[Vertebrate Pests] The Sparrow and Community Health
By Bobby Corrigan
Most times, people pay little attention to the seemingly “ordinary” house sparrow (Passer domesticus) that co-inhabits our cities and towns. In fact, because birds in general are one of the lucky species considered by humans as “desirable” and/or “friendly” animals, the house sparrow is commonly granted unusually close access to our own lives and thus indirectly to our own food. Consider, for example, our reactions to sparrows in our proximity vs. snakes, spiders, rats or mice.
Being this accepting of the house sparrow would be okay if it were simply another bird that sings in the trees nearby our buildings. But unfortunately, the sparrow has adapted too well to our urban environments. And it is one of nature’s best opportunists in the manner in which it forages for food and where it can locate its nest. Unfortunately, it is this adaptation that renders the house sparrow a potentially important — but often overlooked — urban health pest.
Those of us involved in community health and food safety programs, (i.e., pest management professionals, state and city health inspectors, retail store staff, corporate QA staff, etc.) however, cannot be among those who overlook this little bird and its potential for transmitting diseases.
So, let’s examine the urban sparrow a bit more closely.
BAD HABITS. Like commensal rodents, the house sparrow is also an opportunistic forager. And also like rats and mice, the urban sparrow utilizes the food garbage of people. Most everyone has witnessed how sparrows so adeptly forage about the garbage cans of homes and businesses. Of particular significance is that current day sparrow populations are so common and numerous around our shopping malls and grocery retail stores where thousands of people shop each and every day.
Because the sparrow is primarily a ground forager, it will periodically forage (or step) on the excrement of various animals such as dogs, cats, wildlife and other birds. While flitting about on pavements, parking lots and soil, the sparrow can pick up on its feet and body any of the various micro-organisms lying on these surfaces. Certainly our exterior ground zones contain a mish-mash of spilled or decaying food films and fragments. They also are the receiving beds for the sputum and expelled mucus of people. (Sit in a parking lot and watch shoppers come and go.)
And sparrows don’t restrict themselves to the ground. They also flit up and onto aerial areas and elevated objects such as commercial food waste
DUMPSTERS. Pest professionals and health inspectors know all too well how repulsive the insides of waste Dumpsters are. These areas are repulsive because of the odor associated with organic decay. And as any microbiologist will quickly point out, decaying organic matter is the world in which pathogenic microbes thrive.
In the more aerial areas, sparrows are active on building ledges, roof tops and urban trees, bushes, and vines. Because many birds use these areas, they usually contain both fresh and old bird manure of not just other sparrows, but of pigeons, starlings, crows and gulls. On commercial roof tops, in particular, bird manure often stagnates in moist soupy pockets from rain and snow (yet another ideal breeding medium for many microbes).
You get the picture. It’s not a pretty one. The daily habits of the house sparrow are highly conducive to periodically encountering a multitude of germs — some of which if transferred to us, can harm, and without exaggeration, even kill us.
EFFICIENT TRANSFER. So how efficient is the sparrow at transferring microbes to other animals and to the general environment? Well, the sparrow is, as the saying goes, “a natural.” We all learn in grade school that birds are essential animals in the dissemination of flowers, trees and plants. Birds carry seeds on their bodies and wings until they fall off in flight, or are disseminated via the droppings. Birds even re-stock ponds and lakes with fish via transferring fish eggs on their feet and legs.
And so how much time would it take a sparrow to fly around the entire interior area of a local supermarket? Well because the sparrow can cover 14 to 16 miles in an hour, they obviously can do a “fly by” of produce, deli and the meat section all within only a minute or two. A few minutes more and they have flown over the bakery and dairy section.
In my college medical microbiology course, I remember we were told to shake our hair and heads over Petri dishes to observe what might later grow. I’ll never forget that exercise because some of the Petri dishes produced microbial jungles of all colors.
So, what might shake off (down to the food below) the constantly flapping wings of a store bird that just moments earlier was feeding from rotting vegetables outside in the scummy Dumpster or plodding through parking lot mucous?
Moreover, what is aerosolized out the cloaca of the house sparrow each time it defecates while flying about our stores and warehouses?
I have heard shoppers and warehouse employees make jokes about how the sparrow’s dropping just missed them. Missed them? I’m not so sure, I think to myself. Not unless they were wearing a respirator. Because a sparrow’s dropping truly is a “bomb.” A fecal dropping that falls from an overhead door sign or a rafter is airborne and thus along its trajectory, any viruses and/or bacteria within may be separated from the fecal mass. Or, when the fecal mass hits the floor, a shelf, a food can, or someone’s head or body, more fragmentation of the feces into perhaps what can be called “microbial shrapnel” occurs.
ANY SMOKING GUNS? Okay, so we see that the model is there for urban sparrows to pick up and then transfer potential pathogens to humans. But in reality, do they? How much of a disease risk is the everyday sparrow?
Research addressing this question to any sufficient detail by today’s more scientific standards is perhaps best characterized as minimal. But it’s not zero either. It is known that birds carry, transmit or are involved in various stages of the cycles of disease.
Some publications throughout the years have linked the house sparrow to at least 27 different diseases including several responsible for food-borne illnesses. In one study, 92 percent of a group of collected sparrows tested positive for Salmonella (Arch. Environ. Health. 1969:19: 882-884). But it is another relatively recent study that to me has even more significance — particularly as of late. And that is the role of the house sparrow as a potential vector of the food-borne pathogen Campylobacter.
Campylobacter, similar to Salmonella, is a bacterium. And also similar to Salmonella, there are many strains of Campylobacter with a few being particularly troublesome.
The pathogenic strains of Campylobacter can cause Campylobacteriosis, which in general terms is a cause of human gastroenteritis (diarrhea and vomiting). Campylobacteriosis now has gained the No. 1 spot above salmonellosis and E. coli in food-borne illness occurrences. The Centers for Disease Control and Prevention (www.cdc.gov) estimates that there are currently more than 2.5 million annual cases of Campylobacteriosis in the United States, ranking it as the most frequently diagnosed human gastroenteritis event.
But more troublesome with Campylobacter as compared to other food-borne pathogens is that some infections can progress into reactive arthritis conditions and/or the Gullian-Barre syndrome (a disorder of progressive paralysis that can be life threatening).
Of interest and significance, is that some research has shown that 40 percent of urban and 20 percent of rural sparrow populations have tested positive for Campylobacter being present in their bodies (J. Appl. Bacteriology. 1992. 73: 279-285). The specific role, if any, of city sparrows in campylobacteriosis transmission, however, is thus far unresearched and unknown.
It’s not likely that every other sparrow in a food store is a Campylobacter disseminator. But in all government regulations regarding food safety, the law — and rightfully so — defaults to the potential. If food may have been contaminated with filth, it is an FDA violation. With the sparrow activity model discussed previously, it makes sense for our communities to err on the side of safety.
Two rats or mice running up and down each of the aisles of a supermarket would very likely clear the store of all shoppers. Yet two chirping sparrows flying above the aisles not only will not clear the store, but will amuse a significant number of shoppers as they watch “the little cute birds” flying about.
Of course, neither the rodents nor the birds should be tolerated inside any food-handling establishment of any type. But if I had to select the lesser of the evils here, based on each animal’s potential for efficiently transferring microbes, I’m not so sure I would pick the sparrows.
The ecology of human food-borne diseases and urban pests is complex and highly dynamic. So much more research is needed. But for now, I personally feel I have enough information to go on. Whenever I see sparrows perched above the entry ways of our superstores, or the overhead rafters of delivery docks where our food is delivered and staged, I cringe. I don’t particularly care to play the disease lottery.