The science of medical entomology

StoryImage( ‘/Images/Story//Auto-img-11914450576741.jpg’, ‘Photomicrograph by Robert A. Hedeen’, ‘The medical entomologist must be able to identify the type of flea that is responsible for an outbreak of plague (black death) or endemic typhus fever.‘);

Medical entomology may be defined as the science that deals with the relation of insects, arachnids and other arthropods to the causation of pathological conditions in man or the transmission of organisms that may be responsible for such conditions. Veterinary entomology deals with the same problems that occur in animals other than man, and is closely allied with medical entomology as the two fields frequently overlap.

The arthropod involved with may be the direct agent of the pathological condition itself, e.g., scabies mites; intermediate hosts such as mosquitoes for the filarial worm; or as direct vectors of the causative agent itself, as the mosquito is for the virus causing West Nile fever.

The name medical entomology did not become the designation for a field of science until about 1909, for even up until that relatively late date there were so-called “experts” who derided the idea that insects could cause pathological conditions in man, even in the face of overpowering evidence that mosquitoes transmitted malaria and yellow fever. Today, medical entomology is not only recognized as a science in its own right, but it also takes equal rank with some of the older sciences, including public health, tropical medicine and preventive medicine.

I should make it known at this time that my training and most of my professional life has been as a medical entomologist serving in the Army, civilian service or teaching.

The training of a medical entomologist is extensive and involves the acquisition of one or more graduate degrees. The neophyte medical entomologist must have a broad knowledge of general zoology. The training must include general entomology and arachnology, and also in the following fields of biology: protozoology, helminthology (worms), microbiology including virology, and field ecology. He must be a parasitologist in the truest sense of the word. He should have a wider knowledge of invertebrate animals than is usually taught in introductory courses. It is desirable that he understand vertebrate biology, especially mammals, as many insect-transmitted diseases have reservoirs of the causative agent in vertebrates. A thorough knowledge of chemistry, organic, is highly desirable.

Knowledge of these subjects will enable the medical entomologists to cooperate on occasions with other investigators, including, civil engineers, physicians, veterinarians, and others involved in the fields of pubic health and epidemiology. If he plans to work for a group such as the World Health Organization, proficiency in a foreign language is highly desirable. Since the field is so broad, the medical entomologist usually develops a specialty in one particular group.

The following example will illustrate this point: There are hundreds of species Anopheles (the transmitter of malaria) mosquitoes in the world but only a few are capable of transmitting the agent causing the disease that kills more humans each year than any other source. The medical entomologist must be able to determine what species he is dealing with to solve a problem. He sometimes must be familiar with the immature stages of the insect to make the correct identification.

For example, for years, it was known that the mosquito Anopheles maculipennis was the principal transmitter of malaria in all of Europe. Yet, in some places, malaria was present, but in other locales, it was either rare and absent. Then, it was discovered that scientists were dealing with five different species of Anopheles that looked exactly alike in all stages, except for the patterns on the eggs the female laid. Some transmitted, but others were physiologically incapable of spreading the malarial organism. Control efforts were then directed to the transmitters, and not wasted on the unimportant ones, and the rate of malaria in most of Europe was reduced to almost zero.

As previously noted, most medical entomologists become specialists with a particular group of bugs because it is impossible for an individual to be thoroughly familiar with all of the important groups. A flea specialist may be tapped to help investigate an outbreak of plague, and an expert of ticks may be called into service to cope with an outbreak of Lyme disease.

There are relatively few bona fide medical entomologists around, and any student who becomes interested in this field and qualifies will have no trouble finding gainful and interesting employment. I recently read President George W. Bush acquired and was treated for the tick-transmitted Lyme disease. Perhaps we will soon see a tick specialist on the White House staff to accompany the president on his frequent travels.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

from the Oct. 3, 2007, issue

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