The troubling return of epidemics

Although modern medicine has greatiy diminished the likelihood of widespread epidemics, in some ways modern technology has made it easier for deadly organisms to infect humans. Today, scientists admit that we have not conquered infectious diseases, or eliminated the possibility of epidemics.

The construction of roads lets people travel easily through areas that were once inaccessible, allowing diseases to spread easily and over great distances.

The spread of disease

Many “new” diseases that can cause epidemics may be traced to changes in ecosystems. In some parts of the world, human beings have recently come into extensive contact with animal and insect disease carriers for the first time.

Unfortunately, this is happening at a time when some infections have become much harder to treat. Certain diseases that could once be controlled have acquired resistance to standard treatments. And in recent decades, humans have ventured into jungles and rain forests where unknown viruses lurk. As a result, humans are now spreading diseases that once infected only the animals of the rain forests. Our modern transportation has also contributed to the rapid spread of infectious diseases. Today, a traveler can unknowingly carry a deadly organism from the rain forests of Africa to another country in a matter of hours.

Diseases fight back

Scientists are concerned that these new viruses and drug-resistant bacteria are reversing medical victories over infectious disease. For example, several drug-resistant strains of tuberculosis (TB), a disease that until recently had been well under control, have emerged in the United States and other developed countries. Drug resistance occurs because any bacterial infection will include some bacteria that mutate. Some of these mutations will, by chance, make some bacteria resistant to one or more antibiotics. A strong immune system will destroy the few bacteria that remain after antibiotic treatment. A weak immune system, however, will allow these bacteria to remain, and perhaps even to pass on their drug resistance to other bacteria. Thus, antibiotic treatment kills off bacteria that are not drug resistant, but can allow drug-resistant bacteria to survive and reproduce. Drug-resistant bacteria have become more prevalent with the increasing use of antibiotics.

Viruses from the jungle

Some of today’s worst medical nightmares are a direct result of human encroachment on once-inaccessible jungles and rain forests. One such disease is Ebola hemorrhagic fever. Ebola is caused by the Ebola virus and is one of the deadliest infectious diseases known, with a mortality rate of up to 90 percent The first recorded Ebola outbreak took place in 1976 in Sudan. Later that same year, a similar disease appeared in villages along the Ebola River in northern Zaire. That epidemic caused hundreds of deaths. Scientists named it Ebola, subtype Zaire. A second outbreak occurred in the same region in 1979, and in April 1995 another Ebola epidemic broke out in the city of Kikwit, Zaire. Scientists have not yet determined how or when the first human host contracted the virus.

Among humans, the Ebola virus is spread by direct contact with infected blood, organs, or secretions. The onset of the disease is rapid, with symptoms occurring a few days after infection. In almost every case, death soon follows.

Frighteningly, Ebola has already traveled to other continents. In Reston, Virginia, U.S., another subtype of the Ebola virus Reston was isolated in a colony of monkeys imported from Mindanao in the Philippines. Monkeys were found to have the disease at Reston in 1989 and 1990. The Reston subtype causes death in monkeys, but although humans develop antibodies to the virus, they experience no symptoms.

Viruses such as Ebola are frightening, but scientists say they are much too deadly to be a serious threat to the world population. Their victims die so quickly that these viruses have little opportunity to infect large numbers of people. However, several other lethal viruses have emerged from the jungle in the past few decades. These viruses may include the most insidious of all the HIV virus, which causes AIDS.

An electrocardiograph of the Ebola virus.

The AIDS virus

Some scientists believe that HIV may have spread to humans from African primates, possibly as early as the 1950’s. In contrast to victims of the Ebola virus, which hits hard and fast, a person may be infected with HIV for years before symptoms appear. During this period, the infected person can transmit the virus to others, mainly through sexual intercourse or direct contact with infected blood.

Thus, HIV has ample time and opportunity to spread. Since AIDS was first identified in the early 1980’s, HIV has spread around the world, infecting an estimated 19.5 million by the mid-1990’s.

A doctor working with the World Health Organization gives a child a malaria vaccination.