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Jaramogi Oginga Odinga University of Science and Technology
General parasitology
Unit code: AAS3212
Malaria.
i) Causative agents
Malaria is caused by a single protozoan parasite of genus plasmodium. There are four types of species
which infect human, Plasmodium falciparum, Plasmodium vivax, plasmodium malariae and Plasmodium
ovale.
ii) Morphology of causative agent
These parasites are transmitted to vertebrate hosts by insect’s vectors. In vertebrates, they form
amorphous developmental stages in blood cells. All stages have a reduced apical complex (lacking a
canoid). Plasmodium undergoes exoerythrocytic schizogony in hepatocytes of vertebrates, and then
repeated cycles of intraerythrocytic schizogony with some stages undergoing gametogony. Many species
produce haemozoin pigment granules as a byproduct of hemoglobin metabolism.
Gametes ingested by insect vectors undergo fertilization in gut forming motile zygotes which form
oocysts on the outer gut wall. The oocysts produce thousands of sporozoites which infect the salivary
glands and are injected into vertebrate hosts during feeding.
Life cycle of causative agents
In humans, the parasites grow and multiply first in liver cells and then in red cells of the blood. In the
blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter
parasites (merozoites) that continue the cycle by invading other red cells.The blood stage parasite (which
cause symptoms of malaria) are ingested during blood feeding by a female Anopheles mosquito, they
mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito.
After 10-18 days, a form of a parasite called a sporozoite migrates to the salivary glands of mosquito.
When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected
together with sporozoites, which migrate to the liver, thereby beginning a new cycle.
Clinical signs and treatment of malaria
Symptoms include fever and flu-like illness, including shaking chills, headache, muscles aches and
tiredness. Nausea, vomiting and diarrhea may also occur. Malaria may cause anemia and jaundice. In
animals, malaria can spread heartworm in cats and dogs.
Treatment
Sensitive animals like puppies should be housed in closed or screened buildings and mosquito inside
killed with insecticides. Imidacloprid can be used to dogs to repel female mosquitos’ up to 4 weeks.
Humans should take antimalarial drugs when visiting places which are prone to mosquitoes.
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Toxoplasmosis
Causative agent
Toxoplasma gondii is a protozoan parasite that infects most species of warm blooded animals and causes
the disease toxoplasmosis.
Morphology of causative agents
There are three infectious stages of the parasite with morphological stages that allow them to
survive and multiply in the cells of the host.
Tachyzoites
They often multiply in various cells of the host. They are characterized by a pointed anterior
region and rounded posterior giving them a somewhat comma shaped appearance. Also they
contain a number of organelles that include apical rings, pellicle, polar rings, rhoptries,
micropore and nucleus among other organelles found in eukaryotic cells. Tachyzoites lack
specialized structures as cilia and flagella used for locomotion however, they can glide, extend,
retract and rotate as they search for the host cells. Tachyzoites are surrounded by a
parasitophorous vacuole followed by development of a tubulovesicular membrane network
within the vacuole. They divide asexually through a process known as endodyogeny.
Bradyzoites
They are also known as cystozoites and they multiply within the tissue of the host. They are
characterized by a spherical or ovoid cells surrounded by a thin cyst wall. However, they may
also appear more slender in shape. Their nucleus are located at the posterior end. Like
tachyzoites, bradyzoites multiply through endodyogeny.
Sporozoites
Sporozoites contain a high abundance of granules in the micronemes, rhopties, and amylopectin.
Sporozoites are similar to tachyzoites in size. Some of cell organelles that can be found in
sporozoites are; Golgi complex in the sub terminal nucleus, centrioles, apicoplast, microneme,
endoplasmic reticulum. Sporozoites within the oocysts are protected from various harsh
conditions by the oocyst wall. Following ingestion, this wall is degraded allowing the
sporozoites to be released.
Life cycle of causative agent
The only known definitive hosts for Toxoplasma gondii are members of family Felidae
(domestic cats and their relatives). Unsporulated oocysts are shed in the cat’s feces. Oocysts take
1-5 days to sporulate in the environment and become infective. Intermediate hosts in nature
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(including birds and rodents) become infected after ingesting soil, water or plant material
contaminated with the oocysts. Oocysts transform into tachyzoites shortly after ingestion. These
tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites. Cats
become infected directly by ingestion of sporulated oocysts. Animals bred for human
consumption and wild game may also become infected with tissue cysts after ingestion of
sporulated oocysts in the environment.
Human can become infected by eating undercooked meat of animal harboring tissue cysts,
consuming food or water contaminated with cat feces or contaminated environmental samples,
blood transfusion or organ transplant or transplacentally from mother to fetus. In the human host,
the parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain and eyes.
These cysts may remain throughout the life of the host.
Clinical signs and treatment
Most common symptoms of toxoplasmosis include fever, loss of appetite and lethargy. In the
lungs, T.gondii infection can lead to pneumonia which causes difficulty in breathing, in liver
may cause jaudince and also it can affect the eyes and central nervous system, producing
inflammation of the uvea or the uveitis, the retina and the cornea, abnormal pupil size and
responsiveness to light, blindness, lack of coordination, heightened sensitivity to touch,
personality changes, circling and swallowing food, seizures and loss of control over urination
and defecation.
The best approach of treatment is prevention by avoiding exposure. However, people with
weakened immune systems should use preventive medication which include anti-parasite,
chemotherapy protective drugs, antibiotics and antifungal.
Ehrlichiosis
Causative agent
This is a disease caused by oblingate intracellular bacteria of genus Ehrlichia. There are different
species that causes ehrlichiosis. They include Ehrlichia chanffeensis, Ehrlichia muris, Ehrlichia
canis and Ehrlichia ewingii. Dogs are mostly common infected by Ehrlichia canis.
Morphology of causative agent
Life cycle of causative agent
Once the organism has been transmitted, there are three clinical phases of Ehrlichiosis: acute,
subclinical and chronic phase. The acute phase begins after incubation of 8-20 days and lasts for
2-4 weeks, during which the period the organism multiply in reticuloendothelial cells,
lymphocytes and monocytes. Infected mononuclear cells marginate in the small vessels or
migrate into the endothelial tissues or vasculitis ensues. Immunologic and inflammatory
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mechanisms are involved with increased platelet consumption. Platelet associated IgG and
antibodies that recognize protein platelet in dogs with E.canis may play a major role in the
thrombocytopenia. The acute phase usually resolves spontaneously.
The subclinical phase can persist for years. Immunocompetent dogs may be able to eliminate
E.canishowever, the organism persists intracellular in most dogs leading to chronic phase. This
phase can be mild or severe. In mild form, there is vague illness and weight loss. Bone marrow
hypoplasia leading to pancytopenia occurs in severe chronic form. Severity of disease depends
on the age of the dog (young ones more susceptible), strain of the organism, the presence of the
concurrent disease and breed (Germany shepherds are more likely to be infected).
Clinical signs and treatment
During acute phase dogs infected by Ehrlichiosis show signs like: fever, oculonasal discharge,
anorexia, weight loss, dyspnea and lymphadenopathy. Clinical signs seen during chronic phase
are: depression, weight loss, pale mucous membrane, abdominal pain, hemorrhage,
lymphadenopathy, splenomegaly, dyspnea, increased lung sounds, hepatomegaly, arrhythmias,
pulse deficits, polyuria, polydipsia and stiff, swollen, painful joints. Ocular abnormalities such as
perivascular retinitis hyphemia, retinal detachment, anterior or posterior uveitis and corneal
edema may occur. Abnormalities of CNS, including meningeal pain, paresis, cranial nerve
deficits and seizures have been reported.
Treatment of ehrlichiosis is through administration of antibiotic doxycycline in early stages to
prevent severe illness and death

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Jaramogi Oginga Odinga University of Science and Technology General parasitology Unit code: AAS3212 Malaria. i) Causative agents Malaria is caused by a single protozoan parasite of genus plasmodium. There are four types of species which infect human, Plasmodium falciparum, Plasmodium vivax, plasmodium malariae and Plasmodium ovale. ii) Morphology of causative agent These parasites are transmitted to vertebrate hosts by insect’s vectors. In vertebrates, they form amorphous developmental stages in blood cells. All stages have a reduced apical complex (lacking a canoid). Plasmodium undergoes exoerythrocytic schizogony in hepatocytes of vertebrates, and then repeated cycles of intraerythrocytic schizogony with some stages undergoing gametogony. Many species produce haemozoin pigment granules as a byproduct of hemoglobin metabolism. Gametes ingested by insect vectors undergo fertilization in gut forming motile zygotes which form oocysts on the outer gut wall. The oocysts produce thousands of sporozoites which infect the salivary glands and are injected into vertebrate hosts during feeding. Life cycle of causative agents In humans, the parasites grow and multiply first in liver cells and then in red cells of the blood. In the blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter parasites (merozoites) that continue the cycle by invading other red cells.The blood stage parasite (which cause symptoms of malaria) are ingested during blood feeding by a female Anopheles mosquito, they mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito. After 10-18 days, a form of a parasite called a sporozoite migrates to the salivary glands of mosquito. When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected together with sporozoites, which migrate to the liver, thereby beginning a new cycle. Clinical signs and treatment of malaria Symptoms include fever and flu-like illness, including shaking chills, headache, muscles aches and tiredness. Nausea, vomiting and diarrhea may also occur. Malaria may cause anemia and jaundice. In animals, malaria can spread heartworm in cats and dogs. Treatment Sensitive animals like puppies should be housed in closed or screened buildings and mosquito inside killed with insecticides. Imidacloprid can be used to dogs to repel female mosquitos’ up to 4 weeks. Humans should take antimalarial drugs when visiting places which are prone to mosquitoes. Toxoplasmosis Causative agent Toxoplasma gondii is a protozoan parasite that infects most species of warm blooded animals and causes the disease toxoplasmosis. Morphology of causative agents There are three infectious stages of the parasite with morphological stages that allow them to survive and multiply in the cells of the host. Tachyzoites They often multiply in various cells of the host. They are characterized by a pointed anterior region and rounded posterior giving them a somewhat comma shaped appearance. Also they contain a number of organelles that include apical rings, pellicle, polar rings, rhoptries, micropore and nucleus among other organelles found in eukaryotic cells. Tachyzoites lack specialized structures as cilia and flagella used for locomotion however, they can glide, extend, retract and rotate as they search for the host cells. Tachyzoites are surrounded by a parasitophorous vacuole followed by development of a tubulovesicular membrane network within the vacuole. They divide asexually through a process known as endodyogeny. Bradyzoites They are also known as cystozoites and they multiply within the tissue of the host. They are characterized by a spherical or ovoid cells surrounded by a thin cyst wall. However, they may also appear more slender in shape. Their nucleus are located at the posterior end. Like tachyzoites, bradyzoites multiply through endodyogeny. Sporozoites Sporozoites contain a high abundance of granules in the micronemes, rhopties, and amylopectin. Sporozoites are similar to tachyzoites in size. Some of cell organelles that can be found in sporozoites are; Golgi complex in the sub terminal nucleus, centrioles, apicoplast, microneme, endoplasmic reticulum. Sporozoites within the oocysts are protected from various harsh conditions by the oocyst wall. Following ingestion, this wall is degraded allowing the sporozoites to be released. Life cycle of causative agent The only known definitive hosts for Toxoplasma gondii are members of family Felidae (domestic cats and their relatives). Unsporulated oocysts are shed in the cat’s feces. Oocysts take 1-5 days to sporulate in the environment and become infective. Intermediate hosts in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with the oocysts. Oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites. Cats become infected directly by ingestion of sporulated oocysts. Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment. Human can become infected by eating undercooked meat of animal harboring tissue cysts, consuming food or water contaminated with cat feces or contaminated environmental samples, blood transfusion or organ transplant or transplacentally from mother to fetus. In the human host, the parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain and eyes. These cysts may remain throughout the life of the host. Clinical signs and treatment Most common symptoms of toxoplasmosis include fever, loss of appetite and lethargy. In the lungs, T.gondii infection can lead to pneumonia which causes difficulty in breathing, in liver may cause jaudince and also it can affect the eyes and central nervous system, producing inflammation of the uvea or the uveitis, the retina and the cornea, abnormal pupil size and responsiveness to light, blindness, lack of coordination, heightened sensitivity to touch, personality changes, circling and swallowing food, seizures and loss of control over urination and defecation. The best approach of treatment is prevention by avoiding exposure. However, people with weakened immune systems should use preventive medication which include anti-parasite, chemotherapy protective drugs, antibiotics and antifungal. Ehrlichiosis Causative agent This is a disease caused by oblingate intracellular bacteria of genus Ehrlichia. There are different species that causes ehrlichiosis. They include Ehrlichia chanffeensis, Ehrlichia muris, Ehrlichia canis and Ehrlichia ewingii. Dogs are mostly common infected by Ehrlichia canis. Morphology of causative agent Life cycle of causative agent Once the organism has been transmitted, there are three clinical phases of Ehrlichiosis: acute, subclinical and chronic phase. The acute phase begins after incubation of 8-20 days and lasts for 2-4 weeks, during which the period the organism multiply in reticuloendothelial cells, lymphocytes and monocytes. Infected mononuclear cells marginate in the small vessels or migrate into the endothelial tissues or vasculitis ensues. Immunologic and inflammatory mechanisms are involved with increased platelet consumption. Platelet associated IgG and antibodies that recognize protein platelet in dogs with E.canis may play a major role in the thrombocytopenia. The acute phase usually resolves spontaneously. The subclinical phase can persist for years. Immunocompetent dogs may be able to eliminate E.canishowever, the organism persists intracellular in most dogs leading to chronic phase. This phase can be mild or severe. In mild form, there is vague illness and weight loss. Bone marrow hypoplasia leading to pancytopenia occurs in severe chronic form. Severity of disease depends on the age of the dog (young ones more susceptible), strain of the organism, the presence of the concurrent disease and breed (Germany shepherds are more likely to be infected). Clinical signs and treatment During acute phase dogs infected by Ehrlichiosis show signs like: fever, oculonasal discharge, anorexia, weight loss, dyspnea and lymphadenopathy. Clinical signs seen during chronic phase are: depression, weight loss, pale mucous membrane, abdominal pain, hemorrhage, lymphadenopathy, splenomegaly, dyspnea, increased lung sounds, hepatomegaly, arrhythmias, pulse deficits, polyuria, polydipsia and stiff, swollen, painful joints. Ocular abnormalities such as perivascular retinitis hyphemia, retinal detachment, anterior or posterior uveitis and corneal edema may occur. Abnormalities of CNS, including meningeal pain, paresis, cranial nerve deficits and seizures have been reported. Treatment of ehrlichiosis is through administration of antibiotic doxycycline in early stages to prevent severe illness and death Name: Description: ...
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