Study guide of medical parasitology. Part 1. Protozoology

50 Pages·2021·4.577 MB·Russian

by  Abdukaeva N. S., Kosenkova N. S., Vasilyeva N. V.

LIBRARY OF PEDIATRIC UNIVERSITY

N.S. ABDUKAEVA, N.S. KOSENKOVA
N.V. VASILYEVA, K.A. FEDYUK
N.V. KHARITONOVA

STUDY GUIDE OF MEDICAL PARASITOLOGY

PART 1
PROTOZOOLOGY

St. Petersburg

0
Ministry N.S. ABDUKAEVA
health care
Russian Federation N.S. KOSENKOVA

N.V. VASILYEVA

K.A. FEDYUK
N.V. KHARITONOVA

STUDY GUIDE
St. Petersburg
State
Pediatric OF MEDICAL
Medical University
PARASITOLOGY

PART 1
PROTOZOOLOGY

Study guide ST. PETERSBURG
2021

1
УДК 576.8
ББК 52.67
У91

У91 Study guide of medical parasitology. Part 1. Protozoology. /
N.S. Abdukaeva, N.S. Kosenkova, N.V. Vasilyeva [et al.]. – SPb.:
SPbGPMU, 2021. – 48 р.

ISBN 978-5-907443-27-3

Study guide of medical parasitology is intended for foreign English-speaking
students. It contains both general and special questions of parasitology. The tutorial is
illustrated by original photographs and diagrams, created by staff of the department
of Medical Biology SPMU. The first part is devoted to protozoan parasites.

Authors: head of the department of medical biology, assistant professor
N.S. Abdukaeva, assistant professor N.S. Kosenkova, senior lecturer N.V. Vasilyeva,
senior lecturer K.A. Fedyuk, senior lecturer N.V. Kharitonova.

Reviewers:
Зав. кафедрой инфекционных заболеваний у детей им. проф.
М.Г. Данилевича ФГБОУ ВО СПбГПМУ МО РФ, профессор, д.м.н.
В.Н.Тимченко
Младший научный сотрудник Зоологического института РАН лаборатории
эволюционной морфологии З.И.Старунова

УДК 576.8
ББК 52.67

Approved by the educational and methodological council of the Federal
state budgetary educational institution "St. Petersburg State Pediatric Medical
University" of the Ministry of Health of the Russian Federation

Produced with the support of the Foundation for Scientific and Educational Initiatives
"Healthy children are the future of the country"

ISBN 978-5-907443-27-3 © SPbGPMU, 2021
2
GENERAL QUESTIONS OF PARASITOLOGY

Parasitism is a form of relations between leaving organisms that is widely spread
in nature. Diseases caused by viruses, bacteria, fungi are called infectious. In contrast
to these invasion diseases are caused by animal parasites, and they are the subject of
our study. The International Classification of Diseases: ICD-10. There are different
kinds of relationship between animals at the fundamental food-seeking or food-
supplying levels, and parasitism is only one of them.
Predation. An animal (predator) may attack another living animal (prey)
consuming part or all of its body for nourishment, killing it in the process, and so
using it as a source of food only once.
Some animals have become so modified that they are unable to obtain food except in
close association, either continuous or at intervals, with members of another species.
Commensalism denotes an association that is beneficial to one partner and gives
nothing (neither good nor bad) to the other. A type of relationship known as
mutualism is observed when such associations are beneficial to both organisms.
Parasitism is a form of antagonistic relations between organisms. One of them is
a parasite. It inhabits the other organism (host) and uses it as a source of food. If a
parasite does not live in a host, it visits a host for nourishment. The important feature
of parasitism is that the host is to some extent injured through the activities of the
parasite. Usually it is a close and prolonged contact that differentiates parasitism from
the predatory activities.
Classification of parasites
Parasites can be classified in different ways.
Classification of parasites according to the life cycle.
 An organism that cannot survive in any other manner is called an obligatory
parasite. Some obligatory parasites are parasitic at one or more stages of their life
cycles but free living at others.
 A facultative parasite is an organism that may exist in a free-living state or, if
opportunity presents itself, may become parasitic.
Classification according to the duration of interaction between a parasite and
a host.
 The temporary parasites contact with their host only during the time
necessary for nutrition.
 The permanent parasites not only use the host as a source of food, but also
for some time live within the host or on the surface of the body.
Classification according to localization of a parasite.
 Those that are found on the surface of the body are called external parasites
(ectoparasites).
3
 Parasites living within the host may be described as internal parasites
(endoparasites).
- Cavity parasites inhabit different cavity connected with external environment.
- Tissue parasites are the dwellers of connective tissue, muscle tissue, nervous
tissue and others.
- Intracellular parasites inhabit cells.
The hosts of the parasites
The host in which parasite riches its sexual maturity and sexual reproduction
occurs is called a definitive host. The species in which larval stages of the parasites
develop (or asexual reproduction occurs) are called intermediate hosts.
Reservoir hosts. Accumulate parasites.

The ways of disease transmission
1. Alimentary-with the food, or drink.
2. Contact way-during the contacts with sick humans or animals, or earth, water,
household articles.
3. Transmissive way- by means of arthropod vectors. If the arthropod is simply
an instrument of passive transfer, we refer to it as a mechanical vector. When the
parasites develop in the vector, the vector is both host and biologic vector (specific
vector).
Vectors can transmit the parasitic agent by means of contamination or inoculation.
The diseases transmitted by vectors are called transmissive diseases.
4. Air-dust way. A low probability for disease agents of animal nature.
The modes of invasion
The agent of a disease can enter the organism of the host in an active or passive
manner. Different ways of invasion are used to enter the organism of the host.
Per os. In this case the invasion occurs via the mouth.
Per cutis. Across the skin.
Across the mucous of different organs: nose eyes and others; through the
placenta (transplacentally).
The stage of invasion, the pathogenic stage
The stage of invasion is a stage of a parasite, that enters the organism of a host,
survives there and begins to develop.
The pathogenic stage is a stage that has a pathogenic effect on the host.

The pathogenic effects
A parasite, by definition, is an organism that to some extent injures its host. Injury
to the host may be brought about in many ways.
 The mechanical effects. Parasite causes physical damage of the host.
4
 Toxic and toxico-allergic effects. The most widespread type of injury is that
brought about by interference with the vital processes of the host through the action
of secretions, excretions, or other products of the parasite
 Deprivation of substances those are necessary for the host.
 Opens the way for secondary infections.
Anthroponosis, anthropozoonosis, zoonosis
A disease that is of humans only is called anthroponosis.
Anthropozoonosis is of both humans and animals. Zoonosis is a disease of
animals.
Diseases with natural centers
Diseases with natural centers have the following characteristic features:
 The circulation of a disease agent takes place in nature without the
participation of humans.
 The reservoir for the agent of a disease are wild animals.
 Local distribution in areas with specific conditions: climate, landscape,
ecosystems.
 The mechanisms that produce the circulation of the disease agents in nature.
5
The Protozoa
The unicellular animal protists, known as the Protozoa, are organized into several
groups, including Amoebozoa (phylum Sarcodina/Rhizopoda), Excavata/
Mastigophora/Flagellata (includes phylum Polymastigina and Kinetoplastida group),
Ciliates (phylum Ciliophora) and Apicomplexans (phylum Sporozoa). Many protists
are free-living, but a few species are pathogenic to humans.
Protists are eukaryotes; their cells provide all functions of an individual organism,
such as locomotion, feeding, excretion, reproduction, etc. That’s why their cells
possess both structures typical for eukaryotic cell (plasma membrane, cytoplasm,
nucleus, cytoskeleton, ribosomes, mitochondria, endoplasmic reticulum, Golgi
complex) and special organelles (for example, food vacuoles for ingesting food and
contractile vacuoles, regulating water balance). Some protists, such as amoebas, are
surrounded only by their plasma membrane. The other protists have a plasma
membrane with an extracellular matrix or other structures. (contain a pellicle).
Mainly protists have one nucleus, but there are some groups with 2 nuclei.
Protists typically reproduce asexually. In addition, some undergo sexual
reproduction regularly, whereas others undergo sexual reproduction at times of stress.
Many protists under unfavorable environmental conditions form cysts with
resistant outer coverings. Cyst is a dormant form in which metabolic processes are
almost completely shut down.
Protists move by diverse mechanisms. The means of locomotion in amoebas are
pseudopods, Flagellata use flagellar rotation and Ciliates have numerous cilia.
Protists can be heterotrophic (phagotrophs or osmotrophs) and autotrophic
(phototrophs) Parasites are heterotrophs. Phagotrophs ingest particles of food by
pulling them into intracellular vesicles called food vacuoles or phagosomes.
Lysosomes fuse with the food vacuoles, introducing hydrolytic enzymes that digest
the food particles within. Digested molecules are absorbed across the vacuolar
membrane.
Protists typically have one nucleus (some of them, as Giardia intestinalis, two
haploid nuclei per cell), but ciliates have two different types of nuclei within their
cells: a small diploid micronucleus and a larger polyploidy macronucleus.
Micronuclei are exchanged during conjugation for sexual reproduction.
Macronucleus provides the daily activities of the organism).
6
PHYLUM CILIOPHORA
CLASS CILIATA

Balantidium coli

Balantidium coli inhabits the large intestine of humans and pigs and causes the
balantidiasis. B.coli occurs in two stages: the trophozoite and cyst. Trophozoites of
Balantidium coli are found in the lumen of colon and feed on bacteria, but also they
may penetrate down into the mucosa, causing ulceration. The trophozoite is
characterized by large numbers of cilia for feeding and locomotion, form vacuoles for
ingesting food (food vacuoles) and regulates water balance (contractile vacuoles), has
two different types of nuclei within the cell: a small micronucleus and a larger
macronucleus. Cyst is the invasive form. A person becomes invaded with
balantidiasis by consumption of food and water contaminated with cysts. In the hosts
digestive tract the cyst wall dissolves and liberates a trophozoite. The patients have
abdominal pains, diarrhea, and blood in the stools. Intoxication results in headache,
weakness.
A person may be infected by Balantidium coli without any symptoms of disease.
Such a person is called cyst-carrier.
Balantidiases may be diagnosed by detecting trophozoite in feces (in diarrhea) or
Balantidium cysts.

A B

Figure 1. Balantidium coli. A – trophozoite, B – cyst.
7
Balantidium coli

Disease. Balantidiases.
Epidemiology. Anthropozoonosis.
Geographical distribution. Worldwide.
Life cycle.

Invasive stage. Cyst.
Mode of invasion/transmission. Per os/ alimentary, ingestion of cysts.
Localization. Large intestine.
Pathogenic stage. Trophozoite.
Pathogenic effect. Toxic effect – the parasite poisons the host by its products of
metabolism and cause the allergy. Mechanical effect – ulceration of the intestinal
wall, feeding on red blood cells (erythrocytes).
Symptoms. Abdominal pain, fever, diarrhea, blood in the stools, headache,
weakness.
Diagnosis. Detecting cysts or trophozoites in feces.
Prevention (prophylaxis). Personal hygiene.
3

1

4

2

А

В
Figure 2. Balantidium coli. A – trophozoite: 1 – cilia, 2 –
macronucleus, 3 – cytostome, 4 – food vacuole; B – cyst.
8
PHYLUM SARCODINA

Entamoeba histolytica

Entamoeba histolytica inhabits mainly the large intestine of humans and causes the
amoebiasis (or amoebic dysentery). The amoebiasis is an anthroponosis. The
trophozoites (the active forms) of E.histolytica move by means of pseudopodia,
cytoplasmic protrusions that may be formed at any point of the cell surface. The
cytoplasm is divided into two layers: ectoplasm and endoplasm. The ectoplasm is
dense and glass-like, it forms the outer layer of the body of the amoebae. The
endoplasm is more liquid, granular. It forms the inner part of the cell and contains the
organoids.
The trophozoites may exist in two living forms: f. minuta and f.magna. F.minuta is
a commensal living in the intestinal lumen. This nonpathogenic form may transform
into the pathogenic f.magna when human immunity is weakened by unfavourable
factors (any disease, over-fatigue). F.magna invades the mucosal crypts where it
forms ulcers. F.magna elaborates a proteolytic enzyme that aids its penetration of the
intestinal mucosa. Ulceration of the intestinal wall is followed by the bleeding.
F.magna may feed on the red blood cells which one can see in phagocytic stomata.
The invading amoebae at times find their way into capillaries to be transported via
the blood stream to the liver or other organs, where abscess formation may occure.
Amoebae that remain in or reenter the lumen of the gut may, if intestinal motility is
rapid, be passed out in liquid or semiformed stools as forma magna. But if motility is
normal they will turn into forma minuta and then enter the resistant cyst stage. Cysts
may be recognized by the presence of a hyaline cyst wall. They are usually spherical
and contain four nuclei. Cysts pass in feces outside the human organism. They may
be ingested with food or water. In large intestine the cyst wall dissolves, nuclei
multiply by mitosis. As a result, eight amoebae form from one cyst.
A person may be invaded by Entamoeba histolytica, but has no symptoms of
disease, because only f.minuta inhabits his intestine. Such a person is called cyst-
carrier.

9