The health department that serves Houston is at the forefront of efforts to limit the spread of the mosquito-borne disease, and there’s no ‘silver bullet’

This article is more than 4 years old

This article is more than 4 years old

The 7th of January is a date ingrained in Dr Umar Shah’s mind.

He heads the county health department that serves Houston, Texas, America’s fourth-largest city. Days before, he had received an unusual phone call.

“Our infectious disease staff said: ‘We have a suspected case of Zika,’” he said. “And we sort of scratched our heads and said, ‘Really?’”

Zika in Florida: 10 new cases confirmed amid concern over US response Read more

As most Houstonians celebrated the holidays, staff members confirmed the diagnosis with an outside lab. The process took days. The disease was so uncommon that workers had to sequence the virus’s RNA to confirm it was the tropical disease spreading through Brazil.

On that day, doctors confirmed a Latin American traveller imported the first case to Texas.

“These are dates that are ingrained in our minds,” said Shah. “This is something we’ve been living for the last four or five months.”

Now, at the height of mosquito season, Shah’s team of scientists is the only line of defense against disease-carrying mosquitos in one of America’s buggiest regions. The mosquito hunters have developed sophisticated technologies for rooting out the virus. But they are painstaking, time-intensive and expensive. And Shah says they and other departments around the country need more money and staff immediately.

Shah has shifted funds to begin the Zika response in Harris County and rolled out programs to show people how to protect themselves (largely with bug spray and by emptying standing water). He called for research into Aedes mosquito control, cash to staff his lab, and more academic study of Zika. Experts estimate a vaccine is 10 to 15 years away.

“We need something that is going to allow us to continue to build on the foundation we have,” said Shah. “We don’t want a Christmas gift in December.”

In the House of Representatives, a $622m bill would fund the fight through 30 September by raiding some of the monies originally provided for Ebola response. In the Senate, a $1.1bn bill would provide new money to fight the disease, but Republicans are not receptive. Senator John Cornyn, a Republican from Texas, accused Democrats of wanting a “blank check” to fight Zika. The president asked for $1.9bn in February.

With a 15 July deadline to pass a measure before Congress’s vacation, public health officials are increasingly alarmed.

Zika causes mild symptoms, if patients show any at all. The virus was largely ignored after its identification in 1947. It wasn’t until more than a million Brazilians were infected that the worst impacts of the disease showed themselves.

Now, Zika is believed to cause microcephaly, a severe birth defect that leaves children with abnormally small heads. In some people, it appears to cause the neurological muscle paralysis syndrome Guillain-Barré.

There are no vaccines to protect against the disease, no treatments for Zika after diagnosis, and few tools to fight the mosquito that carries it. Scientists were shocked to learn a mosquito-borne virus similar to West Nile virus could be transmitted sexually.

“What we’ve seen with Zika is it’s kind of wherever you have the confluence of three factors,” said Dr Peter Hotez, dean of the National School of Tropical Medicine and a professor of virology at Baylor College of Medicine in Houston. “Those are: Aedes aegypti mosquitoes, crowding, and, I think, the third factor is poverty.”

Facebook Twitter Pinterest Peter Hotez shows an Associated Press reporter and video journalist areas of Houston’s Fifth Ward that may be at high risk for mosquitoes capable of transmitting the Zika virus in Houston. Photograph: John Mone/AP

In Houston, along the coast of the Gulf of Mexico, the warm, rainy climate is perfect for the endemic Aedes aegypti mosquitoes. More than 4.5 million people live in surrounding Harris County. And it’s a region whose poverty rivals that of hard-hit Rio de Janeiro, Brazil,

with 22.9% of Houston’s residents living in poverty, according to the US Census Bureau and the Instituto Brasileiro de Geografia e Estatística.

“It’s going to Houston, New Orleans, Galveston, Biloxi, maybe Mobile, Tampa, Miami,” said Hotez. “It’s something we’re still trying to get our arms around.”

As of June, Texas counted 42 cases of Zika, all in returning travellers. Across the US, 756 cases have been identified, 11 of which were sexually transmitted. Three American babies have been born with microcephaly, the Centers for Disease Control and Prevention announced.

Since the first case, Shah said, he’s been “attached at the hip” with his mosquito control director, a man who manages the testing of up to 10,000 mosquitoes per day for a raft of potentially deadly diseases, including West Nile virus, St Louis encephalitis and dengue.

“We see this as being the new normal,” Shah said.

Mosquitoes are an ever-present preoccupation in the south. In some states, the bugs are so pervasive that mosquito control officers are elected. Harris County has surveilled mosquitoes for decades.

The Harris County mosquito control division was created by referendum in 1965. Tax-averse Texans agreed to fund the public health initiative after 27 people died and 243 were sickened in an outbreak of St Louis encephalitis (SLE), a mosquito-borne disease that causes brain swelling. As with Zika, there is no treatment specific to the virus, so prevention is the best option.

Twelve years later, when SLE again found its way to Houston, the disease infected 42 people and killed one, an improvement researchers attributed in part to mosquito control efforts.

In Houston, on any given day, entomologists can be found clanking open manhole covers, wading into ditches or walking through backyards of obliging residents. They collect small mesh traps filled with tiny vectors.

The trapped mosquitoes are sorted, sexed, geo-tagged and tested. Seven technicians monitor 268 traps across 27 routes, and each day bring up to 10,000 bugs back to a the health department’s highway-side headquarters.

Until recently, the Culex mosquito, which spreads West Nile virus, was the lab’s main focus. Now, Aedes aegypti has gained renewed importance.

The virology labs in Harris County rival major research institutions. By May, workers were readying a real-time PCR, a machine that allows Zika surveillance to be done in-house, not sent elsewhere in Texas or to the CDC in Atlanta, Georgia.

“Time is of the essence,” said Cheryl Freeman, who directs the lab. “It’s crucial for us to be able to detect the moment” that the virus is present.

Mosquito testing has evolved substantially since the division began its work. In the early years, scientists used a mortar and pestle to grind mosquitoes, before spinning the ground insects in a liquid buffer to extract the viruses. Baby rats were injected with incubated viruses and monitored for signs of illness.

Zika virus vaccine for animals brings hope for human protection Read more

Now, mosquitoes are sent through a tissuemizer, a lab device that shakes vials of mosquitoes until they’re nothing more than liquid to extract samples for testing. A “rapid” test is performed using a dipstick.

The county has a “a pretty sophisticated and fairly well resourced mosquito control division”, said Hotez. “The trouble you face elsewhere on the Gulf Coast is that’s the exception, not the rule.”

The man in charge of the federal government’s response, Dr Lyle Petersen, called the variance in quality of mosquito control “of real concern”.

“Really what we’re dealing with is a patchwork of mosquito control operations in the country of varying quality,” Petersen, director of the CDC’s division of vector-borne diseases, told Medscape News.

Most mosquito control in the US has focused on West Nile-spreading mosquitoes, which tend to come out at dusk and fly above the ground. The Aedes mosquito, by contrast, sticks close to human dwellings, lives at ground level, and comes out during the day.

With West Nile, Shah said, “we still had a silver bullet”. Trucks could go spray at night and catch the Culex mosquito in flight. “We could say ‘boom’. We got the mosquito even though you may not have taken all the precautions.”

“Fast forward to Zika – we don’t have a silver bullet. We cannot spray our way out of this. We can’t send our truck out during the middle of the night because it’s out during the day.”