Understanding the Zika Outbreak and Why it's Rapidly Spreading

The virus has spread to Brazil and many places in Latin America and Caribbean

Aedes aegypti mosquitos are seen in a lab at the Fiocruz institute on January 26, 2016 in Recife, Pernambuco state, Brazil. The mosquito transmits the Zika virus and is being studied at the institute.
Aedes aegypti mosquitos are seen in a lab at the Fiocruz institute on January 26, 2016 in Recife, Pernambuco state, Brazil. The mosquito transmits the Zika virus and is being studied at the institute. Mario Tama/Getty Images News/Getty Images

Zika wasn't well known. It suddenly is. Now more and more know the virus, as it circles the globe creating explosive outbreaks of painful joints and fevers. Zika places pregnant women at risk for having babies born with small and underdeveloped brains. 

The US CDC now recommends women in any stage of pregnancy postpone any travel to areas affected by Zika. Countries where transmission is reported include but not limited to: Brazil, Antigua, Aruba, Barbuda, Barbados, Bolivia, Colombia, Costa Rica, Cuba, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Saint Martin, Suriname, Trinidad and Tobago, Turks & Caicos, Venezuela, Puerto Rico.

It has also been seen in Cape Verde, American Samoa, Samoa, Guinea-Bissau, Singapore, Thailand, and Tonga.

The virus has also been found in the US - in Florida (around Miami) and Texas (reported in Brownsville). Travelers have returned with the virus to other parts of the US, but haven't been spreading it - except through sex - to anyone else. The mosquitoes that can spread the virus however are present, even if not as common as they are in some warmer spots. Zika could, though, possibly be transmitted in NY and the Midwest.

Recent History

All of this interest in Zika is relatively new. The virus has recently begun spreading in the Western Hemisphere. It has gathered momentum as it is new to immune systems and there are plenty of mosquitoes to spread it.

Zika reached Brazil - particularly in Bahia - and Vanuatu in the first half of 2015, but likely was there earlier. It looks like it reached Haiti even earlier in 2014, maybe even 2013.

It may have been indolent and slowly brewing elsewhere as well.

Later in 2015, it reached into Paraguay, Colombia, and Venezuela. It also reached into Central America - Mexico, El Salvador, Guatemala, Panama, and Honduras. It is beginning to take steps into the Caribbean, having reached Puerto Rico, Haiti, Barbados and Martinqiue.

There is concern it has reached into further areas in the region, without having been detected by laboratories yet.

The disease is often not recognized. It's mistaken for its better known relatives that cause more severe illnesses. These relatives - Dengue, West Nile, Japanese Encephalitis, and Yellow Fever - also cause fevers after mosquito bites. But Zika is more like Dengue-lite - similar symptoms, less severe outcomes (except for the concerns in pregnancy). Zika can also be misidentified in laboratories as Dengue (and Dengue as Zika) because of antibody cross-reactivity.

Does Zika Cause Birth Defects?

Zika has been associated with microcephaly in babies. This is a birth defect where babies are born with small heads and incompletely developed brains.This possible association has only just been recognized more widely, so the level of risk is not yet quantified.

There is concern among many, including the CDC, that babies born with Microcephaly due to Zika is a risk for pregnant women who live in or travel to affected areas.

Brazil has seen a rise in cases to 10 x what it saw before. Over 3000 cases of babies born with small heads have been reported in Brazil, in areas where the virus had quickly spread. 

The virus is not new, having spread in the South Pacific and Africa before. It may be that these infections were primarily in children, as the virus was common and so caught early in life - and not affecting pregnant women. The viral dynamics - including viral load - may differ in a population that is naive to the virus as well. It may also be that sporadic infection that is often not diagnosed was not connected to Zika. It's hard to recognize the consequences of one, relatively rare infection among many, rather than during an outbreak.

There are many causes of microcephaly. Microcephaly is uncommon. It is also often underdiagnosed. It is not always looked for. The diagnosis depends on what threshold - how small the head is - meets criteria. This birth defect, where babies heads don't develop as normal, can have a lot of causes. It can be due to genes and viruses - like CMV and Rubella - and other infections - like Toxoplasmosis. Microcephaly can be connected to exposure in utero to alcohol and mercury, as well as diseases in the mother, like PKU.

Rates of microcephaly vary around the world based on how common the causes are. It's possible that was already there is now being seen. However, the rates in Brazil are very high. Many babies are born each year in Brazil - around 3 million; 3000 is a high rate of microencephaly anywhere in the world. There is reason to be concerned even though the connection is not definitively proven.

What Does Zika Cause? 

Zika causes a less severe, though nonetheless painful, mix of symptoms reminiscent of Dengue: joint aches and swelling, red eyes, headaches (particularly behind the eyes), a rash, and a fever. It can cause conjunctivitis that is exudative (eyes irritated with discharge). The rash, if present, can be all over the body and quite notable; it may have texture. The fever is often not very high; the thermometer might not register a temperature when someone with Zika feels febrile. Some also lose their appetite, had swollen lymph nodes (especially in the neck), have diarrhea or constipation, become dizzy, have blood in semen ejaculate, or have abdominal or back pain. 

The illness usually develops 3-12 days (often 10) after an infected bite and lasts for 4-7 days (often 5). Many feel particularly tired even after the other symptoms go away. Rash usually begins 3-5 days after the fever.

The virus is not thought to cause symptomatic illness in most affected. Most likely have a very mild syndrome that is not recognized or do not begin ill at all.

It can be associated with more severe consequences - Guillain–Barré syndrome (GBS), though the amount of risk has not been determined. El Salvador has had a rise, as had French Polynesia before it. Some GBS cases may be related to other concomitant viruses like Dengue, which spread in the same locales with the same vectors.

However, for most, who are not pregnant, Zika is generally considered a mild, self-limiting illness that is not usually associated with mortality.

Chikungunya likewise caused problems in pregnancy and newborns, but Zika appears associated with microcephaly, which is distinctive.

If It's Milder, What's the Problem?

There is concern that Zika increases the risk for microcephaly. Brazil reports close to 2000 such cases of microcephaly, normally a rare defect, which many think is related.

It can cause a sudden, explosive epidemic. When Zika hit Yap Island in Micronesia in the Pacific, 3 in 4 were quickly infected. Some were asymptomatic, but many had painful symptoms. This means a community might be suddenly hobbled by most people having a case of painful joints. The disease has never been seen in much of the world so populations would not have any herd immunity.

Where Is It?

Zika is suddenly being noticed around the globe.

Cases have been seen in Brazil, Antigua, Aruba, Barbuda, Barbados, Bolivia, Colombia, Costa Rica, Cuba, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Saint Martin, Suriname, Trinidad and Tobago, Turks & Caicos, Venezuela, Puerto Rico. It has also been seen in Cape Verde, American Samoa, Samoa, Guinea-Bissau, Singapore, and Tonga in the South Pacific and Africa and Asia.

Currently, the virus has been reported to have been transmitted locally inThailand.

Travelers have returned to other areas with the virus, but without spreading, such as has occurred in Texas, New York, Illinois, and Florida. A baby born in Hawaii was found to have microcephaly after the mother had been in Brazil very early in pregnancy.

Parts of Brazil - initially Bahia, in the northeast, first noticed Zika in 2015. Zika has arrived in the region and has begun to spread to other states in Brazil. Any cases of Zika were likely imported by a traveler, whether tourist, business person, or sports fan, from regions where it usually found; Brazil has the mosquitoes that can propagate the continued spread of Zika. Brazil has not previously had any infections. 

Likewise, Vanuatu was shaken by a terrible Cyclone (Pam in March 2015) and 1 month later in April 2015 later had its first case of Zika virus.

The virus has been circulating through the Pacific Islands, oftentimes at the same time as Dengue and Chikungunya. It is new to many of these islands so without immunity from past infections, these outbreaks can be particularly explosive. This outbreak was particularly notable in French Polynesia in 2013.

This followed an outbreak where Zika was identified for the first time as a notable outbreak outside of Africa in 2007, in Micronesia (Yap Island). 

With hindsight, it was realized there were likely human cases elsewhere previously. It has also been noted that parts of the Southeast Asia, including Malaysia, Cambodia, Philippines and Thailand have faced the virus over the years. Indonesia was found to have evidence of the virus as early as the 1970s. 

East, West, and Central Africa have faced the disease over decades. Virus has been identified in Senegal,Gabon,Uganda, Cote d'Ivoire. Antibodies seen, sometimes at high levels, in many locales, possibly indicating past infections in Nigeria, Sierra Leone, Central African Republic, and possibly Pakistan.Virus identified in mosquitoes in Cote d'Ivoire.

Zika has hopscotched around the world on planes. It has travelled from Thailand on multiple occasions to Germany, Taiwan, and Canada, Malaysia to Germany, Indonesia to Australia, French Polynesia to Japan, ItalyUS, and Norway, Senegal to the US

However, if a traveler's viral load (amount of virus in their blood) is too low or the country does not have the right mosquitoes, the virus will not spread. As a result, the virus did not seed outbreaks in these countries.

Where Did It Come From?

Zika was first found in a monkey in Uganda. In 1947, a febrile monkey in a Yellow Fever research project in the Zika forrest in Uganda was found to have a new virus. This became known as Zika virus, but had only been seen in monkeys.

The first known human infection was recognized after a lab accident in 1964

It was subsequently realized that many people have been infected for years with this virus. It was found that many in different  parts of Africa had antibodies to Zika, indicating past (and common) infection. Zika antibodies were found in up to 40% of blood sampled in Nigeria in the late 1960s and early 1970s. It was also found in Uganda, Tanzania, Egypt, Central African Republic, Sierra Leone, and Gabon. As such, many parts of West, Central, and East Africa are affected.

However, antibody tests can corss react with other similar viruses and may not be reliable. Moreover, the virus may be present, but not in people. In Uganda, it's in monkeys, which do not have much contact with people. Even the mosquitoes of the monkeys do not have much contact with people. So the virus is present, but not necessarily affecting people there.

However, as the invasive mosquito Aedes Albopictus, ("Tiger" mosquito) spreads around the globe, it has likely led to outbreaks of Zika in parts of Africa where it was not previously seen. Gabon saw this in 2007.

It was later found that this disease was already in Asia - much like Chikungunya virus, which shares a vector. Antibodies were found in India, Malaysia, the Philippines, Thailand, Vietnam, and Indonesia (including in those recently infected). The virus was clearly circulating in these locations, but the disease was largely off public health "radar".

Outbreaks weren't recognized outside of Africa until the 2007 outbreak in Micronesia where 3 in 4 on the island of Yap were infected. Other outbreaks were then noted in Cambodia in 2010 and French Polynesia in 2013-4 and Easter Island in 2014.

Could It Reach the US?

Yes, it already has. There have been cases in Florida and more recently reported in Texas. The mosquitoes that spread Zika are found in the US, particularly in warmer places like Flordia and Texas, as well as Puerto Rico. They are not as common in the US, though, as they are in some areas where the virus has spread rapidly.

How Is It Transmitted?

Aedes mosquitoes - the ones that transmit Dengue, Chikungunya, and Yellow Fever - spread Zika. Traditionally the virus spread through Aedes aegypti. It has been found to be in mosquitoes that are even more common in North America - Aedes albopictus.

This means anywhere that has had cases of these viruses - such as the Caribbean, South America, even parts of southern Europe, Asia, Florida, Texas (and, in fact, many other parts of the US) could be vulnerable to outbreaks if the virus is introduced (in the right season).

The virus is sexually transmitted. Mosquito-borne illnesses, thankfully, don't usually double as STDs. This is unusual. A researcher developed Zika while in Senegal, returned to the US, and his wife, who had not been in Senegal, then developed Zika, but their children did not. In a later patient, virus was identified in semen, which also contained blood (hematospermia). It has been known to be transmitted, to date, from sex from man to woman, woman to man, and man to man. The virus is also found in urine. It is not thought that sexual transmission causes as much transmission as mosquitoes, who bite a lot.

There is also the possibility of transmission through blood transfusion. Zika, rare in much of the world, is not a standardly screened for. It is possible individuals might donate while they had virus in their blood since the infection can be asymptomatic. A survey in French Polynesia found 3% of donors during an outbreak had Zika in their blood but no symptoms (or at least none at that time). Thankfully screening for malaria and other diseases would preclude many of those infected from donating blood in non-malaria and temperate zones.

Is There Treatment?

Nothing specific. Some require hospitalization if they feel particularly unwell or have other illnesses. There is however some interest in the use of azithromycin.

A Vaccine?

Nope. There's interest in making one. Previous work has shown that the Yellow Fever vaccine is not effective.

How Is It Diagnosed?

An antibody test can be performed to see if there has been an immune response to Zika virus. This is not a common test to order and most doctors won't be able to easily order the test. Where there are outbreaks, it is often assumed that illnesses that seem like Zika are Zika without a lab test, but Chikungunya and Dengue can cause similar illnesses and can spread in the same areas through the same mosquitoes.

Zika is similar to other flaviviruses, like Dengue and Yellow Fever. Antibody tests, like IgM, that detect Zika may cross-react with these flaviviruses, diagnosing someone with Zika virus instead of Dengue or vice-versa. There are other tests which can be used to make sure these antibody tests are accurate by showing how strong a response there is - or how large the titer is - through PRNTs (Plaque reduction neutralization test). Zika can also be identified through direct detection of the virus in blood or other samples.

How to Avoid Zika

Avoid mosquitoes - in particular Aedes mosquitoes, which may breed and live closer to us than other mosquitoes. Avoid these mosquitoes just as you would for chikungunya

Continue Reading