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Questions about the Zika virus and illness

map showing Western Hemisphere areas reporting active transmission of the Zika virus

Western Hemisphere areas reporting active transmission of the Zika virus as of Jan. 26, 2016

The spread of the mosquito borne Zika virus is occupying the headlines today. First found in Brazil in early 2015, it is now being found throughout much of Central and South America. Reports of increases in microcephaly and Guillain-Barre syndrome in patients who have experienced Zika infections are causing worry in both public health circles and among the public.

This is the largest outbreak of illnesses caused by the Zika virus on record. The illness has been found in parts of Central Africa, South Asia, Southeast Asia and the Pacific Islands. Prior to this, an outbreak on the Pacific island of Yap was the most notable.

Much of what we know about the Zika virus is probably subject to change over the next year or two, just as the Ebola outbreak in West Africa has changed what we know about that illness. The information in this article is what is known by medical and public health authorities at this time. Links are included to provide sourcing and further information.

The Zika Virus

The Zika virus was first discovered in the Zika forest of Uganda in 1947. It is part of the genus Flavivirus, along with many others. It is a relative of the West Nile virus, the Yellow Fever virus and the four Dengue viruses.

It is a virus that is transmitted through the bite of infected, female mosquitoes. The cycle of infection is simple. An infected animal is bitten by a non-infected female mosquito. The mosquito develops an infection but, due to its latent immunity, does not die. The virus builds up in the mosquito’s salivary glands and when the mosquito bites again, the virus is transmitted to the new animal. If the new host has no immunity to Zika, it becomes ill. The cycle will then repeat itself.

Zika infections in non-humans have been documented in Africa. Such infections create a reservoir for the virus. It is unknown if Zika is infecting any animals in the Western Hemisphere at this time.

Graphic showing the cycle of infection between mosquitoes, humans and the dengue virus

The cycle of infection

The Mosquito Vector

At this time, the Zika virus is believed to be transmitted by a variety of mosquitoes belonging to the genus Aedes. The Pan American Health Organization states that various Aedes species are found throughout the Americas, except for Canada and continental Chile.

In the current outbreak, the primary vector is believed to be the Yellow Fever mosquito, Aedes aegypti, which has habitat in the tropical and subtropical areas of the Western hemisphere. The species is also believed to be the primary vector for an ongoing dengue epidemic and a massive chikungunya outbreak in those same regions.

The Yellow Fever mosquito is very closely associated with humans and is believed to almost exclusively bite humans. It is a very aggressive, day feeder. A rough way to estimate where these mosquitoes could transmit illness is to examine historical records of Yellow Fever outbreaks, which have been noted as far north as Boston in the United States.

map of Aedes mosquito habitat in the United States

CDC map of Aedes mosquito habitat in the United States

A second Aedes species is suspected of being a vector for these arboviruses in the Western Hemisphere. It is the Asian Tiger mosquito, Aedes albopictus. It is more cold tolerant than its tropical relative and so it can be found outside of the range of Aedes aegypti. Research done in 2007 in Gabon, West Africa, found Ae. albopictus mosquitoes carrying the Zika virus. Similar research has not yet been done in the Americas.

Zika viral illness / Zika Fever

The illness caused by the Zika virus in humans has been, to date, described as mild. The Centers for Disease Control state that about 80 percent of patients who are infected will have no symptoms. This is a similar statistic to West Nile illnesses.

For those with symptoms, a Zika illness presents with “fever, rash, joint pain, or conjunctivitis (red eyes). Other common symptoms include muscle pain and headache.” The illness lasts about a week and hospitalization is rarely necessary. Social media posts suggest that the rash is accompanied with itching, which can be severe. The itching with rash is similar to that found in chikungunya patients.

There is no cure for a Zika illness. There is no vaccine against the Zika virus at this time. Treatment consists of treating the symptoms, with caution. Since the symptoms are so similar to dengue, aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) should not be used until dengue is ruled out. These drugs could increase the chances of bleeding in a dengue patient.

Microcelephaly and Guillain-Barre syndrome

There are many reports of microcelephaly or Guillain-Barre syndrome coincidental with the outbreak of Zika illnesses in the Western Hemisphere. A direct link to either condition has not, as of this writing, been demonstrated.


Boston Children’s Hospital states “Microcephaly is a neurological condition that occurs because a child’s developing brain doesn’t grow properly.” “Microcephaly is often (but not always) congenital, meaning it is already present at birth.” Because the skull expands as the brain grows, children with microcephaly present with heads that are smaller than normal.

Medscape states “Microcephaly is a Head Circumference greater than two standard deviations below the mean.” The link goes to a calculator for head circumference. In another Medscape article, Laurie Scudder, MS, RN-C, PNP, states:

Microcephaly is defined as a head circumference that measures more than 3 standard deviations below the mean for age and sex. [1] It may also be suspected in full-term newborns and infants under the age of 6 months whose head circumference is smaller than that of their chest. [2]

[1] Behrman RE, Kligman RM, Jensen HB. Nelson’s Textbook of Pediatrics. 16th ed. Philadelphia: WB Saunders; 2000.
[2] Moe PG, Seay AR. Neurologic and muscular disorders. In: Hay WH, Haywood AR, Levin MJ, Sondheimon JM, eds. Current Pediatric Diagnosis and Treatment. 16th ed. New York: Lange Medical Books/McGraw-Hill; 2003.

Brazil is reporting 4,180 cases of microcephaly since October, 2015. This is a massive increase and is being reported as potentially linked to Zika infections in pregnant women. The citation, at the CDC, notes several caveats. The authors believe the incidence of microcephaly in Brazil prior to this to have possibly been under-reported. Prior to the outbreak, measurement of infant head circumference was not routine. Finally, much of the reporting relies upon “history of a nonspecific rash illness during pregnancy”, and not laboratory work.

The Hawaii State Department of Health, on Jan. 15, 2016, issued a press release that confirmed an imported case of Zika illness in that state. The patient was in Brazil in May, 2015, and was pregnant. Her child was born with microcephaly.

In a Jan. 28 piece in Nature, questions are raised about the large number of reports of microcephaly in Brazil. “Jorge Lopez-Camelo and Ieda Maria Orioli, from the Latin American Collaborative Study of Congenital Malformations (ECLAMC), say that the surge might largely be attributed to the intense search for cases of the birth defect, and misdiagnoses, because of heightened awareness in the wake of the possible link with Zika.”

Nature notes that of the 4,180 reports of microcephaly in Brazil, just 732 have been evaluated by public health authorities. Of that total, 270 have had a diagnosis of microcephaly confirmed while 462 cases, 63 percent, have been rejected as “false diagnoses.”

Guillain-Barre syndrome

Guillain-Barre syndrome is described by the National Institute of Neurological Disorders and Stroke as “Guillain-Barré syndrome (GBS) is a disorder in which the body’s immune system attacks part of the peripheral nervous system.” “Guillain-Barré is called a syndrome rather than a disease because it is not clear that a specific disease-causing agent is involved.”

From the Mayo Clinic:

Guillain-Barre syndrome often begins with tingling and weakness starting in your feet and legs and spreading to your upper body and arms. In about 10 percent of people with the disorder, symptoms begin in the arms or face. As Guillain-Barre syndrome progresses, muscle weakness can evolve into paralysis.

Zika virus infection complicated by Guillain-Barré syndrome – case report, French Polynesia, December 2013

ECDC Rapid Risk Assessment – Zika virus disease epidemic: potential association with microcephaly and Guillain-Barré syndrome 21 January 2016

Guillain-Barré syndrome – El Salvador 21 January 2016

The number of medically confirmed cases of Guillain-Barré syndrome is growing as are reports of the condition. The link to a Zika illness is circumstantial at this time. The coincidental increase in GBS with the Zika outbreak exists.

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