malaria parasites

The genus plasmodium contains 4 human species:-
1- Plasmodium falciparum.
2- Plasmodium vivax.
3- Plasmodium malariae.
4- Plasmodium ovale.
Geographical distribution
Tropical and subtropical areas
Life cycle
- Habitat: Early after infection the Plasmodium inhabits the liver cells for a certain time, then later it inhabits the red blood cells of the host.
- Vector: Females of Anopheles mosquitoes.
Reservoir host: Humans are the only important reservoir of human malaria
Infective stage: Sporozoites in the saliva of infected mosquitoes.
- Mode of infection:
Inoculation of sporozoites by infective female mosquitoes.

Transmission of infected RBCs during blood transfusion or by contaminated needles and syringes.
Infectivity of blood donors:
- Plasmodium falciparum: for one year.
- Plasmodium vivax and P. ovale for 3 years.
- Plasmodium malariae as long as 50 years.
Pathology
The primary pathologic effects are hemolysis of infected and uninfected R.B.Cs,
The liberation of metabolites of the parasite
The immunologic response of the host to this antigenic material,
The formation of malarial pigment.
In addition, in Falciparum malaria, the parasitized RBCs adhere to the endothelial linings of small blood vessels, so that ischemia consequent upon plugging of the vessels will produce symptoms that vary depending upon organ involved and the degree of tissue anoxia.
Clinical manifestations
- The incubation period range from 6 to 25 days according to the parasite species. In transfusion induced infections, it can be up to 2 months or longer, depending on the number of parasites inoculated.
- Malaria begins by an acute attack and tends to be chronic if not treated.
- Prodromal symptoms often occur 1 to 2 days before an acute attack begins. Finding includes lassitude, myalgia, mild headache, chills, and slight fever.
- Typical malarial paroxysmal febrile attacks show:
1) Cold stage (half to one hour): Sensation of intense cold, shivering with fever.
2) Hot stage (2 -4 hours): fever, up to 410C with hot dry skin.
3) Sweating stage (2-4 hours): Profuse sweating, temperature falls, skin moist and cool.
- Patients also complain from headache, fatigue, dizziness, anorexia, arthralgia, abdominal pain, diarrhea and vomiting. There is anemia, splenomegaly and hepatomegaly.
- Malarial paroxysmal attacks happen again at the following intervals:
a) P. vivax and P. ovale attack occurs every 48 hours (tertian malaria).
b) P. malariae attack occurs every 72 hours (quartan malaria).
c) P. falciparum attack occurs from 24 to 48 hours (malignant malaria).
- In addition to above picture Malignant malaria may be manifested by:
1. Cerebral Malaria: mortality rate is 20% with good medications.
2. Algid malaria: It resembles acute adrenal insufficiently with low blood pressure, collapse and peripheral vascular failure.
3. Gastrointestinal syndromes:
(a) An acute hepatitis, (b) Dysentery(c) Cholera-like, profuse diarrhea watery diarrhea, vomiting, dehydration
4. Pulmonary edema.
5. Black water fever (Malarial haemoglobinuria): The trigger mechanism is irregular dosage of quinine with exposure to cold or exercise.
7. Hypoglycemia
6. Tropical splenomegaly syndrome
a) Massive persistent splenomegaly in individual living in endemic area.
b) A non transient reduction in spleen size upon anti-malarial treatment.
c) Lymphocytic infiltration of the liver.
d) Anemia.
e) Increased serum polyclonal IgM and anti-malarial antibodies and immune complexes.
Diagnosis of malaria
1. Clinical picture
N.B. When any patient who has received a blood transfusion up to 3 months previously develops an unexplained fever, malaria must be suspected.
2. Parasitological examination: Blood film (thin and thick) stained by giemsa or Leishman stains.
3. Provocative test (Ascoli test): By injection of 1/2 cc adrenaline solution 1/1000 subcutaneously to stimulate the parasite to appear in peripheral blood in chronic cases (with no parasites in blood). Also, cold shower may be useful.
4. Serological: IFAT and ELISA may be of value particularly in chronic infection.
Prevention
1. Mosquito control.
2. Treatment of patients.
3. Chemoprophylaxis.