The Center for Disease Control and Prevention (CDC) says that the detection of the local spread of Zika is difficult. This is because the infected individual may not show likely symptoms until about two weeks after getting infected. The course of disease usually runs for about a week or more. This means that the diagnosis and investigation of cases will take a couple of weeks.
The suspicion of a likely Zika virus infection may be based on the symptoms seen in persons living in or traveled to areas where the virus is circulating. There must be a high index of suspicion by the caregiver. Laboratory tests can only confirm the diagnosis carried out on whole blood, serum, plasma, or other body fluids, including semen, amniotic fluid, cerebrospinal fluid, urine, saliva, vaginal fluids, etc. In screening for the Zika virus, blood and urine sample are more commonly collected for investigations. Positive results in either of the test may confirm the infection.
Research has shown with established proof that the virus can remain present in the semen and urine for longer times than in blood or saliva. Studies are still ongoing to determine the duration of persistence and viability of the virus in cerebrospinal fluid, products of conception, and other body fluids. Hence, the specimen to be collected from any individual presenting for testing will be required to give blood or urine.
The procedure for testing varies depending on the prevalence of the known circulating viruses in the area the patient is exposed to. It is also determined by the available resources and the algorithm of workflow in the laboratory. The WHO recommends the following testing strategies:
- Nucleic Acid Testing (NAT): this is done in patients that present with onset of symptoms in less than seven days. The specimen used is whole blood or serum collected in a dry tube. Urine specimens may also be obtained from patients presenting with the onset of symptoms within seven days. When NAT is used, negative results should be interpreted with care and caution. This is because it does not rule out infection because viremia levels drop rapidly about seven days after the onset of symptoms and may not be detected by the testing technique at the lower end of the sensitivity.
- Serology and/or Nucleic Acid Testing: both are done in patients presenting with the onset of symptoms at day seven or more. It is aimed at the detection of IgM. The specimen is whole blood collected in a dry tube and serum from patients who present with onset of symptoms within or greater than seven days. When it is possible, paired serum specimens should be collected at least 2-3 weeks apart with the first serum specimen collection within the first five days of the illness ideally. Serology is the preferable method on a specimen collected from patients with onset of symptoms greater than seven days.
It is not enough to collect these specimens from the patient. Also, a detailed history of the patient must be taken and appropriate information recorded along with the specimen. This includes the full name, date of birth, address, time and date of collection etc. other information to be collected: symptoms, date, and duration of onset of symptoms, contact and type of contact with known Zika virus cases e. g breastfeeding, sexual partner, blood transfusion, etc.
Also, a comprehensive travel history entailing the dates, place, and duration of the visit should be taken. History of vaccination should be taken too, especially the ones associated with flaviviruses such as yellow fever virus, Japanese encephalitis virus, and if available, Dengue virus.
Another diagnostic testing for Zika is to test for the virus's RNA (a genetic component of the virus), which may be detected in an individual's blood. With this form of testing, screening for Zika virus can be done conveniently. A test can be ordered, without a doctor's referral or insurance, you visit a CLIA-certified U.S. lab, and have your results within 1-3 days.
More importantly, to note is that there are no at-home test kits available in the U.S. market.
If there is an ongoing outbreak, especially in areas with widespread transmission, it will not be cost-effective to test every suspected case. However, the following categories of people should be prioritized for collection and testing of specimen:
- Patients with sexual exposure to a confirmed or probable cause.
- Patients who meet the case definition of a suspected case with neurological disorders.
- Pregnant patients with a history of travel with ongoing transmission of the virus with or without sexual contact with a confirmed or probable cause.
- Pregnant women from areas with ongoing Zika virus transmission with their fetuses known or suspected to have congenital abnormalities involving the brain.
- Neonates with microcephaly or neurological abnormalities born to women with a history of travel to an endemic region during pregnancy or born in areas with ongoing transmission of the virus.
- Babies with mothers diagnosed with Zika virus, especially if breastfeeding and stillbirths or spontaneous abortions from women who have lived in or traveled to an affected area during the period of pregnancy.
Here are proposed testing algorithms by the WHO for dealing with suspected cases of arbovirus infection identified within seven days of onset of symptoms:
The first algorithm is used to confirm the presence of the virus. The presence of the virus may be established using NAT, such as Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), which can detect targets on the virus genome that is specific for Zika virus. Laboratories using a pan-flavivirus assay in combination with gene sequencing, or other conventional molecular methodologies like multiplex assays for flavivirus detection, which are requested to ensure in-house primer sequences have been updated to detect the recent Zika virus lineages. Primer and probe sets for Zika virus-specific assays have also been recorded. The virus should also be tested either sequentially or in a parallel arrangement in addition to dengue and chikungunya because coinfection with the Zika virus along with other arboviruses has been documented.
The second proposed algorithm for suspected cases of arbovirus infection of more than a week duration after the onset of symptoms. Serological testing for this virus should only be conducted by laboratories with years of experience in performing flavivirus serology.
The recommended serological assays include EIAs (enzyme immunoassays) and IFA (immunofluorescence assays) detecting IgM antibodies using viral lysate, cell culture, supernatant, or recombinant proteins as well as neutralization assays such as plaque-reduction neutralization tests (PRNT). PRNT typically provides the highest specificity, but serological assays are subject to cross-reactivity, especially in patients with a positive history of flavivirus infection or immunization. The testing technique for patients presenting in seven days or more after the onset of symptoms focuses on IgM serology due to the availability. IgM detection should be performed in pregnant women in areas of endemic transmission of the virus who might have had contact with the vector or sexually transmitted Zika virus.
If further testing is required and a higher specificity is needed, the use of comparative neutralization. In general, a reactive result showing Zika virus IgM in the absence of IgM to dengue or other flaviviruses is suggestive of recent exposure to the Zika virus. For laboratories with resources for performing PRNT, a four-fold rise in neutralizing antibody titers in the absence of an increase in antibody titer levels to other flaviviruses is further evidence of recent Zika virus infection.
Using the real-time reverse transcription-polymerase chain reaction (rRT-PCR), urine can be tested for the Zika virus. Urine samples to be used are usually less than two weeks following the onset of symptoms. If urine samples were obtained less than a week following symptoms, the serum of the individual should be tested along with the urine samples.
Testing for Zika virus in pregnant women
Testing for the infection in pregnancy is based on some guidelines outlined by the CDC. These guidelines vary from whether pregnant women present with symptoms or are at risk of an ongoing infection.
CDC’s current recommendation is that:
- A pregnant woman with symptoms of Zika, NAT, and IgM testing should be carried out concurrently within 12 weeks of the onset of symptoms.
- If there is no symptom, but you suspect being exposed to the virus, you should have a test done within 2 to 12 weeks either upon return from an endemic area or having had sexual intercourse with a diagnosed man with the Zika virus.
- If you are resident in an endemic region with ongoing risk of exposure, the IgM test should be done during your first prenatal visit and two subsequent visits.
- If an ultrasound scan shows signs of congenital disabilities that is consistent with Zika virus, both NAT and IgM test can be requested. Also, NAT amniotic testing can be done.
Amniotic fluid testing in pregnant women
According to the CDC, testing of amniotic fluid in pregnant women can be done if there is an ultrasound scan finding suggestive of congenital disabilities. However, the sensitivity and specificity of amniocentesis for screening congenital infection aren't clear. And how effective this test would work for the Zika virus remains unknown.
The similarity in the molecular structure and symptoms of the Zika virus when compared with other mosquito-borne, insect-borne, or non-insect borne disease makes it expedient to rule out Zika infection from these diseases.
The possible diseases in this category include:
- Yellow fever
If you tested positive
A positive NAT or IgM test confirms the Zika virus. To avoid infecting others with the virus, you must abstain from unprotected sexual intercourse or use condoms consistently at least six months. More importantly, if your partner is pregnant to avoid transmission of the virus to the developing fetus.
If you were tested positive during pregnancy, it doesn't necessarily mean you will lose your pregnancy or have a baby with congenital disabilities or other complications. However, routine ultrasound is recommended throughout the pregnancy to monitor your pregnancy or signs of any abnormality.
If your baby is delivered with no congenital disabilities, several tests would be run on your baby to ensure all is fine. These tests are:
- Testing for the Zika virus at birth.
- Performing hearing tests before discharge from the hospital.
- Ultrasound scan of the head within the first month of life.
- An ophthalmic examination to rule out any eye condition.
- The hearing nerve (vestibulocochlear nerve) is tested using the automated auditory brainstem response (ABR) within the first month of life.
For babies born with defects of whatsoever, minor or major, are subsequently referred to pediatric neurologists, ophthalmologists, and other specialists for prompt and adequate management.