Wednesday, February 10, 2016

Emerging and Re-emerging Diseases: Zika Virus


In the group of viruses transmitted through mosquito bites, a new comer has arrived and has people talking about it all over the globe. This emerging virus is called Zika virus. It is related to Yellow fever, Dengue fever and Chikungunya viruses. Like its cousins, Zika virus is not a new virus, it has been present since several years ago. However, it has not shown its epidemic capacity until recently. The World Health Organisation has declared Zika virus a global health emergency.
Zika virus distribution in January 2016

Historical Background
Zika virus was first identified in 1947. Scientists researching for the presence of Yellow fever virus placed a sentinel monkey in a cage in the Zika forest of Uganda. The monkey developed a fever and a transmissible agent was isolated from its serum. This agent was described as Zika virus in 1952. Further studies revealed that humans carried antibodies against Zika virus. The virus was isolated from humans in Nigeria in 1954. Subsequent studies proved the presence of the virus in other African countries (such as Uganda, Tanzania, Central African Republic), as well as Asia (India, Malaysia, Philippines, Thailand and so on).
The Zika virus has since moved outside its area of origin, with outbreaks occurring in 2007 and 2013 in Yap Island and French Polynesia, respectively. The first cases in the Americas were detected in Brazil in May 2015. There are two lineages of the Zika virus: the African lineage, and the Asian lineage. The virus currently circulating in Brazil is the Asian genotype.
Even though the virus has been in existence for many years, it took the outbreak of 2007 for the world to realise the epidemic potential of the Zika virus.  A major outbreak occurred in Yap Island, Micronesia in 2007. This epidemic affected about 5,000 people. More recently, epidemics have occurred in Polynesia in 2013 with about 55,000 people being affected.
In 2007, there was an epidemic of Dengue fever and Chikungunya viruses in Libreville, Gabon. Researches carried out then, showed that the inhabitants of Libreville were infected with Zika virus with the same frequency as the other two viruses. This means that there was a simultaneous epidemic of Chikungunya, Dengue and Zika viruses in Gabon.


Transmission
Zika virus is transmitted among humans by mosquito bites. The implicated mosquito is the daytime-active Aedes mosquito, or tiger mosquito as it is most commonly referred to. Aedes mosquitoes are visually distinctive because they have noticeable black and white markings on their body and legs, hence the name, tiger mosquito. Unlike other mosquitoes, the Aedes mosquitoes are active and bite only during the daytime usually at dusk and dawn, except Aedes aegypti, which can bite at any time throughout the day.  Aedes albopictus was identified as the primary vector for Zika virus transmission in the Gabon epidemic of 2007.

The tiger mosquitoes breed in small bodies of stagnant water such as in broken bottles, abandoned used tires, tins, flowerpots and so on. The Aedes aegypti can breed indoors such as in toilet tanks. The mosquito vector has a wide geographical distribution. It was originally found in tropical and subtropical regions, but now found on all continents except Antarctica.
There has been a lot of confusion as to the modes of spread of the Zika virus. The reality is that research is still ongoing.
There has been an increased rate of birth defects in Brazil since the arrival of Zika virus in 2015. This implies that there is a strong possibility of the virus crossing the placenta to affect unborn babies. There has also been a confirmed case of sexually transmitted Zika virus in Dallas, Texas, USA. Studies done have also shown the presence of Zika virus in the semen of infected people. Brazil health officials recently confirmed that the virus can be passed on through blood transfusion, so officials have discouraged blood donation by infected individuals.


Symptoms
Most individuals infected experience mild or no symptoms. About 25% develop symptoms in 2 to 10 days after infection, including rash (exanthem), fever, joint pain, red eyes and headache. Recovery is usually complete and fatalities are rare.
There are two conditions associated with Zika virus infection that have made the outbreak potentially more serious. Congenital microcephaly is a condition of abnormal smallness of the head which is associated with incomplete brain development. This condition has been associated with Zika virus infection in Brazil. While there are many other causes of microcephaly, there has been a surge in the number of cases during the current Zika virus outbreak in Brazil. Tests carried out on the amniotic fluid of pregnant women with microcephalic fetuses  has tested positive for Zika virus. Scientists at Centre for Disease Control and Prevention have also found Zika virus in the brains of 2 babies with the condition who have died within 24hours of birth. Whether or not Zika virus is responsible for the birth defect is not known.
Zika virus is also said to be associated with the development of Gullain-BarrŅ syndrome (GBS). This is a rapid-onset muscle weakness as a result of damage to the nervous system. The disorder can be life-threatening when the paralysis involves muscles of respiration. There is no clear evidence that the virus causes GBS but the Brazil Ministry of Health has reported increased number of GBS since the appearance of the Zika virus.
Treatment and Control
There is no specific treatment for Zika virus infection. Management involves treatment of symptoms. Patients are advised to get plenty of rest and stay hydrated by taking plenty of fluids. Drugs can be given to eliminate fever and to treat pain.
There are currently no antiviral drugs or vaccines for Zika infection. There is a safe and effective vaccine against a related virus, the yellow fever virus. Genetic modification can be a good approach to making a vaccine. However, testing of such a candidate might require extensive researches that can take years.
The only option to control the spread of the virus is through vector control. Mosquito control is of public health importance to manage the population of mosquitoes so as to reduce the damage to human health. This involves the use of long-sleeved clothing to reduce insect bite, use of insect repellents, mosquito netting, and the use of various types of pesticide sprays. Source reduction involves environmental sanitation and eliminating stagnant water thereby eradicating breeding sites of mosquitoes.
Child in a slum in Kampala (Uganda) next to an open sewer - Photo by I. Jurga https://www.flickr.com/photos/gtzecosan/3110617133
Biocontrol can also be used which involves a direct introduction of parasite pathogens or animal predators that target mosquitoes. For example, mosquitofish and tilapia which feed on the mosquito larvae; dragon flies, lizards and geckos which feed on adult mosquitoes.


Final Words

Zika virus is an old virus that is newly emerging which has great epidemic potentials. It is a disease of public health importance as it has a wide geographical distribution occurring in all the continents of the world except Antarctica. It produces symptoms similar to its cousins Dengue fever virus and Chikungunya virus but in the milder form. Unlike its relatives, Zika virus can be sexually transmitted. There is concern due to the risk of poor brain development in unborn babies. It is time to launch an all assault war on these pesky little insects that have destroyed more human lives than all the terrorist groups combined!
Ripples' Medical MOT Programme gives people living in rural villages in Nigeria the rare chance to receive medical treatment from our team of medical professionals, so they can have check-ups and even be diagnosed with illnesses that they may not have even been aware of. For many, the nearest hospital is inaccessible and so they and their children often suffer from easily treatable conditions.
Rural Africans desperately need your help. With limited healthcare, they are most at risk from epidemics such as the Zika virus. We are so lucky to be able to treat our illness with the advice of our local doctors, but for rural villagers this is currently not an option. Your donation can help us improve the healthcare facilities for thousands of people in the villages that we operate in and save lives in the process. Please visit http://www.totalgiving.co.uk/appeal/medicalmot and make change happen.

*Dr Maryam Nasir Aliyu is currently volunteering with Ripples Foundation and using her medical experience to help us deliver Medical MOT events to communities in Kano State as well as training media apprentices in Kano as part of the Youth Development Programme. 
Dr Maryam Nasir Aliyu Web Developer

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