Issue
In This Issue >>

Getting to Know the Enemy

Getting to Know the Enemy Page 2

THE NUMBERS GAME

In the Macha lab after an early morning spray catch, Kent is pinning an An. arabiensis to a small, Styrofoam-covered board. On a tiny label paired with each mosquito, Kent's minute script details when, where, how and by whom the specimen was collected. She is also teaching Hamapumbu and another local MIAM employee Kalizya Sinyangwe how to identify Anopheles mosquitoes. Kent notes the setae (hairs) and sclerites (plates) on a pinned mosquito and gives the specimen board to Hamapumbu and Sinyangwe to get a closer look. "The important thing," says Kent, "is to get familiar looking at the real thing versus the printed version." She points out the An. arabiensis's speckled legs and its distinguishing pale spot "in the third dark area of the first vein, towards the apex of the wing." She also notes that An. arabiensis lacks the shaggy mouth parts of some other anophelines.

"I feel so great because from the time I was small I never thought I would have something to do with entomology. I never thought I'd look at mosquitoes," says Sinyangwe, who like everyone else in Macha suffered frequent bouts of malaria in his youth. "It's very great for me."

Adds Hamapumbu: "I'm really glad to be part of this team, to wipe out this brutal, deadly disease."

Mosquito by mosquito, year by year, Norris and Kent are building a rich database of baseline information about An. arabiensis. Their work, made possible through JHMRI support, is the type of basic research that is difficult to get funded by outside organizations. "Funding agencies want to see background data, and we're getting the background data," says Kent.

The entomologists are also getting to know the enemy before new control methods and therapies are tested here. For Norris, the ultimate goal is not to kill every mosquito in the region, but just to shave a little time from the average mosquito's life. Even a few days could tip the dynamics of malaria transmission enough to stop the disease. Norris explains: About two or three days after a female mosquito is born, she mates and soon takes a blood meal. (The 50 to 100 baby mosquitoes in her "egg batch" need the nutrients to develop.) If her first blood meal was taken from a person infected with the Plasmodium parasite, about two weeks later the parasite reaches the mosquito's salivary glands. From there, it can be transmitted to another person. By now, it's day 17 or 18 of the mosquito's life. Under ideal conditions, mosquitoes live only 18 to 25 days.

If the mosquito's first blood meal could be postponed or her life shortened a little, no transmission. No malaria. No children dying. "You don't have to eradicate mosquitoes. You just have to get them to not live as long," says Norris. "It's a game of numbers."

A LASTING REPRIEVE?

Last year, the people of Macha were rejoicing.

Malaria, which had spread virtually unchecked every rainy season for two decades, suddenly became scarce. In 2005, just 159 children were treated at Macha Hospital for malaria; seven died. Just four years earlier, the numbers were dramatically higher: 1,600 children treated and 90 deaths. Phil Thuma, long familiar with Plasmodium's wily survival skills, wasn't ready to proclaim victory. But the Hopkins-trained physician allowed himself great hope.

The dearth of malaria cases coincided with the expanded use of a new artemisinin-based drug and droughts in 2003 and 2005, which drove down the mosquito population. Did the drug or the droughts cause the reduction in malaria?

Thuma had seen droughts before, but never such a drop in malaria cases. He places his hopes on the new drug, Coartem, which the hospital and clinics began prescribing in late 2003. Coartem and other artemisinin combination drugs are based on a Chinese herbal remedy and have replaced chloroquine as the treatment of choice for malaria. Community surveys that Thuma led in 2001 showed that 70 percent of children had the malaria parasite in their blood; today that figure is about 10 percent. "If 70 percent of people are carrying malaria, it doesn't take too many mosquitoes to transmit it," says Thuma. "If only 5 or 10 percent are carrying malaria, then it takes a lot more mosquitoes and a lot more bites to get back up to the same level. That's why I'm optimistic we're not going to go back to these high levels."

Entomologists, on the other hand, argue that malaria ebbs and flows with the mosquito population. More mosquitoes equals more malaria. During the 2005 drought, mosquitoes were hard to find. The MIAM team captured fewer than 100 An. arabiensis—about one per every 12 or 14 huts at peak season. Then the rains came back, and the mosquitoes flourished. In January 2006 alone, they found 250, an average of about one per hut.

Ominously, pediatric malaria cases began increasing at the Macha Hospital, from just a few in January to 25 in February and then 112 in March. Thuma remains optimistic; he's still seeing far fewer malaria cases than in years past. (In February 2003, there were 300 pediatric malaria cases.) If the fall in malaria cases were just a matter of the drought and lower numbers of mosquitoes, Thuma believes that the malaria cases would have popped back up to normal levels soon after the rains returned.

A couple years of good rains will likely resolve the debate. For now, the entomologists are sticking to the mosquito-malaria link. "If there are no mosquitoes, there's no transmission," says Shiff, an MMI associate professor. "Once the rains come, you have mosquitoes and transmission again. The mosquitoes are the heart of the problem."

ART OF THE POSSIBLE

Most researchers expect the fight against malaria to continue for years, if not decades. It is not a simple task. After all, the parasite has been with us since humanity's origins. "There are not going to be any easy answers," says Griffin. "You couldn't say, put all your money into X and you get a magic bullet. That was clear from the beginning. I think everybody has recognized it's going to be a complicated process. That's the reason we thought you need to attack the malaria lifecycle on a basic level from multiple fronts."

On the frontlines in Zambia, children—feverish, chilled and often near death—still come to the Macha Hospital. And to Phil Thuma. "I've always believed in having visions or goals that are nearly impossible to attain because if you aim lower, you're going to reach lower," says Thuma. "I would like to see malaria transmission go down to zero in Zambia, or at least in the Macha area."

He concedes eradicating malaria in Africa would be an immense task. Near impossible. After a moment, however, Thuma rallies his confidence and says, "But let's take one of the deans of the Hopkins School of Public HealthD.A. Henderson, the guy who eradicated smallpox. What if he said, 'Let's just get rid of smallpox just in this one local area?'

"I would maintain you have to think big. Maybe it's not realistic. Maybe it's not pragmatic, but your goal should be to get rid of malaria. Clearly, it will take a lot of resources, a lot of effort to get transmission down to zero, but I'm not willing to concede that it's not possible."

Support JHSPH

The Johns Hopkins Bloomberg School of Public Health strives every day to keep millions of people around the world safe from injury or illness.

Make a Gift

Search