Zika is a mosquito-borne (meaning that the virus is transmitted by mosquitoes, not that it comes from mosquitoes) virus that infects humans which was originally found in Uganda in 1947 and later became endemic, or native to the particular area, until the early 2000s. The Zika virus is most commonly transmitted through the bite of an Aedes aegypti mosquito (The mosquito can be recognized by white markings on its legs and a marking in the form of a lyre on the upper surface of its thorax.) although it has been known to be carried by other Aedes mosquitoes as well. In February of 2016 the Zika virus was declared a Public Health Emergency by the World Health Organization after becoming a large issue in Brazil along with the rest of South and Central America and areas in tropical or subtropical climates.
The virus, although only asymptomatic in 80% of those infected can to lead to the development of microcephaly in newborn babies as well as Guillain-Barre Syndrome, both which are extremely serious conditions. What’s lead to Zika becoming a global health phenomenon is the neurotrophic (relating to the growth of nervous tissue) nature of the virus and the potential to become endemic in an increasing amount of countries due to the rapid rise in temperatures globally. With no vaccine currently available and prevention oftentimes being unreliable, Zika has potential to infect a lot of people across the world. Zika has become a global health phenomenon despite its small incidence rate and mortality rate as compared to other infectious and neglected tropical diseases that are affecting a much larger population of people and don’t receive as much attention in the media or in public health practices. The incidence rate of Zika in XXX is YYY, in ZZZ is AAA and in the US is BBB. All compared to a NTD like XXX which is killing at a rate of XXX per year.
Classification
Zika comes from a family of viruses call the flavivirus genus. The genus is composed over over 70 viruses including Dengue, West Nile, Yellow Fever and Chikungunya. They share a genetic makeup with positive sense single stranded RNA that stretches 11kb in length, (Yan-Jang 1). Similar to others in the Flavivirus family, Zika is enveloped, icosahedral (20 sided) with a positive-sense single stranded RNA genome, (Schirmer). Positive Sense RNA means that the. Zika also falls under the classification of an arbovirus meaning that it is transmitted by an arthropod vector. Mosquitos are arthropod vectors along with flies, sand flies, lice, fleas, ticks, and mites which all transmit a large number of pathogens.
Both Zika and Dengue are arboviral infections transmitted by the Aedes mosquito. According to the CDC, “Co-circulation of both viruses poses challenges to healthcare providers in distinguishing between the 2 infections. These infections have similar clinical features, including fever, rash, and myalgia. Because most patients enter the primary healthcare setting with nonspecific symptoms, we sought to determine if either infection had distinguishing symptoms, signs, or basic laboratory findings.”
Zika dates back to the mid 20th century when it was first discovered in the blood of a sentinel rhesus monkey from the Zika forest in Uganda, where the virus gets its name from. (Enny S. Paixão) But it wasn’t until five years later that the first case was reported in a human in 1952. → MORE INFO ON FIRST CASE? (Schirmer). Zika was first introduced to South America along with Dengue on sailing ships during the 18th and 19th centuries. → MORE DETAIL Now, it’s endemic to the Pacific, South and Central America, and seasonally within the United States due to the climate making it a viable habitat for the Aedes mosquitoes to thrive (Shirmer).
In 2007, the first known outbreak of Zika in humans was on the Yap Islands, a collection of small islands in the Pacific. In this outbreak, approximately 73% of the population of the island was suspected to have Zika and revealed the epidemic potential of the virus. (Shirmer). A few years later in 2013, a large outbreak occured in French Polynesia where it proved how virulent the virus was. Zika spread rapidly throughout the islands and affected nearly 11% of the population which at the time was about 28,000 people. (Shirmer). Amongst those infected, one person was reported to have Guillain-Barre Syndrome, commonly known as GBS. Following this outbreak, the European Centre for Disease control revealed that there had been a significant increase in the incidence of GBS during and following an outbreak of Zika in the French Polynesian islands (Shirmer). → WHAT WAS THE INCIDENCE RATE OF GBS
By 2015, Zika had become epidemic in Brazil and more and more cases of microcephaly in infants were popping up at an extremely high rate for the rare condition. By early 2016 the World Health Organization (WHO) had declared it a public health emergency and the virus had spread to more than 19 other countries and territories across South and Central America. (Shirmer)
Process of Infection
The Aedes family of mosquitoes is the main vector for transmitting the virus to humans, most frequently during the daylight from dawn to dusk. The female Aedes mosquitoes which thrive in tropical and subtropical regions, look for a healthy host to obtain a blood meal from so that can get the protein they for their eggs so they can develop. To identify a healthy host, the aedes mosquitoes are drawn towards hosts that emit chemicals like CO2, NH3, Lactic Acid and Octenol. The mosquito transmits the virus into the blood when the proboscis (an elongated sucking mouthpart that is typically tubular and flexible.) of the mosquito pierces the skin of the host. The proboscis passes through the epidermis and into the dermis layer of the skin where there is vascularization.
The keratinocytes (an epidermal cell that produces keratin), fibroblasts (a cell in connective tissue that produces collagen and other fibers) and dendritic cells (Dendritic cells (DCs) are antigen-presenting cells (also known as accessory cells) of the mammalian immune system. ) welcome the virus into their cells. Once inside the cell, the zika virus injects one single strand positive RNA which is ready to be translated into the cell. Using the cells resources the RNA is translated and then the virus begins to replicate and the host cell eventually dies and that process releases the virus cells.
The mosquito bite and the infection will stay in the bloodstream for about seven days, which is called the incubation period. During this time the host can still pass the virus to another host if another mosquito were to come along and bite them. With most other viruses a host would be considered a dead-end host and they wouldn’t be able to reinfect anyone else. During this time the virus can also be spread through sexual contact.
When a aedes mosquito bites someone who is already infected with Zika it will become infective approximately seven days afterwards. It’s during this time, called the incubation period, in which the virus replicates itself and goes to the salivary glands.The average lifespan of an Aedes mosquito is about two weeks. During that lifetime a mosquito can lay eggs about three times, each time laying 100 eggs. Additionally, eggs can lay dormant for about nine months in the right conditions and remain just as viable with proper water and food (NEA).
Effects of Infection and Treatment
After being infected by Zika, symptoms may include red eyes (also known as conjunctivitis), fever, skin rash, joint pain, muscle pain and headaches. To be diagnosed with Zika, you can be given a blood or urine test. But the treatment is not very advanced. At the moment the only treatment for Zika is to just treat the symptoms that arise. Making sure that you get a lot of rest, lots of fluids and taking pain medications like acetaminophen. “Studies documented that around 80% of those infected were asymptomatic, and in fact, most infected today may not even know they have it” (Rebekah Elliott,)
The most common condition that has been linked to Zika is the development of microcephaly in newborn babies whose mother was infected with Zika during pregnancy. Zika specifically targets the white blood cells and because a pregnant woman’s immune system is already compromised during pregnancy and and when zika enters the bloodstream and it tricks the immune system, suppresses it even more and begins to spread really quickly. In a non-pregnant person the immune system would be able to send the macrophages to the scene and attack and kill the virus because it knows it’s a an invader in the body. In pregnant women, their bodies have sent a lot of M2 macrophages (Macrophages are a diverse group of white blood cells known for eliminating pathogens through phagocytosis, M2 macrophages are alternatively activated by exposure to certain cytokines such as IL-4, IL-10, or IL-13. M2 macrophages will produce either polyamines to induce proliferation or proline to induce collagen production.) to the infection site which tell the immune system to calm down The immune system of a pregnant women creates even more m2 macrophages and so rather than attack the Zika virus, it allows it to propagate (breed specimens of (a plant, animal, etc.) by natural processes from the parent stock.) At this point the virus is spreading throughout the body and passes through the placental barrier and infects the fetus. Normal development of the brain. Because of this condition, there are serious neurological and intellectual deficits, lead to vision, hearing and speech impairments and seizures.
As mentioned previously in this paper, Guillain-Barre Syndrome (GBS) is rare neurological disorder which causes progressive paralysis of the entire peripheral nervous system. Progressive paralysis starts in the feet and moves upward throughout the persons body. The cause of this paralysis is the body’s immune system mistakenly attacks its own peripheral nerves. The peripheral nerves are those that are located outside of the brain and spinal cord. ((https://medbroadcast.com/condition/getcondition/guillain-barre-syndrome) The cause of GBS isn’t fully understood but has been known to follow after infection with viruses (like zika) or bacterial infections. According to the Center for Disease Control (CDC) about 3,000 to 6,000 people develop GBS each year. Most people recover from GBS but age plays a large factor into the recovery rate and extent of recovery. Some patients suffer from permanent nerve damage. GBS can fall on a spectrum of severity, some cases are pretty mild with just a brief weakness and some result in devastating paralysis leaving patients unable to break independently (ninds.nih.gov).
Treatment and Prevention
At this point there is no vaccine for Zika, but researchers are working hard to create one. The best way to avoid getting infected with Zika is to take precautionary measures, especially if you’re pregnant. If you don’t live in a region where Zika is endemic, it’s important to think about what measures you need to take if you plan on traveling to somewhere where it’s endemic and if it’s worth the risk. To avoid getting zika is to avoid getting bit by the aedes mosquitoes and make sure that you are having protected sex so it can’t spread through sexual contact. To avoid getting bit by the mosquitoes it’s best practice to keep your skin as covered up as possible by wearing long sleeves and pants as well as using natural mosquito repellant sprays, making sure to be wary of spraying young children and infants. It’s also best to sleep under a net to make sure you’re not bitten while you’re asleep.
Another precaution is to make it harder for mosquitoes to breed. They often breed near still water, so you should do the mozzie wipe out of your potted plants and any container that catches water. That wipeout includes turning the pail, tip the vase, flip the flower pit, loosen hardened soil and clear the gutters and spray with pesticide.
Climate Change
It’s also important to keep in mind that just because you don’t live in a tropical or subtropical climate right now, doesn’t mean that Zika couldn’t become endemic to your area soon. With the rise in the earth’s overall temperature weather patterns are becoming more extreme and climate is changing which makes a larger number of countries more susceptible to an endemic.
In a study done in Ecuador focused on a 7.7 magnitude earthquake that struck the coastline in April 201six that coincided what a strong El Nino event. Sorensen, a clinical instructor in emergency medicine at CU Anschutz, said, ‘We were seeing all of these viral symptoms in the wake of the quake…We noticed a huge spike in Zika cases where the earthquake occurred. Prior to this, there were only a handful of Zika cases in the whole country.’ Researchers concluded that the number of Zika cases had increased 12-fold in the are of the quake.
‘We saw so many people affected by the earthquake that were sleeping outside without any shelter from mosquitoes, so we were worrying that the region’s changing climate could facilitate the spread of diseases…Natural disasters can create a niche for emerging diseases to come out and affect more people.
Annotated Bibliography
- Araujo, L. M., Ferreira, M. L., & Nascimento, O. J. (2016). Guillain-Barré syndrome associated with the Zika virus outbreak in Brazil. Arquivos De Neuro-Psiquiatria, 74(3), 253-255. doi:10.1590/0004-282×20160035
- Climate change may accelerate infectious disease outbreaks, say researchers. (2017, October 12). Retrieved from https://www.sciencedaily.com/releases/2017/10/171012122835.htm
- Caminade et al., Global risk model for vector-borne transmission of Zika virus reveals the role of El Niño 2015. (2017). Proceedings of the National Academy of Sciences, 114(7). doi:10.1073/pnas.1700746114
- Distinguishing Zika and Dengue Viruses through Simple Clinical Assessment, Singapore – Volume 24, Number 8-August 2018 – Emerging Infectious Diseases journal – CDC. (2018, July 18). Retrieved from https://wwwnc.cdc.gov/eid/article/24/8/17-1883_article
- Elliott, R., Banerjee, T., & Santra, S. (2018). Zika: An emerging disease requiring prevention and awareness. PLOS Neglected Tropical Diseases, 12(6). doi:10.1371/journal.pntd.0006486
- Guillain-Barré Syndrome – Causes, Symptoms, Treatment, Diagnosis. (n.d.). Retrieved from https://medbroadcast.com/condition/getcondition/guillain-barre-syndrome
- Guillain-Barré Syndrome Fact Sheet. (n.d.). Retrieved from https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Guillain-Barré-Syndrome-Fact-Sheet
- Harris, A. A. (2016). History, Epidemiology, and Clinical Manifestations of Zika: A Systematic Review. The Journal of Emergency Medicine, 51(2), 216. doi:10.1016/j.jemermed.2016.06.035
- How Zika Infection Drives Fetal Demise. (n.d.). Retrieved from https://www.hhmi.org/news/how-zika-infection-drives-fetal-demise
- Huang, Y., Higgs, S., Horne, K., & Vanlandingham, D. (2014). Flavivirus-Mosquito Interactions. Viruses, 6(11), 4703-4730. doi:10.3390/v6114703
- One year into the Zika outbreak: How an obscure disease became a global health emergency. (2016, June 13). Retrieved from http://www.who.int/emergencies/zika-virus/articles/one-year-outbreak/en/index3.html
- Southern California Public Radio. (2017, November 11). Zika, HIV attack the immune system in similar ways. Retrieved from https://www.scpr.org/news/2017/08/25/74954/the-zika-virus-undermines-immune-system/
- Schirmer, D., & Kawwass, J. (2016). Epidemiology, Virology, and Pathogenesis of the Zika Virus: From Neglected Tropical Disease to a Focal Point of International Attention. Seminars in Reproductive Medicine, 34(05), 261-265. doi:10.1055/s-0036-1592069
- University of Colorado Anschutz Medical Campus. (2017, October 12). Climate change may accelerate infectious disease outbreaks, say researchers: Study of natural disaster in Ecuador showed 12-fold increase in Zika cases. ScienceDaily. Retrieved November 24, 2018 from www.sciencedaily.com/releases/2017/10/171012122835.htm
- Zika. (n.d.). Retrieved from https://www.nea.gov.sg/dengue-zika/zika
- Zika Virus. (2018, October 31). Retrieved from https://www.cdc.gov/zika/index.html
