ch21 - ENT 100 Fall 2009 1 Lecture 21 Insects Disease Many...

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Fall 2009 1 Lecture 21: Insects & Disease Many insects and other arthropods are studied because they transmit parasites or pathogens to humans or animals of importance to humans. They are usually referred to as vectors because they acquire and transmit pathogens or parasites from one organism to another. This transmission can occur in a variety of ways and is usually classified by the level of complexity – how does transmission occur, how many different hosts are involved, does the parasite or pathogen undergo reproduction in one or more of these hosts, etc. Transmission: There are two basic modes of parasite transmission by insects, mechanical and biological. Mechanical Transmission Mechanical transmission is the simplest form of parasite or pathogen transmission. Parasites or pathogens are spread by contact with hosts and transmission is usually the result of contamination of the external surfaces of the vector insect. Omnivores like cockroaches and houseflies can frequent areas containing sewage or non-human waste and human food. They have the potential to transmit pathogens from one material to the other simply by walking through it and regurgitating on it. The main limit to mechanical transmission is how long the pathogen remains viable on the outside of the insect. Biological Transmission Biological transmission is the commonest and perhaps most effective form of parasite transmission found in arthropod vectors. In biological transmission the vector plays an essential role in the life cycle of the parasite. The parasite either undergoes multiplication or life stage development in the vector. In essence the vector is really another host for the parasite. In most cases the vector directly injects the parasite into the skin or blood stream of the host. This kind of transmission through the insect vector can also work two ways: vertical and horizontal transmission . Vertical transmission occurs when the pathogen is transmitted from an insect vector to a host animal, such as a bird or human. Horizontal transmission takes place when the female vector passes the pathogen or parasite to her eggs, and therefore offspring, through her ovaries. It was recently discovered that the mosquitoes that transmit West Nile Virus do both vertical and horizontal transmission. As a result the virus is here to stay because both the birds and the mosquitoes are the reservoirs of the disease agent (virus). Pathogens & Parasites Insects transmit a wide variety of parasites and pathogens, including viruses, bacteria, Protozoa, and filarial worms. Bacteria are a diverse group of single celled organisms that do not have a nuclear membrane. Belong to the Kingdom Eubacteria. Bacterial diseases are generally treatable with antibiotics. Vaccines have been developed for only a few bacterial diseases.
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ch21 - ENT 100 Fall 2009 1 Lecture 21 Insects Disease Many...

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