The Mosquito Coast

It is early evening in July. The sub-tropical heat of a Gulf Coast day has slackened, and sodium-vapor streetlights are humming and popping into life, bathing the residential world of adolescents on summer vacation in their orange glow. The evenings run together—defined by the loud, high voices of children, the crunch of sunbaked asphalt under bicycle tires, a great deal of unpracticed flirtation, and, if you are lucky, a visit from the mosquito truck.

In East Baton Rouge Parish, these trucks are painted deep red. A spinning safety-light on the roof cuts through the haze of insecticide that billows in the truck’s wake. They arrive with a cough and mechanical rattle, as the sprayer in the short bed of the truck is toggled on. Aside from the mosquitoes they are here to exterminate, these trucks (and the kids who chase them on their bikes), are about the only thing to see on many an urban street as the sun sets upon the long days of summer.

On one such July afternoon, Fred Augustine sits in a red truck, parked beneath a tree for some shade, off of a side street near a wooded lot in the northern part of the parish. Although Augustine’s quarry has wings, he is not hunting mosquitoes today. Augustine is after birds, as a way to get at something else. Because, as he says, in an uncharacteristic display of bravado, “That’s what we do. We hunt virus.”

***

Mosquitoes, for those of us fortunate enough to live in the developed world, are little more than a nuisance, thanks in part to the trucks that trundle through our neighborhoods. But that shouldn’t be taken to mean that mosquitoes, and the always evolving viruses they spread, do not have the potential to pose serious challenges to our wellbeing in the future. Consider this fact about the mosquito, printed on campaign posters from the Bill and Melinda Gates Foundation’s worldwide effort to eradicate malaria (which is actually spread by mosquito-borne protozoa, not a virus): While sharks, on average, kill ten humans a year, these flying, biting vectors of disease account for more than seven hundred thousand. Equipped with a brain smaller than the period at the end of this sentence and a powerful desire to reproduce, the mosquito has, by some counts, been responsible for half of all human deaths. Period. Ever.

Fortunately though, while they can be nasty, most common arboviruses (an abbreviation of arthropod-borne virus, i.e. one spread by mosquitoes)—West Nile, Eastern or Western equine, La Crosse, Dengue—are confined to a disease profile closer to the flu. Some people infected with West Nile, for example, will not show any signs of infection, fewer will develop flu-like symptoms, and less than one-percent will die. A disease like Eastern equine encephalitis is considerably more dangerous. It kills fully a third of those infected; but the already complicated life cycle, which requires the virus to make the species jump from a bird or rodent to a mosquito and then to a human, is a difficult path to navigate. In contrast, the far more virulent global influenza pandemic of 1918 killed fifty million people worldwide and had a lethality rate of between three and six percent.

Then there’s yellow fever, the acute, mosquito-borne viral disease whose lethal history in Louisiana is well-documented. Throughout the eighteenth and nineteenth centuries in South Louisiana, yellow fever remained an ever-present threat that loomed almost every summer. With its semi-tropical climate and the constant flow of people, free and enslaved, through its port, New Orleans was particularly hard-hit; an outbreak in 1853 claimed the lives of more than 7,500 residents. In 1878, an epidemic gripped the entire lower Mississippi Valley, as steamboats carried passengers—and with them a reservoir of the disease—to other cities up and down the river. In his book The Mississippi Valley’s Great Yellow Fever Epidemic of 1878, Khaled Bloom writes that that outbreak produced some 120,000 cases in the lower Mississippi Valley, which resulted in around twenty thousand deaths and, in some cases, wiped out entire communities.

Yellow fever is thought to have originated in Africa and to have been transmitted to humans from primates, vectored by the bite of the female mosquito. Since the last recorded North American outbreak, which occurred in New Orleans in 1905, cases have dwindled as the viral reservoir in the human population has declined due to the development of an effective yellow fever vaccine as well as ongoing efforts to reduce the population of the transmitting mosquito—Aedes aegypti.

In their present form, none of these diseases presents an existential threat to human civilization. But our historical experience with the mosquito, coupled with the messy business of adaptation, means that these diseases, and the insects that carry them, bear watching. Watching is what Fred Augustine does.

***

There is a certain sort of outdoorsman, often encountered in the South, whose manner has been mellowed by a lifetime spent hunting and fishing. By midlife, these men largely favor their fishing rods over their rifles, and a nearly palpable gentleness and empathy for the natural world emanates from them. This mixture of respect and realism is what makes Augustine great at what he does.

Showing supreme patience and care, Augustine untangles a furious young blue jay from the dozens of net strands that hold it. The young bird struggles, nipping at Augustine’s hands, grabbing the latex of his gloves and pulling it back with a pop.

He laughs, “He’s not too happy, but it’s the cardinals you have to watch out for. They are so mean, they bite themselves.”

Pop, goes the latex on the glove again.

Today Augustine will capture twenty-four passerine birds, a term for birds that thrive along the line where woods meets field. He waits for them to fly into his twelve-meter mist net. Set between two poles Augustine has driven into the ground, a mist net is a tool strong enough to slow and stop a bird in flight, but delicate enough to remain almost invisible to a passing cardinal or blackbird.

Occasionally, Augustine will mark a bird with a shiny band of aluminum so the number printed on it can be used to track the bird if it is caught again. More often, he’ll note the bird’s sex and approximate age in a logbook, sterilize a small area near the shoulder with ethanol, and use a syringe to draw around two-tenths of a cubic centimeter of blood. The blood samples will be taken to a lab to be analyzed for the presence of viruses.

For more than a decade, Augustine has worked at East Baton Rouge Mosquito Abatement and Rodent Control. The red spray-trucks are the most familiar element of mosquito control, but the organization’s work has a much broader scope. Aside from high-level collaborations with agencies like the Centers for Disease Control and Prevention and a number of virology and entomology labs, Mosquito Control organizes educational and community awareness events. They also treat homes and spend a surprising amount of time removing mosquito larva from neglected or abandoned swimming pools. The later is accomplished by deploying schools of specially bred Gambusia affinis, a small, larva-eating fish native to Louisiana. They use airplanes to deploy insecticides in areas that monitoring reveals have an active viral population. Some programs monitor bird nests with night-vision cameras to assess the number of times the suspected vector birds are bitten by mosquitoes in a night. The oddly named sentinel chicken has fallen from favor as a means to quantify how often birds acquire diseases like West Nile. However, at one time, chickens in solitary coops stood lonely guard over humanity while it slept.

***

Mosquito abatement programs are just one weapon in a large toolbox of tactics used to contain the spread of arboviruses. Others include aggressive epidemiological tactics, quarantining, and the application of insecticides. Some diseases, including yellow fever, are held at bay by natural forces. Yellow fever is happiest in an Old World primate, so once the disease was eradicated in the U.S., where there is no reservoir host, the yellow fever mosquito, became relatively harmless. Besides, another species of mosquito, Aedes albopictus (the Asian tiger mosquito) has essentially out-competed the yellow fever mosquito in the U.S. since its arrival in 1981.

Despite policies, precaution, and the sometimes-beneficent powers of nature, viruses remain a threat. It is important to understand that any death or illness that comes from a mosquito-borne virus is a waste of that virus’ time. Killing the host thwarts its natural inclination, which is to reproduce and spread, so even though yellow fever has killed millions of humans over the sweep of time, we were never the intended targets. But when the conditions are right for them to thrive, viruses can give a host organism a lot of problems.

When a virus, through the alchemy of natural selection, passes from its original animal host into humans, it has undergone what is called zoonotic transfer, also known as spillover, a problem for humans as well as the virus. Humans are dead-end hosts for most of the viruses transmitted by mosquitoes. The virus can sicken or kill the infected person or, more likely, be overpowered by the immune system. The virus wants to reproduce itself like it does in its familiar bird or rodent host, but the physiology of humans isn’t a great place for the virus to live. We kill it, or it kills us. In its natural host, however, the virus can live without causing a great deal of harm.

That is why a virus can be so dangerous. They linger, unknown and undetected in a marsh rice rat, for instance, until a mosquito bites the rat, becomes infected with a mutated virus capable of zoonosis, and then that mosquito bites a person. That is one explanation for how we got bayou fever, a hemorrhagic fever like Hanta, Ebola or Marburg, that appeared in Hammond in 1976, killed one person, and then slipped back into whatever animal serves as its host. That is where bayou fever will stay until circumstance and chance present it with an opportunity to take another crack at the human immune system. It should be noted that the singular, unfortunate victim of bayou fever might have contracted it through contact with infected rodent droppings. What should also be noted is that we simply don’t know.

***

Meanwhile, Augustine is painstakingly capturing, gathering samples from, and releasing birds. But really, what he and his red-truck-driving colleagues are doing, is hunting virus. The data they collect will form a guide for tracking the diseases of the future because we don’t know why West Nile killed more than ten percent of those who contracted it when the virus first appeared in the United States (via a shipment of infected birds from Israel) but now has a lethality rate of less than one percent. We don’t know where it lives, and we don’t know what it does there; but the same can be said for many diseases that kill fewer than a few hundred people a year.

Among his many other responsibilities, Augustine will contribute records derived from more than fifteen hundred birds a year to what could be regarded as detective work done before the commission of a crime. We know that zoonotic diseases like smallpox, anthrax, and rabies have presented significant challenges to humans in the past and that they affect us to this day. We also know that the landscape they inhabit is constantly changing as species are moved around the globe and that these same species will evolve and adapt to their new surroundings in novel and unexpected ways.

The blue haze of Permethrin from a fog truck, lit by orange streetlights: that is the image that comes to mind if one thinks about mosquito control at all. That is what we see, but it is just the most visible aspect of a complex system for the monitoring and control of one family of flying arthropods. Beyond our immediate, local experiences with these diseases lies the much larger human enterprise of making each part of our world hospitable to the needs of our particular species. It has been a tremendous undertaking and one that has largely benefited humanity. But these diseases and the mosquitoes that carry them remind us that we always bring our problems with us.

Lest We Forget …

Interesting to note that the yellow fever mosquito is still occasionally trapped in Baton Rouge’s Sweet Olive Cemetery and that across North Boulevard from that historic cemetery stands a monument marking the mass grave of nearly one hundred people who died in Baton Rouge’s last yellow fever outbreak. In 1905, New Orleans was the site of the nation’s last significant outbreak; 452 people died.