Vector = Transmitter of a disease causing organism, an organism
that carries pathogens from one host to another.
Disease = Ill health or abnormal physiology caused by
infection of a pathogenic microorganism (this is a limited definition related to our topic, in more general terms,
disease is caused by a variety of agents not just pathogenic microorganisms).
Pathogen = Infectious organism causing a disease.
Host = Organism in which disease is produced.
Reservoir = Host organism(s) without disease symptoms.
Pathogen persists in the reservoir but does not cause apparent ill effects.
Insects and man have many negative interactions. These include insect competition for our food in the field and
while it is in storage and insect damage to fibers and our shelters by feeding on wood. But perhaps the most important
harmful interaction and the one that causes the most misery and hardship is the connection of arthropods, humans,
and disease.
Historically four arthropod vectored diseases have been very important worldwide. These include malaria, yellow fever, typhus, and the plague. A fifth disease, sleeping sickness is important throughout much of Africa. Worldwide about 1 in 6 people are infected by an arthropod vectored disease. In fact more deaths are attributed to insect vectored diseases than to all the wars ever fought.
A disease of animals, especially birds, monkeys, apes, reptiles and humans. Malaria is an Italian term meaning bad air.
| VECTOR | PATHOGEN | MAIN HOST |
| Mosquitoes in the genus Anopheles
feed from dusk to dawn |
Four protozoan species of of the genus Plasmodium |
Monkeys and birds |
Most subtropical and tropical regions of the world as well as some temperate areas.
Chills, fever, and sweating. In untreated cases, these attacks recur periodically.
Traditionally malaria is found throughout tropical and subtropical and into temperate regions of the world. Since 1950 malaria has been eliminated from almost all of Europe and North America and from large areas in Central and South America. It remains a major problem in parts of Africa and in southeastern Asia. About 100 million cases of human malaria develop each year; about 1 percent are fatal. Recently, the incidence of malaria has been increasing because of increasing resistance to drugs used to control the Plasmodium pathogen.
The primary control method is vector control by the use of residual insecticides. This has changed the distribution of malaria.
Since 1638 the infection has been controlled by treating the patient with an extract from the bark of the cinchona tree, known as quinine. Quinine, which is somewhat toxic, suppresses the growth of protozoans within the bloodstream. Synthetic drugs with lower toxicity and greater efficacy have since been developed.
| VECTOR | PATHOGEN | MAIN HOST |
| Mosquitoes, mainly Aedes aegypti
Day flying, usually in urban areas, some rural |
Virus | Monkeys |
Although the disease may have originated in West Africa, the first records are from Central and South America. Outbreaks have since occurred in North America, Europe and other regions.
The main hosts ( and reservoir for the human disease) are treetop dwelling monkeys and normally the mosquitoes that transmit the pathogen do not encounter humans. When logging occurs however, the treetops are brought to the forest flour and the disease can be transmitted to people.
Non-contagious, infectious disease, caused by a virus, and characterized by headache, backache, and in severe cases by high fever, jaundice, and death.
In cases of spontaneous recovery, convalescence is rapid, although jaundice may persist for some time. The disease never recurs, one attack providing immunity for life.
For 300 years following the Spanish conquests in Central America, yellow fever was one of the great plagues of the world. The tropical and subtropical regions of the Americas were subjected to devastating epidemics, and serious outbreaks occurred as far north as Boston and as far away as Spain, France, England, and Italy.
Yellow fever stymied the first attempt to construct the Panama canal. After several years the French led effort was abandoned because of high worker mortality and sickness. A later American effort was successful when Walter Reed discovered that spread by mosquitoes and he instituted a mosquito control program.
No treatment is known for yellow fever. But a vaccine is available and is very effective. It is required for all persons traveling between endemic regions and other locations.
Rather than being transmitted by a bite from the vector, typhus is transmitted in the insect feces which is scratched into the skin.
| VECTOR | PATHOGEN | MAIN HOST |
| Epidemic typhus | ||
| Human body louse, Pediculus humanis, and rat louse | Rickettsia prowazakii (Rickettsia) | Rats |
| Endemic (Murine) typhus | ||
| Flea, Xenopsylla cheopis |
Rickettsia typhi (Rickettsia) Common in SE and S United States. A less severe form of typhus. |
Norway Rat |
Worldwide, it is associated with people crowded together in filth, cold, poverty, and hunger; with wars and famine; with refugees; prisons and jails; concentration camps; and ships.
The related disease Rocky Mountain spotted fever is endemic to North America and is vectored by ticks.
Symptoms are usually mild in children. Adults experience a variety of symptoms including; headache, loss of appetite, high fever, chills, confusion, nausea, and a rash. Some cases are fatal.
Epidemic typhus has been one of the great disease scourges in human history. Devastating epidemics of typhus occurred intermittently throughout Europe in the 17th, 18th, and 19th centuries. Prominent outbreaks developed during the Napoleonic Wars and during the Irish potato famine of 1846-49. In the early 20th century typhus decreased and then practically disappeared from western Europe as improvements in living conditions and hygiene occurred. The disease remained intermittently epidemic in eastern Europe, the Middle East, and parts of Africa, however. During World War I the disease caused 3,000,000 deaths in Russia, several million other deaths Poland and Romania. In World War II it again caused epidemics, this time among refugees and displaced persons, particularly in the German concentration camps.
Typhus's role in war has been so pronounced that the outcomes of conflicts often was decided by typhus rather than battle. In Napoleons advance into Russia, he began with 450,000 men. At his retreat into Poland he had 80,000 men, most lost to typhus not battle.
A vaccine was developed during World War II and is generally effective. Pesticides to give louse control can be applied to clothing in outbreak areas. Despite vaccination and delousing, typhus is still an ever-present threat to impoverished and destitute peoples in many parts of the world. Best prevention is avoidance of areas where rats or lice may be present.
| VECTOR | PATHOGEN | MAIN HOST |
| Fleas | Bacillus, Pastuerella pestis also called Yersinia pestis or Bacillus pestis | Rodents especially rats |
Worldwide
The disease in man has three clinical forms:
The illness in man varies from severe to mere indisposition to violent death. The mild infections are almost always bubonic; pneumonic and septicemic plague are invariably severe and almost always fatal unless treated.
In the 14th century outbreak known as the Black Death, the number of deaths was enormous, reaching in various parts of Europe two-thirds or three-fourths of the population in the first pestilence. It has been calculated that one-fourth of the population of Europe, or 25,000,000 persons, died from plague during the great epidemic. This 3 times the fatalities in WWI. The Great Plague of London in 1664-65 resulted in more than 70,000 deaths in a population estimated at 460,000. An outbreak in Canton and Hong Kong in 1894 left 80,000 to 100,000 dead, and within 20 years the disease spread from the southern Chinese ports throughout the whole world, resulting in more than 10,000,000 deaths.
Plague is primarily a disease of rodents, and infections of man are accidental. When an outbreak in rodents reduces their population, the rat fleas may transfer to humans and bring the disease with them. At first the cases are sporadic, but under suitable conditions large numbers of persons may be infected.
Called sleeping sickness in humans, is also a disease of cattle and other animals in Africa, which serve as the reservoir for the protozoa. In cattle the disease is called nagana.
| VECTOR | PATHOGEN | RESERVOIR |
| Tsetse flies | Glossina Protozoa, Trypanosoma | Wild hoofed animals |
Two variations of the disease occur in central and western Africa.
In South America, another version of the protozoan, T. cruzi, is transmitted by the triatoma bug (kissing bug) and is called Chagas' disease.
African sleeping sickness begins with a chancre at the site of the insect bite, an accelerated heartbeat, an enlargement of the spleen, and rash and fever. Over the next few months the nervous system is attacked, with accompanying mood changes, sleepiness, lack of appetite, eventual coma, and, frequently, death.
Sleeping sickness is usually fatal to humans as well as to domestic horses, camels, dogs, and mules. Cattle and sheep usually survive but do poorly.
Sleeping sickness is endemic in approximately 25% of Africa. The disease has proven to be extremely difficult to treat and prevent and control of the flies is not practical. A consequence of the disease is that much of Africa has remained wilderness and this has allowed many wild animals to survive.
Avoid bites of tsetse flies.
Insect Transmitters of Organisms That Cause Disease in Humans
| Insect Vectors | Disease Organisms | Disease |
| Order Diptera | ||
| Anopheles, mosquitoes | Plasmodium (Protozoa) | Malaria |
| Aedes, mosquitoes | Virus Virus |
Yellow fever Dengue |
| Culex and Aedes mosquitoes, several species | Virus Filaria (Nematode) |
several Encephalitides, Filariasis, Elephantiasis |
| Simulium, black flies | Filaria (Nematode) | Onchocerciasis |
| Phlebotomus, sand flies |
Leishmania (Protozoan) Bartonella (Rickettsia) Virus |
Kala-azar, Oriental sore, Espundia Verruga Papataci fever |
| Tabanus, horse flies | Bacillus anthracis (Bacteria) | Anthrax |
| Chryops, deer flies | Pasteurella tularensis (Bacteria) | Tularemia |
| Glossina, tsetse flies | Trypanosoma (Protozoan) | African sleeping sickness |
| Order Siphonaptera, Fleas | ||
| Xenopsylla | Pastuerella pestis (Bacteria) | Bubonic plague |
| Nosopsyllus | Rickettsia typhi (Rickettsia) | Endemic typhus |
| Order Hemiptera | ||
| Triatoma and Rhodnius (kissing bugs) | Trypanosoma cruzi (Protozoa) | Chagas' disease |
| Order Anoplura, Sucking Lice | ||
| Pediculus humanis | Pasteurella tularensis (Bacteria) | Tularemia |
| lice |
Borrelia recurrentis (Spiroch.) Rickettsia prowazakii (Ricket.) Rickettsia quinatana (Rickett.) |
Relapsing fever Epidemic typhus Trench fever |
| Source: Peters, T. M. 1988. Insects and Human Society, P. 272. | ||
World Health Organization Division of Control of Tropical Diseases, Jan. 11, 2001
Return to: Entomology home page or topics list
Last updated 11 Jan., 2001
Gary Brewer
Professor and Chair