Infectious diseases are caused by microscopic organisms like bacteria, viruses, parasites, and fungi, which impair the normal state or functioning of the body. The early decades of the twentieth century saw many great advances in treating infectious disease. Polio, tuberculosis, smallpox, and many other diseases which had once killed or disabled thousands of people were virtually eradicated from the U.S. population. Innovative drugs and vaccines brought many other potentially-fatal illnesses under control. Even the once potentially fatal "influenza" had become more of a nuisance than a threat, due to effective vaccines and medications.
In fact, for awhile it looked like modern medicine was winning the battle against infectious disease, and public health officials began to talk about being close to eradicating some of them altogether. However, in recent decades we have seen new and troubling diseases come on the scene — diseases caused by infectious agents that are resistant to many current treatments, or that present a challenge to traditional vaccine technologies.
Prominent among these new diseases is AIDS, whose devastating effects come as much from its suppression of the immune system as from the HIV virus itself. New strains of bacteria that are resistant to standard antibiotics also present a grave challenge to the medical community and the population as a whole. Clearly, a whole new wave of research is needed to find treatments and cures for these new infectious diseases—as well as cost-effective treatments for older diseases which still rage unchecked through poorer populations in less-developed nations around the world.
Current Issues in Infectious Disease Science - AIDS/HIV
AIDS (acquired immunodeficiency syndrome) first surfaced in the United States in 1981 and has since become a worldwide epidemic. The virus which causes AIDS, the human immunodeficiency virus (HIV) attacks the body's immune system, systematically eroding the body's ability to ward off infections and certain types of cancers. AIDS deaths result both from these so-called opportunistic infections and the action of HIV itself, which progressively weakens and wastes the bodies of its victims. More than 790,000 cases of AIDS have been reported in the United States since 1981, and as many as 900,000 Americans may be infected with HIV.
At this point in time, there is still neither a cure for nor a vaccine against AIDS. During the past ten years, however, a variety of highly effective treatments were introduced, consisting of mixtures of drugs designed to interrupt various stages of the HIV virus' process of making copies of itself. These so-called "drug cocktails" would contain RT inhibitors such as AZT, and protease inhibitors such as Ritonavir (Norvir). These mixtures did a great job in reducing patients' levels of HIV virus, often to near-undetectable levels, allowing their immune systems to recover.
Many patients previously considered near death achieved remarkable improvement with these treatments, enough so that they were able to return to their normal everyday lives. Many physicians, encouraged by these results, began to also prescribe the drug cocktails to their patients who were infected with HIV but had not yet progressed to full-blown AIDS, in the hopes that by suppressing the virus early they could prevent the ravages of the later stages of the disease.
However, it soon became apparent that the powerful drugs that make up the anti-HIV cocktails present many serious issues of their own, that make wide-spread long-term drug therapy problematic for many HIV patients. For one thing, many patients experience serious side-effects and toxicity problems from these powerful drugs, some drastic enough that the patient cannot continue the treatment. For another, the course of drugs involved with in the cocktail is complex, requiring taking a number of different medicines at precisely-timed intervals, making it challenging for even the most conscientious patients to keep up with their regimen. And finally, these drugs are also expensive, putting them out of reach of patients who lack health insurance, who are poor, or who live in developing nations—precisely those groups of patients among whom the AIDS epidemic is now raging most fiercely.
Clearly, while the first generation of AIDS treatment was ground-breaking in its effectiveness, there remains an urgent need for newer treatments that are simpler, less expensive, and less prone to adverse reactions. And beyond that remains the goal of a vaccine and a cure. Current work on developing a vaccine is promising; researchers have gotten as far as developing an experimental vaccine model that prevents an HIV-like infection in laboratory animals. And scientists now have a much more detailed picture of exactly how the HIV virus replicates, destroys immune cells, and hides within body tissues so that neither the immune system nor most conventional drugs can find and destroy it. But there is still much work to be done to turn these breakthroughs into saved lives.
Antibiotic-Resistant Diseases
Antibiotic drugs were some of the major success stories of 20th century medicine. Starting with the isolation of penicillin and streptomycin, the first of the antibiotics, these so-called "miracle drugs" made a dramatic impact on the treatment of infectious disease worldwide. In fact, antibiotic medicines were being so effective at combating infectious disease that a number of pharmaceutical companies actually began scaling back their activities in this area, assuming that their job was effectively done.
Unfortunately, many of these companies have felt compelled to come back into the field, for it seems that the antibiotic miracle drugs have become victims of their own success. Due to a number of factors, not the least of which has been widespread over-use and misuse of antibiotics, new strains of bacteria have been evolving which are resistant to many of these drugs. Even more alarming, some of these drug-resistant pathogens have been plaguing hospitals around the world, such that patients already weakened by other conditions are becoming sick with them in the very institutions where one would expect to find a superior level of antiseptic conditions.
The problem is in fact inevitable with any antimicrobial agent, and is at base a simple exercise in Darwinian selection. Bacteria and other microbes reproduce at a rapid rate. When they live in a hostile environment—that is, one in which they are assaulted by an antibiotic medicine—many of them die off, but there are always a few survivors that are hardier than average, or that possess some mutation that confers some greater level of protection against the antibiotic. These survivors then reproduce, passing on the genetic basis of their survival to their offspring. Thus the drug assault actually helps select the parents of a new generation of microbes that has greater resistance to that drug. Let that happen enough generations in a row, and you wind up with a microbe that is effectively immune to that drug, and possibly other drugs that are closely related to it chemically. So it is always only a matter of time before any antibiotic, no matter how powerful, loses its effectiveness as populations of bacteria exposed to it over time evolve resistance to it.
The problem has been exacerbated, as noted above, by the tendency for antibiotics to be overused and misused. A significant number of physicians have made a habit of prescribing antibiotics to their patients even when the illness they present is not caused by bacteria—the classic example being the patient suffering from a viral flu; antibiotics, of course, do not work on viruses, but oftentimes doctors will prescribe them anyway "just in case," or because the patient is unhappy with being told there is nothing to be done except to wait the flu out. And the increased volume of these drugs in use means that the whole process of bacteria developing resistance to them is accelerated that much more.
Patient compliance has also been a recurring problem—despite all the warnings affixed to antibiotic prescriptions instructing the patient to finish the entire course of the drug, many do still stop taking it as soon as their symptoms disappear, or otherwise forget to finish the regimen. And when they do that, only the bacteria most susceptible to that drug are killed off, leaving the more resistant survivors to reproduce and evolve ever-stronger offspring.
This goes a long way towards explaining why hospitals, of all places, find themselves the homes of some of the most virulent and intractable of the drug-resistant bacteria. Think of the huge volume of antimicrobial agents in use at a typical hospital—not only antibiotics, but all the antiseptic preparations and practices. Even in the best-run and cleanest hospital, there is still some statistical chance that a few microbes will survive—and those would likely be extremely hardy, producing super-bugs resistant to even some of the strongest antibiotics currently in the medical arsenal. And sadly, it is being found that many hospitals are not being as nearly perfect in their asepsis as one would hope, producing once again the scenario of accelerated development of resistance.
Clearly at least some of this problem is a public health issue, and can be addressed by renewed efforts to educate both the public and medical professionals about the safe, proper, and appropriate use of antibiotic drugs. But that still does not address the underlying issue that sooner or later any antibiotic drug will lose it effectiveness. That is in fact what happened to the class of "miracle drugs" just prior to antibiotics—the sulfa drugs. They had their heyday in the mid twentieth century, and made impressive inroads into infectious disease. When bacteria evolved resistance against them, they were supplanted by the antibiotics. Now we are starting to see the limits of the usefulness of antibiotics, and the search is on for the next class of drugs to supplant them.
Recognizing the gravity of the problem, scientists around the world have been working hard on this very thing, often exploring novel approaches old and new. A recent line of research, for instance, has been studying the use of live viruses that attack and kill bacteria but cause no disease in humans. This was apparently an idea that was being investigated in the early part of the 20th century, but wound up being shelved when sulfa drugs and then antibiotics proved so successful; now, it's looking attractive again. Other research efforts take advantage of the much more detailed knowledge we currently have of the inner workings of pathogenic bacteria, down to the molecular and genetic level—studying, for instance, a bacterium's reproductive process with an eye to disrupting it, or the process by which it excretes toxins out through its cell walls in the hopes of developing a drug that cannot be so easily discharged.
So while the rise of drug resistance is certainly cause for concern, it is also proving to be a wake-up call to the medical community, to turn its time, energy, and resources to defeat infectious disease once again.
