Recently, the number of people suffering from Zika virus throughout the world has significantly decreased. However, biologists predict that Zika will return with a vengeance, potentially leading to more infections.
Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh Graduate School of Public Health, suggested that Zika will reemerge in due time, just like other arboviruses such as yellow fever and dengue.
“You have big booms, then they drop. Then a few years later, they come back again,” he said, according to The Washington Post.
Scientists first identified the Zika virus in monkeys in 1947. The following year, scientists rediscovered the virus, and named it after the Zika forest in Uganda where it was first discovered in Aedes africanus mosquitoes.
Virologists have subsequently classified Zika as an arbovirus, a type of virus that is transmitted by arthropod vectors such as ticks and mosquitoes. In 2007, the first major Zika outbreak occurred in Yap, a small island in the Pacific Ocean.
The disease can spread in three ways: It can be transmitted through mosquito bites, sex and from a pregnant woman to her fetus.
Common Zika symptoms include fever, rash, headache, and joint and muscle pain.
The disease is not lethal and people typically don’t get sick enough to go to the hospital.
If a pregnant woman contracts Zika and passes it to her fetus, this could cause microcephaly, otherwise recognized as a birth defect in the shrunken size of a baby’s head.
In 2015, based on the increased number of cases of microcephaly, Brazil declared this as a national public health emergency.
Since then, however, governments in collaboration with the Center for Disease Control (CDC) and World Health Organization (WHO) have worked to successfully control the virus.
The number of infections caused by mosquito bites has significantly decreased in countries like Brazil (more than 216,000 cases in 2016, 15,500 cases in 2017), Colombia (106,000 cases in 2015 and 2016, 1,700 cases in 2017) and Mexico (8,500 cases in 2015 and 2016, 1,800 cases in 2017).
With decreasing rates of infection, ministries of health and WHO have begun switching their focus to long term management of the disease and vaccine development.
Albert Ko, professor of microbial epidemiology diseases and medicine at the Yale School of Public Health, predicts that Zika will eventually return.
Ko suggested that herd immunity is to blame for the rise and fall of this disease.
Herd immunity occurs when a large percentage of a population is exposed to an infection but subsequently develops immunity. Even though a portion of the population has not been infected, those people still become immune.
“There are so many people who’ve already been exposed to the virus and are presumably immune, it kind of protects indirectly the people who haven’t been infected,” Ko said, according to The Washington Post.
David Morens, a senior scientific advisor to the director of the National Institute of Allergies and Infectious Diseases, agreed with Ko.
“It’s clear there is some level of herd immunity,” Morens said to The Washington Post. “We see it with all of these arboviruses that cause epidemics. They burn out because the virus can’t find enough people to infect.”
Although herd immunity may protect a population for a given amount of time, some scientists believe that reinfection is possible and that immunity may be temporary.
Others think that Zika may be in the process of finding a new host, such as a capuchin monkey or a common marmoset.
“The Zika virus will be around indefinitely,” Morens said.