Introduction to Parasitic Protozoa

• Not classified under Kingdom Animalia but under Kingdom Protista

• Main feature is they are unicellular eukaryotes

• First described some 300 + years ago by Leeuwenhoek when he described Giardia from his own intestine.

Classification

• See Classification beginning on page 49

• Subject to much variation

• Four major types of organisms I will discuss– Flagellated protozoa - Mastigophora– Amoeba - Sarcodina– Ciliated protozoa - Ciliophora– Apicomplexa (sporozoans)

Organelles of Locomotion of Mastigophorans

• Flagella

Organelles of Locomotion of Mastigophorans

• Flagella

Gardia lamblia trophozoite

Microstructure of Cilium9 + 2 configuration

Sarcodina have Pseudopoda

Types of Nutrition

• Autotrophic = Holophytic or photosynthetic

•Zooxanthellae which are found in many Cnidaria and other invertebrates are the best examples of these symbiots.

• Heterotrophic – Holozoic nutrition – Saprozoic nutrition

Reproduction in the Protozoa

• Asexual reproduction – Binary fission – Multiple fission, merogony or

schizogony (also sporogony) – Budding

Reproduction in the Protozoa

• Sexual reproduction – Gametogony– Syngamy

• Isogametes •Anisogametes

Macrogametes - Microgametes -

– Conjugation

Trophozoite or Vegetative Stage

• Entamoeba Giardia lamblia

Encystment

• Entamoeba Giardia lamblia

Protozoa Overview

• Belong to Kingdom Protista

• Unicellular

• Eukaryotic

• Some very important parasites

Family Trypanosomatidae

• Heteroxenous - most members have two phases in the life cycle– first phase, they live in the blood or

tissues of some vertebrate (often called hemoflagellates)

– second phase is found in the gut of some blood sucking invertebrate

• (monoxenous) - have a single host

Forms found in Trypanosomatidae

Trypanosomatidae forms

Forms found in Trypanosomatidae

Genus Trypanosoma

• most important flagellates • divided into two broad sections based

upon development in the invertebrate host– Salivaria - (anterior station development)

These accomodate transmission to vertebrate host during the blood meal of the arthropod.

– Stercoraria Posterior section development. Transmission occurs through fecal contamination

Trypanosoma brucei complex

• Salivaria

• pleomorphic• Vectors are members of the

Tsetse fly (genus Glossina• Live in the blood, lymph nodes and

spleen, and cerebrospinal fluid of the vertebrate host

Glossina

Trypanosoma brucei complex

• Live in the blood, lymph nodes and spleen, and cerebrospinal fluid of the vertebrate host

• Trypanosoma brucei brucei parasite of antelopes and other African ruminants

• pathogenic to domestic ruminants causes nagana a type of sleeping sickness in animals

Trypanosoma brucei gambiense.

• chronic form of African Sleeping Sickness

• west central and central Africa• vectors include Glossina palpalis

and G. tachinoides• Game animals are not reservoir

hosts.

Trypanosoma brucei rhodiense

• acute form of African Sleeping Sickness

• east central and central Africa• Glossina morsitans, G. pallidipes,

and G. swynnertoni are the most important vectors

• Wild game animals are believed to serve as reservoir hosts.

Pathology

• T. gambiense invades the central nervous system initiating a chronic, sleeping-sickness.

• apathy, mental dullness, tremor of hands, tongue, etc. followed by convulsions and paralysis.

• Sleeping follows with coma and death common.

Pathology

• T. rhodiense does not attack the nervous system.

• causes a more rapid death• rapid weight loss, heart

involvement, and death can occur within a few months.

• Winterbottom's sign

Diagnosis and Treatment

• Finding parasites in blood, bone marrow, or cerebrospinal fluid is diagnostic

• Winterbottom’s sign• Today the drug of choice is

difluoromethylorithine (DFMO).

Epidemiology and Control

• attempts to control the tsetse fly vectors.• Vectors of T. brucie and T. rhodiense occur

in open country, pupating in dry, soil• vectors of T. gambiense are riverine flies

breeding in shady, mosit areas along rivers.• Tsetse flies are larviparous • Brush removal is effective (febble flyers)

but must be maintained.

Glossina breeding habitat

Cleared Strips to Control Trypanosoma gambiense

Epidemiology and Control

• Chemical spraying with insecticides

• Elimination of wild game animals .• selective breeding of cattle

Other Salivarian Trypanosomes

• T. evansi Causes a disease in horses, camels, elephants, dogs, and other mammals called surra. Nearly 100% fatality to dogs and elephants if untreated

• can be mechanically transmitted by horseflies

• T. equiperdum no arthropod host. Veneral transmission, it causes dourine in horses.

Stercoraria Trypanosomes

• Trypanosoma cruzi• Chagus discovered the organism in

1910 • Infects cone-nosed bugs belonging to

the family Reduviidae• Causes Chagus disease in humans• Distributed throughout Central and

South America and infects over 19 million people

Vectors of Trypanosoma cruzi

Transmission

• Reduviid bugs usually defecate when they feed

• Feces contains the infective metacyclic trypanosomes.

• These enter the host body when the bite is scratched or mucous membranes

• enter a reticuloendothelial cell of the spleen or liver

Transmission

• Become amasitgote forms and undergo rapid division. Cyst-like pockets of the amastigotes called pseudocyts are formed.

• Amastigotes complete development and enter the blood where they are infective to the insect vector

• Infective metacyclid trypomastigotes appear in the feces within 8 - 10 days.

Pathogenesis of Chagus Disease

• Acute phase - most common in children under 5 years

• Romana's sign• Pseudocysts can form in almost any

tissue Heart muscle ganglion cells are very susceptible and up to 80% of them may be destroyed.

• Death may occur within 3-4 weeks after infection.

Romana’s sign

Pathogenesis of Chagus Disease

• Chronic stage is most often seen in adults.

• May last many years damaging heart muscle ganglion cells.

• In endemic areas, the disease may accont for 70% of the cardiac deaths.

• megaesophagus or megacolon

Pseudocyst of T. cruzi in heart

Epidemiology

• Reduviidae bugs are the most important link to human transmission

• wild mammals may serve as reservoir hosts, dogs and cats are more important reservoirs for human disease.

Epidemiology

• Transmission can also occur through blood transfusions, contaminated needles, transplacental transmission and ? Breast milk

• Thatcched roofs and cracked walls are ideal breeding and hiding places for the bugs

Diagnosis and Treatment

• Presence in the blood, cerebrospinal fluid, fixed tissues or lymph

• Xenodiagnosis is where laboratory reared bugs are allowed to feed on patients and then after a period of time they are examined for flagellates.

• Complement fixation and other immunodiagnostic tests