Biology Now, 2e

342 ■ CHAPTER 19 Growth of Populations

ECOLOGY

I

t is impossible to know when an infected

mosquito bit the first person in Miami-Dade

County, Florida. But on Friday, July 29, 2016,

health officials confirmed that a woman and three

men in a small area north of downtown Miami

had been infected with the Zika virus through the

bite of a local mosquito. It was the moment every-

one had been dreading: the first known cases of

the virus being transmitted by mosquitoes in the

United States. “As we have anticipated, Zika is

now here,” Tom Frieden, the director of the U.S.

Centers for Disease Control and Prevention (CDC),

told reporters that afternoon (Figure 19.1).

By July 2016, Zika had become a household

name. Zika fever, the illness that results from

infection with Zika virus, is a mild sickness

that typically lasts less than a week and involves

fever, red eyes, headache, and a possible rash.

But Zika has another, much more dire effect

on health. A year before the Miami outbreak,

doctors in Brazil had begun noticing an increas-

ing number of infants born with a serious birth

defect known as microcephaly, in which the head

and brain are smaller than expected; they have

not developed properly. Microcephaly can cause

many problems in growing infants, including

seizures, speech and intellectual delays, feed-

ing and movement problems, and hearing and

vision loss. Brazil’s new cases of microcephaly

were soon linked to a rapidly spreading virus

passed through the bite of a mosquito: Zika.

The scientific evidence linking Zika virus and

microcephaly is strong: infected mothers pass

the virus to their fetuses, where it may stunt

brain growth (Figure 19.2). Studies suggest that

infants exposed to the Zika virus in utero are

more than 50 times more likely to be born with

microcephaly than those who are not exposed.

HI

PR

Range of Aedes aegypti mosquitoes

FL

AL

AZ AR

CA CO

GA

IL

IA

KS

KY

LA

MI

MN

MS

MO

NE

NY

NC

ND

OH

OK

OR

SC

SD

TN

TX

UT

VT

VA

WA

WV

ID WI

MT

NV

NM

WY

CT

NJ

DE

MD

NH

RI

MA

IN

PA

ME

Figure 19.1

Range of the mosquito species most likely to carry the Zika virus

Aedes aegypti mosquitoes spread viruses like Zika, dengue, and chikungunya more often than other

mosquito species do.

Q1: What parts of the United States are within the range of the mosquito that carries Zika?

Q2: What areas are not within the mosquito’s range? Why do you think that is?

Q3: Find your own state, and where you are in the state. Are you at risk of contracting Zika?