over 2 weeks to fully heal
HIV positive patients may require a longer treatment course and closer follow up given a higher risk of treatment failure

Referral: sexual health services for full STI screening and partner notification; surgical input for large or complicated buboes.

Zika Virus Infection

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management