There are over 100 species of Plasmodium, some of which can infect humans and cause malaria. The four main species that infect humans are P. vivax, P. ovale, P. malariae, and P. falciparum. P. falciparum causes the most severe form of malaria and is responsible for over 1 million deaths per year globally. The life cycle of Plasmodium involves both sexual and asexual reproduction in humans and mosquitoes. Female Anopheles mosquitoes transmit the parasite between humans during blood-feeding. Laboratory diagnosis of malaria is usually done by examining thick and thin blood smears under a microscope to look for the parasite in red blood cells. Treatment depends on the species,

1. PLASMODIUM
WWW.RCVEts.Com

2. Plasmodium
•
•
> 100 species
Both animals and humans
1.
P. vivax  Benign Tertian Malaria
(humans)
2.
P. ovale  Benign Tertian Malaria
(humans)
3.
P. malariae  Benign Quartan Malaria
(humans/chimpanzees)
4.
P. falciparum  Malignant Tertian Malaria (humans)

3. Plasmodia

4. Geographical Distribution
• P. vivax and P. falciparum  more common
P. ovale  rarest of the 4 species
• > 200 million people worldwide
> 1 million deaths per year
Most common lethal infectious disease

5. Geographical Distribution
• Tropical & subtropical areas
esp. Asia, Africa, Central and South America
Certain regions in SE Asia, S. America, E.
Africa  Chloroquine Resistant strains of P.
falciparum

7. HABITAT
• Female Anopheles  sexual cycle
• Liver & RBCs of man  asexual cycle
RBC Age Variable:
 P. vivax  youngest erythrocytes
 P. malariae  oldest erythrocytes
 P. falciparum  RBCs of every age

8. Anopheles, Culex and Aedes aegyptii

10. MORPHOLOGY
•
Peripheral blood stained with Leishman’s stain
1.
Small Trophozoites (Ring forms):
Infected RBC  at first ring form
a)
b)
c)
Dot/rod shaped nucleus (red)
Peripheral rim of cytoplasm (blue)
Central clear vacuole like area (not stained)
Different species have different rings

11. MORPHOLOGY
2.
Large Trophozoite:
•
•
Ring form  Large trophozoite
Fine grains of pigment Hematin
3.
Schizont:
Large trophozoite  schizont  N/C fragments merozoites
4.
Gametocytes:
•
•
•
Male and female distinguishable
Fully grown  rounded  occupies most of RBC
P. falciparum  sausage shaped  crescent in RBC

12. Plasmodia in RBCs

14. LIFE CYCLE
• HOST:
Definitive Host  Female anopheles (sexual cycle)
Intermediate Host  Man (asexual cycle)
• VECTOR:
Female Anopheles

15. LIFE CYCLE
• Sexual cycle initiated in Humans  Gametocytes
(gametogony in RBCs)  mosquitoes 
fusion of M/F gametes  oocyst  many
sporozoites (sporogony)
• Sexual cycle  Sporogony (sporozoites)
• Asexual cycle  Schizogony (schizonts)

16. Detailed Life Cycle

17. Oocysts in Mosquito

19. PATHOGENESIS
• Usual Incubation periods:
Vivax : 14 days
Malariae: 28 days
Falciparum: 11 days
• Transmission:
Mosquito bite
I/V drug abuse
Blood transfusion
Transplacental (congenital)
FEVER, ANEMIA, SPLENOMEGALY

20. PATHOGENESIS
• Malarial Relapses:
• P. vivax  2 years
• Para-erythrocytic stage  liver parenchyma 
dormant but viable
• Resistance lowered  released and activated 
complete erythrocytic cycle
• Not in P. falciparum as no para-erythrocytic stage
• Transmission other than mosquito bites no relapses

21. Natural Protection
• Sickle cell trait (heterozygous)
• Duffy blood group antigen –ve (homozygous
recessive) (P.vivax)
• G6PD deficiency
• Premunition:
• Partial immunity
• Humoral antibodies  block merozoites from
invading RBCs
• Low level of parasitemia low grade symptoms

22. PATHOGENESIS
•
Commonly Involved Organs:
1.
2.
3.
4.
Changes in Blood
Spleen
Liver
Bone Marrow

23. Signs and Symptoms
•
•
•
•
•
•
•
•
•
•
•
Abrupt fever, chills and rigors
Headache
Initially may be continuous then periodic
Upto 41ºC or 106 ºF
Nausea, vomiting, abdominal pain, anorexia, distaste of mouth
Drenching sweats afterwards
Well between febrile episodes
Splenomegaly
1/3 hepatomegaly
Anemia
Falciparum fatal bcz of brain and kidney damage

25. Laboratory Diagnosis
1.
Blood Exam:
a. Microscopic Exam:
•
•
•
•
•
Take blood during pyrexia
Not after even single dose of anti-malarials
Thick and thin smears made, dried and stained
Thick smear  presence of organisms
Thin smear  identification of species

26. Laboratory Diagnosis
• Thin Smear:
•
•
•
•
•
•
Single drop of blood
Spread to allow single cell layer
Leishman’s stain
Oil immersion lens
Ring shaped trophozoites in RBCs
P. falciparum gametocyte banana, sausage or crescent
shaped
• Other species gametocytes are spherical
• > 5 % RBCs infected  Dx of P. falciparum

27. Laboratory Diagnosis
• Thick Smear:
•
•
•
•
•
3-5 drops on slide allowed to dry
Several cell layers thick
Field’s stain or Giemsa stain
Oil immersion lens
Stain removes Hb from RBCs

28. Thin and Thick Smear

29. Laboratory Diagnosis
1.
Blood Exam:
b. TLC and DLC:
•
•
TLC low  leucopenia
In fever may be high
Monocytosis containing pigments

30. Laboratory Diagnosis
2. Biopsy:
•
BM and liver biopsies in difficult cases
3. Therapeutic Test:
•
Anti-malarials given  if fever subsides  Dx made
4. Serological Tests:
•
•
•
•
Fluorescent antibody testing
Complement fixation test
Flocculation test
Hemagglutination test

31. Treatment
 Falciparum easily treated before
complications as no relapses and no paraerythrocytic stage
 Chloroquine is treatment of choice for
sensitive strains of plasmodia (merozoites)
 Primaquine (Hypnozoites)
 Mefloquine or quinine and doxycycline
(chloroquine resistant strains of falciparum)
 Atovaquone and proguanil (Malarone) (CR
falciparum)

32. Prevention
Chemoprophylaxis
Mosquito netting
Window screens
Mosquito repellants
Protective clothing
Special care during night time
DDT or kerosene oil spray over pools of
water
 Drainage of stagnant water
 No vaccine presently available








33. Www.RCVetS.com