Lecture - 2 (1st DDS program)|
PREZENTATION (pdf - password)
THE BASIC PARASITOLOGICAL DEFINITIONS
1. The basic parasitological definitions.
Parasite - is an organism that spends a significant portion of its life „in” or „on” the living host organism.
All parasites can be divided into:
• Ectoparasite - a parasitic organism that lives on the surface of its host;
• Endoparasite - a parasitic organism that lives inside its host;
• Facultative parasite - a parasite in which the adult stages may be free-living or use a host, usually depending on the vagaries of certain environmental conditions;
• Obligate parasite - a parasite which necessarily lives a parasitic existence
• Cosmoplitan parasite - is a word-wide parasite;
• Endemic - normally present in a certain geographic area or part of an area;
• Accidental parasite - a parasite found in other than its normal host;
• Typical parasite - parasite found in normal host for this parasite;
• Monoxenous parasite - a parasite living within a single host species;
• Polyxenous parasite - a parasite that infects many species of hosts, it is characterized by a broad host specificity;
• Homoxenous parasite - a parasite that completes its life in one host;
• Heteroxenous parasite - organism living within more than one host during the life cycle; the parasite has to change the host to complete its life cycle;
• Hyperparasite - a parasite that uses another parasite as a host.
Some definitions are associated with host.
• Host - an organism which harbors and nourishes a parasite;
• Definitive host - a host within which the sexual reproduction or adult stage of a parasite occur;
• Intermediate host - a host within which asexual reproduction or immature stages of a parasite occur;
• Paratenic host - transport host - an organism which serves to transfer a parasites from one host to another, but in which development does not occur. The host does not favor or hinder the parasite in the competition of its life cycle. The paratenic host is an ecological rather than a physiological necessity in transmission. The process of infective larvae passing from one paratenic host to another is defined as paratenesis.
• Zoonosis - infection or disease naturally transmitted between man and other vertebrates;
• Parasitemia - the presence of parasites in the circulating blood;
• Vector - is a organism that transmits a parasite from one host to another. Development in the vector may, or may not, occur. Vectors may be divided into: biological and mechanical. Mechanical vector - is a non-essential disseminator of parasites, in which the parasite does not develop. Biological vector - is an organism essential to development and transmission of a parasite, in which the parasite undergoes development.
2. Transmission (routes of infection):
• direct and indirect;
- by contact (person-to-person, animal-to person - zoonosis);
- by contaminated food and water;
• vectors (explain this term):
- mechanical and biological;
- insects which during blood taking inject parasites to the body of the host;
... Plasmodium sp. (malaria) and Anopheles;
... Leishmania sp. (leishmaniosis) and Phlebotomus;
... Trypanosoma sp. (African sleeping sickness) and tse-tse fly;
- insects which during blood taking do not inject parasites but parasites enter the skin through the bite site;
... Loa loa and Chrysops;
... Wuchereria bancrofti (elephantiasis) and Culex;
... Onchocerca volvulus and Simulium;
- during blood sucking vector excretes parasite with stool onto the skin of the host and parasites enter the skin through the skin damage;
... Trypanosoma cruzi (Chagas disease) and Triatoma
• active transmission (penetration through the skin of host);
Schistosoma sp. (fluke)
• other (inhalation, aspiration, transfusion, transplantation)