HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I.Fedoniuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCENOTIC LEVEL OF ORGANIZATION OF LIFE AND THE PLACE OF HUMAN IN IT

2.2. BIOLOGICAL FOUNDATIONS OF PARASITISM AND PARASITIC DISEASES IN HUMANS

Parasitism is a form of antagonistic coexistence between organisms of different species, in which one (the parasite) uses the other (the host) as a source of Nutrition and habitat, causing harm to the host, though usually not enough to cause its death. The phenomenon of parasitism is extremely widespread in nature. Parasitic forms include all Viruses, many Bacteria, Fungi, animals, and some plants.

Parasitology (from Greek parasitos – parasite, logos – science) is the science that studies the phenomenon of parasitism, the biology and ecology of parasites, the diseases they cause, and Methods of their control. Medical parasitology studies these same issues with respect to The Human Body. It consists of three main branches: 1) medical protozoology; 2) medical helminthology; and 3) medical arachnoentomology. Medical protozoology studies human parasites from the subkingdom Protozoa; medical helminthology investigates parasitic worms (helminths) of humans; medical arachnoentomology focuses on Representatives of the phylum Arthropoda that are of medical significance.

Classification of parasites. Depending on their localization, parasites are divided into ectoparasites and endoparasites. Ectoparasites (external parasites) live On the surface of the host's body (Skin, Hair). For example, lice. Endoparasites (internal parasites) live within the Internal Organs, Tissues, cavities, or Cells of the host's body (e.g., dysenteric ameba, Ascaris). Depending on the duration of contact with the host, parasites can be temporary or permanent. Temporary parasites are typically associated with the host only during feeding and spend most of their Life in the external environment (e.g., mosquitoes, argasid ticks). Permanent parasites are subdivided into relatively permanent (which spend only a certain stage of their development on the host) and obligately permanent, which spend their entire life on or inside the host and cannot survive in the external environment at any stage of their development (e.g., malaria plasmodia, lice). Some parasites (monoxenous) are adapted to life in a single host species (e.g., the human roundworm parasitizes humans exclusively), while others (heteroxenous) inhabit multiple species (e.g., Trichinella is a parasite of over 100 mammal species).

Classification of hosts. Hosts are categorized as definitive, intermediate, and reservoir. A definitive (final) host is an Organism in which the parasite reaches sexual maturity and reproduces sexually. An intermediate host is an organism in which the parasite resides in a larval stage or reproduces asexually. If There are two intermediate hosts, the second one is called supplementary. A reservoir host is an organism in which the parasite maintains its viability and accumulates without undergoing further development.

A parasitic system is a parasite population together with all host populations that directly support its existence.

Interactions in the parasite-host system. Pathogenicity is the potential ability of a given parasite species to cause an invasive process or parasitic disease. Pathogenicity is a specific trait, meaning a given parasite causes only a specific parasitic disease (e.g., the whipworm causes trichuriasis). An invasive process is the totality of all defense and pathological Reactions of the organism that arise in response to the penetration and action of a parasite. Virulence is the degree of pathogenicity. An invasive (parasitic) disease is the extreme stage of Development of the invasive process, manifested by specific clinical signs. The impact of the parasite on the host is mechanical and toxic, and involves feeding at the host's expense. The extensiveness of invasion is the relative number of individuals in a population infected by the parasite. The intensity of invasion is the number of parasites in a single individual, organ, or Cell.

The host responds to the invasion of a parasite with a complex of defense mechanisms. It has been established that a parasitic disease does not always develop. Susceptibility to infection is influenced by age, physiological state, and the condition of The Immune System. The host's impact on the parasite includes cellular, tissue, and humoral reactions. The host organism serves as a first-order environment for the parasite (according to E.N. Pavlovsky). The external environment in which the host lives is the second-order environment. The external environment affects the parasite through biotic and abiotic factors not directly, but through the host organism.

Different species of parasites can coexist within a host organism. The collection of parasites simultaneously living in a host organism or in its individual organs is called a parasitocenosis, a term proposed by E.N. Pavlovsky (1952). Parasites of different species enter into certain interactions with each other, enhancing or weakening their combined harmful effect on the host organism. For instance, bacterial dysentery in patients suffering from ascariasis and other helminthiases runs a more severe course and is harder to treat. It is important for a pharmacist to understand these interrelationships within parasitocenoses. The entire complex of organisms (parasites and non-parasites) together with the host organism was termed a symbiogeocenosis by the Ukrainian parasitologist O.P. Markevych.

Morphophysiological adaptations to parasitism: 1) presence of fixation organs in parasites (suckers, hooks, attachment grooves); 2) enlargement of the Digestive System through The Development of blind intestinal caeca (e.g., medicinal leech, ticks); 3) high fecundity due to the extensive development of the Reproductive System; 4) simplification of body Organization through the reduction or loss of certain organs (e.g., absence of locomotion organs and digestive system in tapeworms, loss of wings in lice and fleas).

The life cycle of a parasite is the set of developmental stages through which the parasite reaches sexual maturity and becomes capable of initiating the next generation. A parasite carrier is a human or animal in whose body parasites live without causing clinical manifestations of the disease. The source of the infectious agent (parasite) is the organism that serves as its natural habitat and site of reproduction. This is

a peculiar reservoir where the natural accumulation of pathogens takes place, from which they can be released to infect a susceptible human or animal (L.V. Hromashevsky). The Mechanism of pathogen transmission (how parasites enter the host organism) is the way by which the pathogen moves from an infected organism to a susceptible one. The MAIN MECHANISMS OF pathogen transmission are:

1) fecal-oral (alimentary, if food is the transmission factor); 2) vector-borne (transmissive); 3) contact. Autoinfection involves developing within the host organism without passing through the external environment. Reinfection is a reinoculation of a person with parasites by which they were previously infected and subsequently recovered or suffered. Autoreinfection is a form of self-infection where a person is reinfected by their own parasites.

Classification of diseases. There is a large group of diseases caused by living organisms, known as infectious and parasitic diseases. They are divided into infectious and invasive (parasitic) diseases. Infectious diseases are caused by non-animal organisms—viruses, bacteria, rickettsia, fungi; invasive or parasitic diseases (parasitoses) are caused by animal organisms: protozoa, parasitic worms, Arthropods. The names of parasitic diseases are formed by adding suffixes such as "-iasis", "-osis", or "-esis" to the Base of the species (or genus) name (e.g., amebiasis, trichinosis, Scabies). Both infectious and invasive diseases are subdivided into anthroponoses and zoonoses. Anthroponoses are diseases specific exclusively to humans (e.g., amebiasis). Zoonoses (anthropozoonoses, zooanthroponoses) are diseases whose pathogens affect both animals and humans (e.g., leishmaniasis, echinococcosis).

Vector-borne (transmissive) diseases. The pathogens of vector-borne diseases, both infectious and invasive, are transmitted from one host to another via vectors. Vector-borne diseases are divided into obligately transmissive and facultatively transmissive. Pathogens of obligately transmissive diseases are transmitted exclusively through vectors (e.g., malaria, epidemic and relapsing fevers). Pathogens of facultatively transmissive diseases can be transmitted both via vectors and through other routes (e.g., plague, tularemia). The plague pathogen can be transmitted to humans transmissively (via flea bites), as well as through contact (when skinning infected commercial rodents) or airborne droplets (in pneumonic plague). Vectors can be specific or mechanical. Specific (obligate) vectors are those in whose bodies the pathogen undergoes a developmental cycle. These are predominantly Blood-sucking arthropods; for example, the Anopheles mosquito is a specific vector of the malaria parasite. In the bodies of mechanical vectors, the pathogen does not undergo a developmental cycle but is merely transported spatially. For instance, pathogens of various diseases can be found on the body surface, feet, or in the intestine of the housefly.

Natural focal diseases are infectious and invasive diseases that can persist for a long time in specific geographical areas independently of humans. The Doctrine of natural foci of diseases was developed in the 1930s by Academician E.N. Pavlovsky. A natural focus is an area of land with a specific biocenosis, the mandatory components of which are: 1) the disease pathogen; 2) the natural reservoir of the pathogen (wild animals); 3) the vector of the pathogen. A natural focus is potentially dangerous to humans. If a person enters its territory (during expeditions or hunting), they can contract the pathogen. Initially, natural focality was established for vector-borne diseases: taiga (spring-summer) encephalitis, tick-borne relapsing fever, leishmaniasis. Later, it was discovered that non-vector-borne diseases, including helminthiases (opisthorchiasis, paragonimiasis, diphyllobothriasis, trichinosis, alveolar echinococcosis), are also naturally focal. In addition to natural foci, there are synanthropic (rural, village, urban) and natural-synanthropic foci of invasive and infectious diseases. The doctrine of natural focality is included in WHO control programs for parasitic diseases. When developing such measures, the biological CHARACTERISTICS OF THE pathogen, vector, and reservoir animals are taken into account.

Parasitic diseases (parasitoses) are among the most widespread pathologies. According to WHO data, the number of people suffering from ascariasis worldwide reaches 1 billion. Ancylostomiases rank second with 900 million cases, and in certain foci, up to 90% of the population is infected. Trichuriasis (500 million cases), amebiasis (400 million), giardiasis (370 million), and enterobiasis (350 million) are prevalent almost everywhere.

Prevention of parasitic diseases. Preventive measures are guided by the following directions: 1) direct or indirect elimination of parasites and their germs in the environment and the human body; 2) prevention of human infection by specific parasites; 3) raising general sanitary culture.

Preventive measures must be backed by precise knowledge of: 1) human parasite fauna; 2) parasite biology and living conditions (ecology); 3) the reciprocal impacts between the parasite and the host organism; 4) the effects of medications on parasites; 5) the transmission routes of parasitic disease agents.

Methods of preventing parasitic diseases include biological, immunological, ecological, and social approaches. Biological methods involve using other organisms to combat parasites and their vectors. For example, Gambusia fish are used to destroy malaria mosquito larvae. Immunological methods for preventing human parasitic diseases are insufficiently developed. Ecological methods involve protecting the environment from contamination with invasive parasite stages (e.g., from human feces containing protozoan cysts or helminth eggs). Social methods of prevention encompass therapeutic, sanitary, and hygienic measures: detection and Treatment of patients, organization of sanitary supervision over Water supply sources and food preparation technology, and veterinary-sanitary inspection. The effectiveness of preventive measures largely depends on public participation and compliance with personal hygiene rules.