Lecture 1 & 2 Protozoa

Front 1

What are some general features of protozoa?

Back 1

-free living
-can be aquatic or terrestrial
-can by symbionts, commensals or parasites of plants & animals
-microscopic, unicellular eukaryotic organisms

Front 2

What sort of nucleus do protozoa contain?

Back 2

-most protozoa are monokaryotic (having one type of nucleus) except in ciliates which are dikaryotic (macronucleus and micronucleus)
-most non-ciliated protozoa are uninucleate (single nucleus) although some species may be multinucleate (with several nuclei) at some stages of their lifecycle

Front 3

How do protozoa reproduce?

Back 3

-can be asexual (fission, binary, mutiple, shizogony etc.) or sexual (gametogony, syngamy, conjugation)

Front 4

Describe how locomotion is achieved in protozoa.

Back 4

❤Flagella - elongate "whip-like" extensions of the cell membrane (microtubules with 2 + 9 configuration)

❤Pseudopodia - temporary extensions of the cell body or "false feet" (ameboid movement with protoplasmic flow)

❤Cilia - small "hair-like" extensions of the cell membrane (similar in structure to flagella bu with more complicated root system)

❤Undulating membrane - tiny undulatory waves in cell membrane imparting forward gliding motion (mechanism unknown, subpellicular microtubules may be involved)

Front 5

What is a sporozoite, merozoite, trophozoite?

Back 5

❤A sporozoite is the cell form that infects new hosts

❤A merozoite are the result of merogony that takes place within a host cell

❤A trophozoites the activated, intracellular feeding stage in the apicomplexan life cycle. After gorging itself on its host, the trophozoite undergoes schizogony and develops into a schizont, later releasing merozoites.

Front 6

Describe the morphology, hosts, site, lifecycle, pathogenesis, diagnosis & control of the species Eimeria

Back 6

❤Morphology
-one (spoulated) oocyts contains 4 sporocysts containing 2 sporozoites (1-4-2 configuration)

❤Hosts
-most vertebrates, including mammals, marsupials, birds, reptiles, & fish

❤Site:
-most species undergo endogenous development in the intestinal mucosa (small and/or large intestines)
-some species develop in the liver, gallbladder or kidneys
-the parasite undergo several cycles of schizogonogy (=merogony), culminating in mature schizonts (=meronts) lysing host cells to release merozoites
-the parasites then undergo gametogeny, resulting in the formation of non-motile zygotee (ummature oocyst)
-the oocyst undergoes sporogony in the external environement to become a sporolated oocyst containing sporocysts and sporozoites

❤Life cycle:
SCHIZOGONY
-if the infective, sporolated oocyst is ingested by a suitable host, the sporozoites emerge, and each may enter an epithelial or lamina propria cell, round up as a trophozoite, grow larger, and become a first generation schizont
-the trophozoite, schizont, and all other intracellular stages of Eimeria are surrounded by a membrane-lined parasitophorous vacuole in the host cell cytoplasm or, in some cases, nucleoplasm
-this schizont produces first-generation merozoites that burst the cell and invade fresh cells to become second generation schizonts
-there may be several schizogonic generations, but 2-3 are the limit for the most important species of Eimera
-the features of schozogony are:
1) an exponential increase in the number of zoites arising from a single sporozoite
2) destruction of host cells in proportion to the degree of infection
3) automatic suspension of the asexual process after a fixed number of repetitions

GAMETOGONY
-a merozoite produced by the final schizogony (ie. a telomerozoite) enters a fresh host cell and develops into a male or female (microgamont♂ or macrogamon♀t) or developing sex cell
-of the many microgametes formed by the microgametocyte only a small fraction finds and fertilizes macrogametes to form zygotes
-a wall forms around the zygote to form an oocyst

SPOROGONY
-the oocyst is released by rupture of the host cell and passes out with the feces to undergo sporolation
-within a day or two if provided adequate moisture, moderate temperatures, and sufficient oxygen, he single sporont in the oocyst divides into 4 sporoblasts
-each sporoblast develops into a sporocyts, which contains two haploid sporozoites, thus becoming an infective sporolated oocyst and completing the cycle

Front 7

Describe the pathogenesis of the species Eimeria

Back 7

❤Pathogenesis
-certain species are highly pathogenic and cause severe erosion of mucosal membranes through cell lysis, resulting in profuse watery-to-bloody diarrhea
-pathogenicity depends on many factors, such as parasite species, infective dose, reproductive potential, location in tissues as well as host age, nutritional and immune status
-young animals are most susceptible to clinical disease but survivors develop strong specific protective immunity against subsequent infection

Front 8

Describe the diagnosis & control of the species Eimeria

Back 8

❤Diagnosis
-clinical signs can coincide with parasite patency (period during which oocysts are produced)
-infections are usually diagnosed by the coprological examination of host faeces for coccidial oocysts (using floatation techinques)

❤Control
-disease progression is usually rapid, so that curative treatment may be too late
-nonetheless, a broad rage of drugs (coccidiostates: sulphonamies, amprolium, nitrofurans, and pyrimidines) can be used in a preventative and/or curative way
-outbreaks can be controlled (to some extent) by improving hygiene and isolating infected individuals
-vaccines for some Eimeria species (particularly for chickens) are being developed & used

Front 9

What is the significance of Eimeria species?

Back 9

-economy losses - Poultry ****
-enteritis (watery/bloody diarrhea)
-many species - differing virulence
-mostly SI - E. Tenella LI in chickens

Front 10

Describe the morphology, hosts, site, lifecycle, pathogenesis, diagnosis & control of the species Isospora

Back 10

❤Morphology
-one (sporolated) oocyst contains 2 sporocytes each containing 4 sporozoites (1-2-4 configuration)

❤Hosts
-infections occur world-wide, mainly in carnivores (particularly canids & felids) as well as some omnivores (humans, pigs, lizards) and birds (canaries and sparrows)

❤Site
-small intestinal mucosa

❤Lifecycle
-usually direct
-parasites undergo schizogony and gametogony in the intestinal epithelium
-oocysts passed in faeces contaminate the environment and are ingested by specific hosts
-sporulation in the environment
-for some species (e.g. Cystoisospora felis), indirect life cycle possible (e.g. via development of monozoic cysts in mice)

❤Pathogenesis
-most isospora species are only mildly pathogenic but can cause transient diarrhea
-young animals are most susceptible to infection but usually develop a strong protective immunity thereafter

❤Diagnosis
-coprological examination of host faeces for unsporulated oocysts (floatation)

❤Control
-coccidiostats (e.g. sulphonamides) are effective against endogenous life stages
-control by improved hygiene and isolation of infected individuals (which shed high numbers of oocysts)
-give supportive treatment (hydration/electrolytes)

Front 11

Describe the morphology & hosts of cryptosporidium

Back 11

❤Morphology
-endogenous development stage appear as small basophilic bodies attached to the luminal surface of host epithelial cells
-exogenous oocysts have 4 naked sporozoites

❤Hosts
-infections have been detected world-wide in many species of mammals, birds, reptiles & fish
-different parasite species are species are specific for individual vertebrate classes rather than individual host species

Front 12

Describe the site of cryptosporidium

Back 12

❤Site
-most species infect the SMAL INTESTINE of their hose (esp mammals), in birds it's the respiratory tract, and stomach in reptiles
-the parasites are located (intracellularly and extracytoplasmic) within parasitophorous vacoules covered by host microvillous membranes
-they undergo several cycles of schizogony before gamonts are formed
-after fertilization, the oocysts mature and sporulate in the gut, and are usually infective as soon as they are excreted from the host

Front 13

Describe the life cycle of cryptosporidium

Back 13

❤Life cycle
-oocysts excreted by infected hosts contaminate the environment and initiate infections when ingested by susceptible hosts
-some (thin-walled) oocysts are thought to be auto-infective and may excyst in the same host
-oocysts are being detected with increasing frequency in treated and untreated water supplies, and appear to survive most conventional methods of water treatment
-waterborne outbreaks of public health significance (drinking water & swimming pools)
-sometimes food-borne
-infections in domestic mammals have been demonstrated to be zoonotic
-cryptosporidiosis can also be a problem in child day-care centers, and in intensive animal rearing facilities

Front 14

Describe the pathogenesis of cryptosporidium

Back 14

❤Pathogenesis
-infections vary from asymptomatic to mild acute to severe chronic disease
-most clinical infections in immunocompetent individuals involve transient, acute disease, characterised by profuse watery, foul-smelling diarrhoea or acute respiratory signs
-neonates and young individuals are most susceptible, whereas older animal become resistant (immune) to infection
-infections may persist in immunocompromised individuals resulting in protracted chronic disease which may be gastritis (dilation) typified by postprandial regurgitation

Front 15

Describe the diagnosis & control of cryptosporidium

Back 15

❤Diagnosis
-detect oocysts in fecal material or respiratory exudates
-acid fast & stain well with basic fuchsin
-immunological and PCR tests have also been developed
-Cryptosporidium oocysts must be differentiated from Cyclospora cayetanensis
-in cases of severe diarrhea in cats, trichomoniasis should be considered in the list of differential diagnosis

❤Control
-no effective chemotherapeutic agent
-some success with paromomycin & nitazoxanide
-supportive treatment by oral or parenteral rehydration
-some promising results have been obtained by using hyperimmune bovine colostrum for passive immunotherapy
-control measures include identification of the source of the infection, isolation of infected individuals, disinfection of contaminated surfaces, maintaining high standards of hygiene and (for the human population) boiling of water prior to consumption