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Major Diseases Transmitted by Insects Malaria Malaria (an Italian term meaning bad air) is a disease of animals, especially birds, monkeys, apes, reptiles and humans. Mosquitoes carry the infective protozoan from monkeys and birds to humans. It occurs in subtropical, tropical and some temperate areas of the world. 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. 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. Yellow Fever Yellow fever is another mosquito-vectored disease. The mosquito infects humans by carrying the virus from monkey to humans. 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. However, when logging occurs, the treetops are brought to the forest floor and the disease can be transmitted to people. 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 Yellow Fever is spread by mosquitoes. He instituted a mosquito control program and the canal was completed. 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. © Florida Agriculture in the Classroom, Inc. Typhus (Typhoid Fever) Rather than being transmitted by a bite from the vector, typhus is transmitted in the insect feces, which is scratched into the skin. When the louse bites, the human it leaves its feces behind. The human scratches the itchy bite and introduces the contaminated feces into the open wound. The human body louse is the transmitter of Rickettsia carried from rats. 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. 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. However, the disease remained intermittently epidemic in Eastern Europe, the Middle East, and parts of Africa. During World War I the disease caused 3,000,000 deaths in Russia, several million other deaths in 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 were decided by typhus rather than battle. In Napoleon's 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. Plague Fleas that carry the bacteria from rodents, especially rats, transmit plague. It occurs worldwide! Plague occurs in three forms: bubonic, characterized by swelling of the lymph nodes (buboes); pneumonic, in which the lungs are extensively involved; and septicemic, in which the bloodstream is so invaded that death ensues before the bubonic or pneumonic forms have had time to appear. 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. © Florida Agriculture in the Classroom, Inc. This is three 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 Province in China and Hong Kong in 1894, left 80,000 to 100,000 dead. 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. Trypanosomiasis Called sleeping sickness in humans, Trypanosomiasis 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. Tsetse flies transmit a protozoa from 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. Prevention is the best option. It involves avoidance of bites of tsetse flies. © Florida Agriculture in the Classroom, Inc. Major Diseases Transmitted by Insects Reading For Content Name ________________________________________________________ Disease Where is it Found? What type or organism causes the disease? What insect transmits the disease to humans? What is the nonhuman host? © Florida Agriculture in the Classroom, Inc. Insect Transmitters of Organisms That Cause Disease in Humans Insect Carriers Mosquitoes Disease Organisms Plasmodium (Protozoa) Virus Virus Filaria (Nematode) Filaria (Nematode) Filaria (Nematode) Disease Malaria Yellow Fever Dengue Fever Encephalitides Filariasis Elephantiasis Black Flies Filaria (Nematode) Onchocerciasis Sand Flies Leishmania (Protozoan) Bartonella (Rickettsia) Virus Virus Virus Kala-azar Oriental Sore, Espundia Verruga Papataci Fever Bacillus anthracis (Bacteria) Pasteurella tularensis (Bacteria) Trypanosoma (Protozoan) Pastuerella pestis (Bacteria) Anthrax African Sleeping Sickness Bubonic Plague Rickettsia typhi (Rickettsia) Endemic Typhus Horse Flies Deer Flies Tsetse Flies Fleas Kissing Bugs Sucking Lice Lice Trypanosoma cruzi (Protozoa) Pasteurella tularensis (Bacteria) Borrelia recurrentis (Spiroch.) Rickettsia prowazakii (Ricket.) Rickettsia quinatana (Rickett.) Tularemia Chagas' Disease Tularemia Relapsing Fever Epidemic Typhus Trench Fever © Florida Agriculture in the Classroom, Inc.