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Understanding Parasites & Their Impact on Human Health: Clinical Parasitology, Study notes of Parasitology

Southwestern University (SWU)Parasitology

A comprehensive study of parasites, their hosts, and the relationship between them, with a focus on parasites of human significance and their medical implications. It covers topics such as clinically significant parasites, tropical medicine, disease and tropical diseases, types of parasites, hosts, and vectors, as well as the life cycle of parasites and methods of transmission. The document also discusses the impact of parasites on human health and potential strategies for morbidity control and environmental management.

Typology: Study notes

2023/2024

Uploaded on 03/31/2024

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CLINICAL PARASITOLOGY
INTRODUCTION TO
PARASITOLOGY
2BSMLS-B1 | DY, JEANNE ARA CLAIRE 1
I. INTRODUCTION.
PARASITOLOGY.
is the area of biology concerned with the
phenomenon of dependence of one living
organism on another.
a study of parasites, their hosts, and the
relationship between them
Clinical (Medical) Parasitology
is concerned primarily with parasites of humans
and their medical significance, as well as their
importance in human communities
Clinically Significant Parasites
are parasites that post infection/harm to the
human host
are commonly isolated in the laboratory
Tropical Medicine
is a branch of medicine that deals with tropical
diseases and other special medical problems of
tropical regions
Disease
is the clinical manifestation of the infection
shows the active presence and replication of the
parasite causing damage to the host
may be mild, severe and fulminant and in some
cases may even cause death of the host
Tropical Disease
is an illness, which is indigenous to or endemic
in a tropical area but may also occur in sporadic
or epidemic proportions in areas that are not
tropical. Many tropical diseases are parasitic
diseases.
Incidence
a happening/period of new cases in a total
population in a specified period
Prevalence
how rampant/widespread the infection is
Reservoir
is the source of infection
could also transmit infection
Tropical Disease
carries and has the disease but does not
show/manifest clinical signs & symptoms
vehicle of the disease
Ex. Mary Mallon - first person to have a carrier
state of disease, had salmonella without any
symptoms
Pre-Patent Period/Biological Incubation Period
a measure of two periods of time (initial
exposure to the manifestation of symptoms)
the time between the initial exposure to the
detection/diagnosis of the parasite on the
clinical specimen
Extrinsic Incubation Period
interval between the entry of the parasite into
the vector and the time it takes to become
capable of transmitting the infection
duration required for the complete development
of the pathogen in the intermediate host
Autoinfection
the source of infection is yourself
Types:
1. External autoinfection - oral-fecal
transmission (enterobius)
2. Retroinfection - infection goes back to
the host
3. Internal autoinfection - parasite jumps
from one organ to another (infects other
organs)
Superinfection/Superimposed infection
parasitic load is higher than the initial infection
parasite shows resistance & adaptability
Ex. scolex
- neck of the worm
- considered as the body region of the
helminth
- produces new body for the worm
II. PARASITES.
depends on a living host for their nourishment
and survival
are often described/classified according to their
habitat and mode of living/development
needs a host to survive and get nutrients from
is usually applied to Protozoa (unicellular
organisms) and Helminths (multicellular
organisms)
pf3
pf4
pf5
pf8
pf9
pfa

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INTRODUCTION TO

PARASITOLOGY

I. INTRODUCTION.

PARASITOLOGY.

is the area of biology concerned with the phenomenon of dependence of one living organism on another. a study of parasites, their hosts, and the relationship between them Clinical (Medical) Parasitology is concerned primarily with parasites of humans and their medical significance , as well as their importance in human communities Clinically Significant Parasites are parasites that post infection/harm to the human host are commonly isolated in the laboratory Tropical Medicine is a branch of medicine that deals with tropical diseases and other special medical problems of tropical regions Disease is the clinical manifestation of the infection shows the active presence and replication of the parasite causing damage to the host may be mild, severe and fulminant and in some cases may even cause death of the host Tropical Disease is an illness, which is indigenous to or endemic in a tropical area but may also occur in sporadic or epidemic proportions in areas that are not tropical. Many tropical diseases are parasitic diseases. Incidence a happening/period of new cases in a total population in a specified period Prevalence how rampant/widespread the infection is Reservoir is the source of infection could also transmit infection Tropical Disease carries and has the disease but does not show/manifest clinical signs & symptoms vehicle of the disease Ex. Mary Mallon - first person to have a carrier state of disease, had salmonella without any symptoms Pre-Patent Period/Biological Incubation Period a measure of two periods of time (initial exposure to the manifestation of symptoms) the time between the initial exposure to the detection/diagnosis of the parasite on the clinical specimen Extrinsic Incubation Period interval between the entry of the parasite into the vector and the time it takes to become capable of transmitting the infection duration required for the complete development of the pathogen in the intermediate host Autoinfection the source of infection is yourself Types:

  1. External autoinfection - oral-fecal transmission (enterobius)
  2. Retroinfection - infection goes back to the host
  3. Internal autoinfection - parasite jumps from one organ to another (infects other organs) Superinfection/Superimposed infection parasitic load is higher than the initial infection parasite shows resistance & adaptability Ex. scolex
  • neck of the worm
  • considered as the body region of the helminth
  • produces new body for the worm II. PARASITES. depends on a living host for their nourishment and survival are often described/classified according to their habitat and mode of living/development needs a host to survive and get nutrients from is usually applied to Protozoa (unicellular organisms) and Helminths (multicellular organisms)

INTRODUCTION TO

PARASITOLOGY

PARASITES CAN BE CLASSIFIED AS (ACCORDING TO

HABITAT):

Endoparasite a parasite living inside the body of a host its presence is called an infection Ex. Protozoans, Nematodes, Cestodes, Trematodes Ectoparasite a parasite living outside the body of a host or a parasite found on the host inhabit only the body surface of the host without penetrating the tissue its presence is called an infestation Ex. Tick, Flea, Mites, Fly Free-living Stage nonparasitic stages of active existence is independent of the host Parasitic Stage/Life can’t live outside the host Ubiquitous microorganisms found everywhere TYPES OF PARASITES ENDOPARASITES Obligate Parasite a parasite that needs a host at some stage of their life cycle to complete their development and to propagate their species. cannot exist without a host Ex. tapeworms depend entirely upon their host for existence Facultative Parasite may exist in a free-living state or may become parasitic when the need arises “ can be ” Ex. pathogenic free-living amoebas like: Naegleria fowleri Acanthamoeba sp. Accidental / Incidental Parasite establishes itself in a host where it does not ordinarily live Ex. Toxocara canis : it can live subcutaneously in humans but it will not develop further to the mature form. It will only develop in animals (e.g. dogs & cats) Aberrant / Wandering Parasite cannot live or develop further one that can’t be transmitted from human to human. Ex. Trichinella spiralis : once it goes into the muscles, its further development will stop Erratic Parasite a parasite is considered erratic when it is found in an organ which is not its usual habitat is all over the place same host but different organ Ex. E. histolytica normally invades the large bowel, but in rare instances, it can affect other organs like the brain and liver Ascaris : usually found in the GIT, but if it is found elsewhere then it is an erratic parasite

INTRODUCTION TO

PARASITOLOGY

parasite harbors larval form or parasite replicates asexually if there is more than one intermediate host, these can be classified as first and second intermediate hosts Ex. Pigs or cattle serve as intermediate hosts of Taenia spp ., while snails are hosts of Schistosoma spp. Paratenic Host the source of infection is a transport host the parasite does not develop further to later stages but it remains alive and is able to infect another susceptible host larval stage survives but does not develop further are important because they widen the parasite distribution and bridge the ecological gap between the definitive and intermediate hosts Ex. Paragonimus metacercaria in raw wild boar meat can pass through the intestinal wall of humans and complete its development. In this case, the wild boar serves as a paratenic host transferring the infective stage to humans. Reservoir Host animals that harbor the parasite other than definitive, intermediate, and paratenic hosts they allow the parasite’s life cycle to continue and become additional sources of human infection to a susceptible host Ex. Pigs are reservoirs of Balantidium coli , field rats of Paragonimus westermani , and cats of Brugia malayi. Accidental Host unusual place/organ for the parasite to be found OTHERS Incidental Host an individual that, though infected, is not necessary for the survival or development of the parasite humans may be the most important host in the spread of the disease or an incidental host of parasites prevalent in other animals IV. VECTORS. an agent that is responsible for transmitting the parasite from one host to another usually an arthropod that transmits an infection from man to man or from other animals to man Ex. female Anopheles is the vector of malarial parasite TYPES OF VECTORS Biologic Vector refers to a vector, which not only assists in the transfer of parasites but the parasites undergo development or multiplication in their body as well

INTRODUCTION TO

PARASITOLOGY

also called as true vectors transmits the parasite only after the latter has completed its development within the host is an essential part of the parasite’s life cycle a certain period has to elapse after the parasite enters the vector before it becomes infective Ex.

  1. Mosquito: Malaria, filariasis
  2. Sandflies: Kala-azar
  3. Tsetse flies: Sleeping sickness
  4. Reduviicl bugs: Chagas disease
  5. Ticks: Babesiosis Mechanical / Phoretic Vector assists in the transfer of parasitic form between hosts but is not essential in the life cycle of the parasite only transports the parasite Ex. Flies and cockroaches that feed on fecal material may carry enteric organisms and transfer these to food, which could be ingested by humans. Carrier a person who is infected with the parasite without any clinical or subclinical disease can transmit the parasite to others Self finger-to-mouth transmission, Ex. e.g. pinworm internal reinfection Ex. Strongyloides Fomites found in beddings, pillows, etc. inanimate objects that can transfer infection V. HOST-PARASITE RELATIONSHIPS. TYPES OF SYMBIOSIS Symbiosis both host and parasite are dependent upon each other none of them suffers any harm from the association is the living together of unlike organisms may also involve protection or other advantages to one or both organisms Symbiont
  • organisms living in symbiosis Commensalism relationship between two interdependent microorganisms “eating at the same table” one benefits and the other is unharmed only the parasite derives benefit from the association without causing any injury to the host a commensal is capable of living an independent life also Ex. Entamoeba coli in the intestinal lumen are supplied with

INTRODUCTION TO

PARASITOLOGY

an agent that is responsible for transmitting the parasite from one host to another Carrier a person who is infected with the parasite without any clinical or subclinical disease can transmit the parasite to others Self finger-to-mouth transmission, internal reinfection Arthropods Mosquitoes - are vectors of malaria and filarial parasites. Triatoma bugs - are carriers of Trypanosoma cruzi causing Chagas disease. Sand flies (e.g., Phlebotomus spp.) - are the natural vectors of all types of Leishmania. Cats - are direct sources of Toxoplasma infection, while rats may be infected with Hymenolepis nana. Other animals, whether wild or domesticated, may also harbor parasites. Another Person, Their Beddings and Clothing May be Asymptomatic carriers of Entamoeba histolytica working as food handlers in food establishments may be important sources of infection. Ex. Autoinfection where the infected person himself is the source of infection is seen in the life cycles of Capillaria philippinensis, Enterobius vermicularis, Hymenolepis nana , and Strongyloides stercoralis. VIII. MODES OF TRANSMISSION. MODES OF INFECTION/TRANSMISSION Oral-fecal most common mode of transmission infection is transmitted orally by ingestion of food, water or vegetables contaminated with feces containing the nfective stages of the parasite Ex. cysts of E. histolytica, and ova of Ascaris lumbricoides Skin Penetration infection is transmitted by the penetration of the larval forms of the parasite through unbroken skin Ex. filariform larva of Strongyloides stercoralis and hookworm can penetrate through the skin of an individual walking bare- footed over fecally contaminated soil) introduction of the parasites through blood- sucking insect vectors Ex. Plasmodium species, Leishmania species and Wuchereria bancrofti Arthropods transmit parasites either by injection into the blood stream of the host directly via their salivary glands, or by forcing parasites into a pool of blood which develops when chewing the skin Ex. mosquitoes, fleas, sand flies, lice, fleas, ticks and mites Congenital Transmission vertically transmitted from mother to fetus during pregnancy, birth, or breastfeeding Ex. toxoplasmosis, HIV, hepatitis B, syphilis, chagas, rubella, cytomegalovirus, and herpes simplex virus (TORCH) Direct may be transmitted by

INTRODUCTION TO

PARASITOLOGY

Transmission person-to-person contact in some cases, Ex. by kissing in the case of gingival amebae and by sexual intercourse in trichomoniasis Iatrogenic Transmission caused by health practitioners is seen in case of transfusion malaria and toxoplasmosis after organ transplantation Normal Flora/Normal Microbiota

  • microorganisms that live in harmony
  • opportunistic pathogens
  • will become harmful if the host is immunocompromised IX. PATHOGENS OF PARASITIC DISEASE. Acute Infection SS = severe and sudden Chronic Infection indefinite cannot tell if the disease is severe or mild Subacute intermediate of acute and chronic Latent / Dormant inactive will be active once host is immunocompromised Mechanical Trauma deposition of eggs and migration of larvae and adult worms can cause mechanical irritation Eggs: Trematode eggs being large in size, can be deposited inside the intestinal mucosa (Schistosoma mansoni), bladder (Schistosoma haematobium), lungs (Paragonimus), liver (Fasciola hepatica) and can cause mechanical irritation Larvae: Migration of several helminthic larvae (hookworms, Strongyloides or Ascaris) in the lungs produce traumatic damage of the pulmonary capillaries leading to pneumonitis Adult worms: Adult worms of hookworm, Strongyloides, Ascaris or Taenia get adhere to the intestinal wall and cause mechanical trauma Necrosis death of a certain tissue Space Occupying Lesions may cause compress the surrounding tissues or organs Ex. hydatid cysts and neurocysticercosis Inflammatory Reactions most of the parasites induce cellular proliferation and infiltration at the site of their multiplication Ex. E. histolytica provokes inflammation of the large intestine leading to the formation of amoebic granuloma Adult worm of W. bancrofti causes mechanical blockage and chronic inflammation of the lymphatics and lymph vessels Trematode eggs can induce inflammatory changes (granuloma formation) surrounding the area of egg deposition Enzyme production and lytic necrosis obligate intracellular parasites of man (Plasmodium, Leishmania and Trypanosoma) produce several enzymes, which cause digestion and necrosis of host cells Ex. E. histolytica produces various enzymes like cysteine proteinases, hydrolytic enzymes and amoebic pore forming proteins that lead to destruction of the target tissue Toxins may be responsible for pathogenesis of the disease Ex. E. histolytica. in contrast to bacterial toxin, parasitic toxins have minimal role in pathogenesis Allergic manifestations metabolic and excretory products of the parasites get absorbed in the circulation and

INTRODUCTION TO

PARASITOLOGY

helminth eggs excreted in feces. The latter is expressed as the number of eggs per gram (epg). Morbidity clinical consequences of infections or diseases that affect an individual’s well-being TREATMENT. Deworming the use of anthelminthic drugs in an individual or a public health program Cure rate the number (usually expressed as a percentage) of previously positive subjects found to be egg negative on examination of a stool or urine sample using a standard procedure at a set time after deworming Egg reduction rate (ERR) the percentage fall in egg counts after deworming based on examination of a stool or urine sample using a standard procedure at a set time after the treatment Selective treatment treatment involves individual-level deworming with selection for treatment based on a diagnosis of infection or an assessment of the intensity of infection, or based on presumptive grounds this can be used in whole populations, or in defined risk groups Targeted treatment group-level deworming the (risk) group to be treated (without prior diagnosis) may be defined by age, sex, or other social characteristics irrespective of infection status Universal treatment population-level deworming the community is treated irrespective of age, sex, infection status, or other social characteristics Preventive Chemotherapy the regular, systematic, large-scale intervention involvies the administration of one or more drugs to selected population groups aims of reducing morbidity and transmission of selected helminth infections Coverage to the proportion of the target population reached by an intervention Efficacy the effect of a drug against an infective agent in ideal experimental conditions and isolated from any context Effectiveness a measure of the effect of a drug against an infective agent in a particular host, living in a particular environment with specific ecological, immunological, and epidemiological determinants. usually measured through qualitative and quantitative diagnostic tests Drug resistance a genetically transmitted loss of susceptibility to a drug in a parasite population that was previously sensitive to the appropriate therapeutic dose PREVENTION AND CONTROL. Morbidity control the avoidance of illness caused by infections may be achieved by periodically deworming individuals or groups, known to be at risk of morbidity Information-education-communication (IEC) is a health education strategy that aims to encourage people to adapt and maintain healthy life practices Environmental management the planning, organization, performance, and monitoring of activities for the modification and/or manipulation of environmental factors to preventing or minimizing vector or intermediate host propagation and reducing contact between humans and the infective agent Environmental sanitation

INTRODUCTION TO

PARASITOLOGY

involves interventions to reduce environmental health risks including the safe disposal and hygienic management of human and animal excreta, refuse, and waste water also involves the control of vectors, intermediate hosts, and reservoirs of disease covers the provision of safe drinking water and food safety; housing that is adequate in terms of location, quality of shelter, and indoor living conditions; facilities for personal and domestic hygiene; as well as safe and healthy working conditions Sanitation providing access to adequate facilities for safe disposal of human excreta and access to safe drinking water ERADICATION VERSUS ELIMINATION. Disease eradication defined as a permanent reduction to zero of the worldwide incidence of infection caused by a specific agent, as a result of deliberate efforts continued measures are no longer needed once this is achieved Disease elimination is a reduction to zero of the incidence of a specified disease in a defined geographic area as a result of deliberate efforts continued intervention or surveillance measures are still required