Pathological changes in various organs due to malaria

1.. Spleen

i)                    Enlarged spleen

ii)                   Slate grey or black colour .

iii)                 The capsule is thin or thick if it is acute or chronic .

iv)                 Consistency – Soft in acute cases , firm in chronic cases

v)                  Microscopically –

a)      Congested splenic sinusoids .

b)      Haemozoin and haemosiderin are found in abundance .

c)       Malpighian corpuscles are free from pigments and parasites .

d)      Increased macrophage cells .

2.. Liver

i)                    Enlarged liver

ii)                   Dark chocolate red or slate grey or black colour .

iii)                 Dilated lobules

iv)                 Microscopically –

a)      Dialated central veins

b)      Kupffer’s cells are increased .

c)       Fatty degeneration of liver cells .

d)      Parasites are found in red cells .

3.. Bone marrow – There will be little changes in bone marrow of long bones in acute case . In chronic case the upper and lower third of the long bones may be reddish brown in colour , even it may be slate grey or black colour . There will be formation of red formative marro .

      Microscopically –

i)                     Hyperplasia of R.E cell

ii)                   Haemozoin pigment will be present .

iii)                 There will be increased number of nucleated R.B.C and reticulocyte .

iv)                 Malarial parasite is present in R.B.C

4.. Brain - 

a)      The capillaries of brain tissue will distended and may be occluded by the infected R.B.C . This occurs due to pernicious malaria

b)      Cut surface of brain shows slate grey cortex

c)       Multiple punciform haemorrhage is found

d)      Areas of infract may be found .

e)      Microscopically –

i)                    Dilation and congestion of cerebral capillaries .

ii)                   Perivascular haemorrhage .

iii)                 Presence of scattered areas of softening ad softening areas may be invaded by glial cells forming malarial granulomas .

5..  Gastrointestinal tract –

a)      The mucous membrane shows pigmentation of slate grey colour .

b)      Punctiform haemorrhages may be present .

c)       Microscopically –

i)                    Capillaries of mucous and submucous membrane will be congested

ii)                   There will be presence of parasitised R.B.C in the capillaries .

6.. Adrenal gland –

a)      There will be necrosis of zona fasiculata .

b)      There will be haemorrhage in zona reticulata .

c)       There will be presence of parasitised R.B.C and pigmented phagocytes in sinusoidal capillaries 

Main features of Malarial pathology

1. i)                    The cell of reticulo-endothelial system become densely pigmented with haemozoin pigment giving characteristic slate grey or black colour .
2. ii)                  There will be hyperplasia of reticuloendothelial cells
3. iii)                The lumen of the capillaries of the internal organs will be packed with infected R.B.C .
4. iv)                There will be congestion and dilatation of sinusoidal vessels . Perivascular haemorrhage may occur .
5. v)                  There will degenerative changes of parenchyma cells due to anoxia .
6. vi)                There will be fatty degeneration and ischemic fibrosis due to anaemia .
7.  

Life cycle of malaria parasite

The life cycle of malarial parasite in two different hosts like –

1 .  In man – Man represents the intermediate host of the malarial parasite . The parasite resides       inside the red cell and liver cell and reproduce by asexual ,method . Human cycle starts with the introduction of sporozoites by the bites of the infected female anophiline mosquito . Sporozoites are found in the salivary gland of the mosquito and it may vary from 950 to 2.00.000 or more . But a mosquito can inject 3000 sporozoites at each bite . The sporozoites are thread like curved organs measuring about 12µ in length and an elongated nucleus is present centrally . There is no pigment . The sporozoites will come into the blood after the bite of mosquito and wil enter the liver after 30 to 60 minutes .

Life cycle –

(a)    Pre erythrocytic schizogony – This phase will start in the liver . The cycle lasts for 8 days in plasmodium vivax , , 6 days in plasmodium falciparum and 9 days in plasmodium oval . In the liver sporozoites will form pre erythrocytic schizont and eacbh mature schizont contains about 12.000 merozites in case of P.vivax and 40.000 in case of P.falciparum . in case of p.vivax , P.ovale and P.malriae , some of the merozites enter the blood after completion of pre-erythrocytic schizogony and some re-enter the liver causing relapse . But in case of P.falciparum , all merozites will enter the blood . So , there is no relapse .

(b)   Erythrocytic schizogony – The parasite resides in red cells and this cycle last for 48Hrs in P.vivax , P.ovale ,  and P.falciparum and 72 Hrs in p.malariae . Trophzoite , Schizont and merozite – thses stages ill occur inside the red cell . .

                         The newly formed merozites will attack new R.B.C . In the R/.B.C some will develop into trophozoites and schizont stage and some will form gametocytes .

(c)     Gametogony – Some of the merozoites develop into gametocytes ( male or female ) instead of developing into trophozoites and schizonts . gametocytes will form in the R.B.C of capalaries of internal organ like spleen and bone marrow . Gametocytes of P.vivax appear in peripheral blood from the first day of fever . gametocyte will not cause any febrile condition . The maturation of gametocytes is completed in 96 Hrs .

(d)   Para-erythrocytic schizogony – This phase is absent in P.falciparum but persist in case of P.vivax , P.ovale, and P.malariae in the form of a local life cycle .

    2.  In Female Anopheline Mosquito – Mosquito represents the definitive host of the malarial parasite as there is sexual method of reproduction . The stages inside the mosquito are –

a)      A female anopheles will draw blood of an infected person and take both sexual and asexual form of parasite . But asexual form will die immediately in stomach of the mosquito .

b)      A mosquito may be infected after its blood –meal from an infected person when there is at least 12 gametocytes per cmm .in the infected person’s blood and also the number of female gmetocytres will be more than the number of gametocytes .

c)       Inside the stomach of the mosquito , the pigment of microgmetocytes will shw violentb movement and exflagellation occurs and it is charecterised by 4 to 8 thread like filamentous structures . They become detached and form microgametes . . On the other hand , there is no exflagellation of macrogametocytes . So , from one microgametocyte , one macrogamete will form .

d)      By the process of chemotaxis , microgmetes are attracted towards the macrogametes and unite together and form zygote . Zygote will form in 20 minutes to 2 Hrs afrter the mosquito’s blood meal from an infected person .

e)      Then the zygote which is an actively moving body , develops into ookinete or travelling vermicule .

f)       The okinete will penetrate epithelial cells of the stomach and lie below the outer limiting membrane of the stomach wall . Then it develops into a rounded mass surrounded by a cyst wall . This rounded body is called oocyst . The oocyst measures about 6 to 12 µin diameter  . This will contain a single vesicular nucleus and pigments granules of the macrogamete .

g)      The oocyst will mature and it will increase about 6 to 60 µ in diameter . By the successive nuclear division , there develops a large number of sickle shaped bodies called sporozoites .

h)      The sporozoites will come in the body cavity of mosquito . The sporozites will be distributed to various organs and tissues of mosquito through the circulating fluid . Then they will come to salivary glands and ducts , These sporozoites infect another person during blood meal of mosquito .

i)        Development of sexual cycle in the mosquito in different species –

1.        P. vivax – 8 to 10 days

2.       P.falciparum – 10 to 12 days

3.       P.malariae -  18 to 21 days

4.       P.ovale – 14 to 18 days .

Diagnosis of Malaria

1. i)                    Presence of malarial parasite can be diagnosed after examination of blood . The ideal time for collection of blood is at the stage when temperature has started falling after reaching the peak .
2. ii)                  Cultural examination is done only when there is a difficulty in differentiating the ring form of P.vivax and P.falciparum .
3. iii)                Serological test like specific complement fixation test and precipitin test by using special antigen of P.knowlesi .
4. iv)                Blood count .

Clinical features of malaria .

1.. Febrile Paroxysm -  Each paroxysm shows a succession of 3 stages and lasts for 6 to 10 Hrs .

a)      The cold stage -  The fever will start with rigor or cold stage . This stage lasts for 1 to 2 Hrs and it is followed by rise of teprature .

b)      The hot stage – This stage lasts for 1 to 4 hours with a feeling of warmth , headache ,and vomiting . The temperature may rise upto 105*F or more .

c)       (c)The sweating stage – This stage lasts for 2 to 3 Hrs . In this stage , the patient has rofuse sweating  and feels comfort .

Types of Fever

a)      Plasmodium vivax produces benign tertuian fever with a 48 Hrs cycle . Fever with quotidian periodicity , in double infection with plasmodium vivax is also noticed .

b)      Plasmodium falciparum produces malignant tertian malaria or pernicious malaria and also black water fever . Fever with tertian periodicity with a 48 Hrs cycle is noticed .

c)       Plasmodium malariae produces quartan fever with a 72 Hrs cycle . Fever with quotidian periodicity , onn triple infections with Plasmodium malariae is also noticed .

d)      Plasmodium ovale produces tertian malaria .

2.. Anaemia – Due to breakdown of R.B.C , anaemia of microcytic or macrocytic hypochromic type develop .

Causes of anaemia in malaria

1.        Rapid destruction of infected R.B.C by the sporulation of parasite .

2.       Haemolysis of non-infected R.B.C particularly in case of P.falciparum which will liberate haemolysin . Haemoglobinuria and black water fever may be produced .

3.       Phagocytosis and intracellular destruction of both infected and non-infected R.B.C by the macrophages of the spleen .

4.       Failure of organs to re-convert liberated iron into haemoglobin .

In case of P.falciparum , selective parasitisation of reticulocytes is noticed , so there will be loss of blood from numerous punctiform haemorrhag

Blood picture in Malaria infection

Erythrocyte count -  Count will be low , even upto 1million/cmm

Leucocyte count –

    Total count – The count rises during the rising period of temperature and this ranges from 10 to 20 thousand per cubic millimeter of blood . Leucopenia or normal count is restored after the paroxysm is over . The total count may be 3000 to 5000 / cmm .

    Differential count –

  

i)                    Neutrophils – 50 % to 70% ( neutropenia may occur ) .

ii)                  Lymphocytes , Eosinophils and Basophils – normal .

iii)                Monocytes – 10% to 20 % ( monocytosis ) .