Host-Parasite Relationships among Human Protozoa. By ROBERT W. HEGNER, Ph.D. (Professor of Protozoology in the Johns Hopkins School of Hygiene andl. Protozoa are eukaryotic organisms (with a membrane-bound nucleus) which To move from host-to-host, protozoan parasites use one of four main modes of. This chapter discusses the host–parasite relationships of the ciliate protozoa. Every gradation of relationship exists between ciliates and their hosts and.
Typhoid fever b Endemic disease: This term reflects the spread of the disease. Total of cases of disease in a population at any given time. This term reflects how sick the population is. Occurrence of a disease in a population over a defined period of time. When bacteria are actually growing and dividing in the blood.
Commonly felt by the patient. Commonly observed by a physician. Nosocomial infections -- Hospital acquired infections are especially fearsome because: The incubation period - initial infection and the first appearance of signs or symptoms. The prodromal period -short duration. Period of initial mild sign or symptoms. The period of illness -period of maximum presentation of signs and symptoms.
The period of decline -signs and symptoms start to decline. Carrier human -- Inapparent infections, subclinical infection, chronic infection. Zoonosis -- primarily an animal disease and then spread to humans. Examples of diseases with a significant animal reservoir: The encapsulating epithelial cells and fibroblasts of the fluke, Paragonimus westermani in human lungs are transformation of certain other type of cells in the lungs.
This is the growth of cells in a tissue to form a new structure, e. Neoplastic tumour is not inflammatory. This is not required for the repair of organs. It does not conform to a normal growth pattern. It may be benign or malignant.
Endoparasites with a great density causes nutritional deficiency in host by absorbing sugars, vitamins, amino-acids etc. Mal-nourished hosts are more proned to disease and infection. Diphyllobothrium latum a fish tapeworm in human causes anaemia by absorbing profuse Vitamin B12 as much as 10 to 50 times more than do other tape-worms.
Parasites in some cases also feed on host- substances, other than stored or recently acquired nutrients.
Increased number of those adult worms in lymph vessels coupled with aggregation of connective tissue may result in complete blockage of lymph flow. Excess fluid behind the blockage seeps through the walls of lymph ducts into the surrounding tissues, causing edema and ultimately with scar tissues—the elephantiasis of limbs, breasts, scrotum etc.
Effects of toxins, poisons and secretions: Specific poisons or toxins egested, secreted or excreted by parasites cause irritation and damage to hosts, e. Toxin of pathogenic Entamoeba histolytica produces toxic symptoms in parasitized mammalian hosts and creates ulcerations within the large gut of man. Schistosome cercarial dermatitis is the result of an allergin reaction against an irritating parasitic secretion from the fluke.
Gonads of parasitized hosts may change, leading to sex reversals; e. Parasitized male crab acquired secondary female characteristics like broad abdomen, appendages modified to grasp eggs, chelae become smaller, testes with testicular cells at various stages of degeneration.
The mudflat snail—Ilyanassa obsoleta are directly castrated by the trematode— Zoogonus lasius. The freshwater snail, Lymnaea stagnalis is indirectly castrated by larvae Sporocysts of Trichobilharzia ocellata a trematode.
These larvae do not possess mouth and thus destroy the gonadal tissue by chemical means. An interesting aspect of parasite induced change in hosts is responsible for enhanced growth; e.Host-Parasite Relationship
Workers of the ant, Pheidole commutula become much larger when parasitized by the nematode, Mermis sp. Mice infected with larvae of Spirometra mansonoides a tapeworm grows faster than non-parasitized one. Rats when parasitized by Trypanosoma lewise increase their weight more rapidly than non-parasitized one. The enhanced growth of the host is due to stimulation of growth-promoting molecules secreted by the parasites.
In immuno-parasitology, the animal is the host and the parasite is either self by molecular memory or non-self foreign. When a host recognizes the parasite as non-self, it generally reacts against the invader in two ways: Cellular or cell mediated reactions: Where specialised cells become mobilised to arrest and eventually destroy the parasite as usual.
Innate or natural and II. Theoretically each of them again can be of two types—cellular and humoral. Innate internal defense mechanism: These includes the following chief categories: Phagocytosis consists of three phases: Attraction of phagocytes to the non-self material, commonly by chaemo-taxis.
Internalization of the foreign substance i. Fate of phagocytosed parasites: May be degraded intracellularly. May be transported by phagocytes across epithelial borders to the exterior.
May remain undamaged within the phagocytes and some may even multiply within host cells. Fate of encapsulated parasite: Nacrezation is another type of cellular defense mechanism, known in molluscs.
- HOST-PARASITE RELATIONSHIPS OF CERTAIN INTESTINAL PROTOZOA IMPORTANT TO MEDICAL ZOOLOGY
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As certain helminth parasites, e. In so doing, a pearl is formed and the enclosed parasite is killed. The process involves deposition of the black-brown pigment, melanin around the invading parasite.
Melanization is chemically the result of enzymatic oxidation of polyphenol by tyrosinase. This is detrimental to the parasite and may lead to its death by interfering with such vital activities like hatching, moulting or feeding. Melanization of the nematode, Heterotylenchus autumnalis in haemocoel of larval house-fly—Musca domestica.
These fall into two categories: These are two types: Those are directly parasitocidal, e. Those that enhance cellular reactions, e. These glycoprotein molecules enhance phagocytosis of the non-self-material. These are also of two types: Immunity refers to resistance against disease caused by a foreign agent.
Host-Parasite Relationship (With Diagram)
Antigen is the only foreign substance Proteins, glycoproteins, nucleoproteins etc. These are chiefly of two types: Somatic antigens molecules comprising some of parasites. Mechanism of antigen-antibody interactions: Host lymphocytes are now stimulated to proliferate and differentiate.
Plasma cells are B-lymphocyte effector cells that secrete antibodies.
Host-Parasite Relationship (With Diagram)
The parasites try to establish itself within the host while the latter tries to destroy it which results in dynamic state of equilibrium. If resistance is sufficiently high to prevent parasite reproduction, it is known as absolute resistance and if parasite is able to overcome it and still reproducing it is called partial resistance.
The properties and number of antibodies vary from individual to individual parasitic infections. These are known to operate in malaria and other viral reactions by rendering the host cells unfit for habitation by intercellular parasites. Categories of antigen-antibody interactions: These are of three types: This is referred to as agglutination reaction.
Lysin and lysis reaction: Lysin antibodies dissolves or lyses antigens. The reaction occurs in the presence of complement, a substance in normal serum representing a system of enzymes. In the second phase of reaction the fixation of complement by antigen-antibody occurs which is used for detecting many of the parasitological infections. This precipitin reaction is used for detecting infections like plague, anthrax, tularaemia etc.
In vertebrates, this is introduced through the action of antigen, antibody and complement. This occurs in two ways: Opsonins are antibodies occurring in normal as well as in immune sera which inhibit microbes making them more amenable to phagocytosis. This is usually of two types: