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PLASMODIAL INFECTIONS PLASMODIUM Phylum: Protozoa Sub-phylum: Apicomplexa (Sporozoa) Infective agent: Plasmodium falciparum, P. malariae, P. ovale, P. vivax  INTRODUCTION ◼ Is...

PLASMODIAL INFECTIONS PLASMODIUM Phylum: Protozoa Sub-phylum: Apicomplexa (Sporozoa) Infective agent: Plasmodium falciparum, P. malariae, P. ovale, P. vivax  INTRODUCTION ◼ Is the most important parasitic disease of man. ◼ It is a protozoan infection of RBC’s and is transmitted by the blood feeding female anopheline mosquitoes. ◼ Word Malaria comes from the Italians and literally means “bad air” (Mal aria) and they believed that it was caused by a bacteria Bacillus malariae. ◼ It was the French who implicated parasites in this infection. ◼ It is caused by Plasmodium sp.  INTRODUCTION ◼ Over 270m people are infected with about 1 –2m deaths each year mostly African children (90%) ◼ 4 species of Plasmodium infect man and these vary in their innate virulence depending on the type of RBC’s they infect. Plasmodium falciparum P. ovale P. malariae P. vivax ◼ Of these 4 common species P. vivax and P. falciparum accounts for 95% of infection. ◼ Malaria is found throughout the tropics and P. falciparum dominates in Africa.  TERMINOLOGIES ◼ Tertian malaria - fever occurs every 48 hours ◼ Quartan malaria - fever occurs every 72 hours ◼ Benign tertian- disease is seldom fatal ◼ Malignant tertian - disease is severe or usually fatal.  Plasmodium falciparum ◼Causes malignant tertian malaria with 36 – 48hr cycle ◼parasite density exceed 250,000 – 300,000 / µl of blood ◼Itcovers a large geographical range and is the most pathogenic of all four species. (Generally confined to the tropics) ◼Itcan plug capillaries and can cause severe symptoms/sequelae (cerebral malaria, lysis of RBC’s) ◼There is no true relapse (from residual liver stages i.e. hypnozoites) but there is recrudescence caused by parasites persisting in circulation at a sub-clinical level.  Recrudescence Recrudescence can be due to ◼a) incomplete or inadequate treatment as a result of drug resistance or improper choice of medication. ◼b) an antigenic variation. ◼c) infection by different strains.  Plasmodium vivax ◼ Causes benign tertian malaria with a 48hr cycle. ◼ It covers a large geographic range, more common in South America, N. Africa, India but rare in South Saharan Africa. ◼ It tends to have a “true relapse” from the residual liver stages. ◼ It infects young RBC’s. ◼ Parasite density rarely exceed 50,000 / µl of blood.  Plasmodium ovale ◼ Causes benign tertian malaria with a 48hr cycle. ◼ It covers a narrow geographic range (it is quite rare out side West Africa and South Pacific islands/ regions) ◼ It infects young RBC’s  Plasmodium malariae ◼ Is responsible for quartan malaria with a 72hr cycle. ◼ It covers a narrow geographic range; it is sporadic in distribution but relatively uncommon outside Africa. ◼ It infects older RBC’s. ◼ It is associated with recrudescence and “nephrotic syndrome” with no true relapse. ◼ P. vivax and P. malariae infect about 1 – 2% or less RBC’s, P. ovale infects less than 2% of RBC’s. ◼ P. falciparum infects or parasites up to 30 – 40%. ◼ Parasite density is about 10,000 / µl of blood.  INTRODUCTION ◼ Almost all deaths due to malaria and severe disease condition are caused by P. falciparum ◼ The other three parasites cause benign malarias and severe disease condition with these species is un- usual, however, occasionally patients with such infection may die from rapture of an enlarged spleen  EPIDEMIOLOGY A) THE VECTOR ◼ The main vector is the Female Anopheles mosquito ◼ Transmission does not occur at temperatures below 16 0C or above 33 0C because the development of the parasite in the mosquito (sporogony) cannot occur. ◼ These vectors show an important characteristic vector competence i.e. longevity. This is because sporogony requires a week or more to occur depending on the temperature.  EPIDEMIOLOGY ◼ Transmission is directly proportional to the Density of the vector Number of times of bites each day and also The survival of the vector after feeding ◼ Vectors differ in their natural density (abundance)/ feeding / resulting behaviors / breeding site preferences / flight ranges / choice of food (blood) / vulnerability to environmental conditions and insecticides. ◼ Anopheles gambiae is the most infective vector / are tough / long lived / naturally occur in high densities / bite humans frequently.  EPIDEMIOLOGY B) THE HUMAN HOST ◼ Human behaviour plays a major role in the transmission of malaria. There is the need for human reservoir of gametocytes to transmit the infection. ◼ In areas of high transmission, infants/young children are most susceptible than adults thus parasite densities tend to be higher in children and gametocytes tend to be detected more frequently in children. ◼ The younger age groups usually represent the main reservoir group and the main recipients of infection.  EPIDEMIOLOGY ◼ Children who survive infection achieve a state of premunition where infections cause little or no problems to host (children). ◼ Premunition is therefore a form of immunity that develops to control but not to prevent infection. ◼ It is also known that non-immune adults visiting areas of intense transmission tend to acquire premunition more rapidly than children. ◼ Falciparum malaria infections are more severe in pregnancy particularly in primigravidae.  CLINICAL EPIDEMIOLOGY ◼ Babies tend to develop severe malaria infrequently, if they do, mortality is high. ◼ Factors responsible for infrequent malaria in infants include passive transfer of maternal immunity and high haemoglobin F content of infants’ erythrocytes, which retard parasite development. ◼ Thus there may be lots of inoculation with sporozoites in the 1st year of life but blood stage infection may seldomly be severe. ◼ In the 1 – 3yr group, falciparum malaria can cause severe anaemia.  CLINICAL EPIDEMIOLOGY ◼ In less intense or unstable transmission, the age group severely affected extend to the older children leading to cerebral malaria ◼ In endemic areas - indigenous adults never develop severe malaria unless they migrate or emigrate because usually premunition prevents parasites from reaching dangerous levels. ◼ Premunition is generally low in areas where transmission is infrequent. ◼ Malaria transmission is usually seasonal, it is high in the rainy season; because coincides with the abundance of mosquitoes.  CLINICAL EPIDEMIOLOGY ◼ Deforestation, population migration and changes in agricultural practices have increased effect in transmission. ◼ Epidemics are caused by migrations / introduction of new vectors or changes in the habits of the vectors or human hosts. ◼ Thus malaria could be imported and this type of malaria is often mis-diagnosed. ◼ Transmission can also be by blood transfusion / transplantation or through the used of hypodermic needles which are contaminated by prior use by drug addicts.  LIFE CYCLE ◼ This is very complex and rich in morphological details. There are two main stages: a) Human Stages 1) Pre-erythrocytic schizogony 2) Erythrocytic schizogony 3) Erythrocytic gametogony b) Mosquito Stages 1) Fertilization, meiosis and ookinete formation 2) Formation of oocysts and sporogony ◼ Malaria provides an example of stage - development specificity of invasion. e.g. sporozoites – liver cells merozoites – RBC’s  LIFE CYCLE ◼ A) PRE-ERYTHROCYTIC (Hepatic Phase) ◼ Infection begins when the female anopheles mosquito inoculates plasmodial sporozoites into the blood stream of man ◼ These small motile sporozoites may be few in the inoculum (8 – 15) or can be about 100. ◼ After inoculation, sporozoites enter the circulation either directly or through the lymph channels and home to the liver parenchyma cells. ◼ This happens between (within) 45min all sporozoites would have entered the liver or have been cleared.  LIFE CYCLE ◼ The sporozoites live in the hepatocytes (liver cells) and begin asexual (schizogonic) reproduction. ◼ Schizogonic phase can last between 5 days (P. falciparum) to 15 days for (P. malariae) ◼ In P. vivax and P. ovale infections, a proportion of the intrahepatic parasites do not develop but go into a state of rest (quiescence) referred to as the hypnozoites (latent forms) which become active weeks / months later.  LIFE CYCLE ◼ These quiescent stages (sleeping stages) are responsible for relapses which characterize those P. vivax / P. ovale infections. ◼ During this asexual phase (schizogony), multiplication occur producing many thousands of merozoites which are released from ruptured infected hepatocytes. ◼ This phase is asymptomatic for the human host.  LIFE CYCLE ◼ B) ASEXUAL BLOOD STAGE DEVELOPMENT Erythrocytic schizogonic phase Erythrocytic gametogonic phase ◼ Released merozoites rapidly invade red cells. Attachment of parasite to RBC is facilitated by specific RBC surface receptors. e.g. In P. vivax - the duffy blood group antigen Fya or Fyb 29, 30. This antigen is absent in people from the West Africans region and this explains absence of P. vivax infection among these folks. ◼ Receptors to P. falciparum have been identified as glycophorins but receptors for P. malariae and P. ovale are not known.  LIFE CYCLE ◼ On entry the merozoites undergo several morphological changes and development from Ring Forms (trophozoites) → Schizonts → Merozoites ◼ In the early stages (less than 12hrs) the ring forms of all 4 species appear to be identical or similar under the microscope. ◼ They look like a signet ring or in P. falciparum like a pair of earphones with darkly stained chromatin in the nucleus, a circular rim of cytoplasm and a central vacuole – they are motile. ◼ As they grow – they consume the contents of the erythrocytes, usually the haemoglobin. Ring forms of P. falciparum in RBCs  LIFE CYCLE ◼ In about 24 – 26hrs of development, P. falciparum exhibits a high molecular weight strain variant antigen on the surface of infected RBCs (knob-like projections) which facilitate attachment to vascular endothelium. ◼ These RBCs disappear from circulation (sequestration) and parasites attach to the walls of the vessels a process called cytoadherence. ◼ The other 3 species (benign malaria) do not cyto- adhere and all stages of these parasites are found in the peripheral blood.  LIFE CYCLE ◼ P. vivax during growth enlarges the infected RBC leading to the appearance of red granules (pigments) throughout the RBC called Schüffners dots. These are also found in P. ovale. ◼ P. malariae produces characteristic band forms as parasites mature. ◼ Infected RBCs rupture releasing merozoites between 6 and 36 per RBC. ◼ Asexual life cycle is 48 hrs (tertian malaria) for P. falciparum, P. vivax, P. ovale and 72hrs (quartan malaria for P. malariae)  LIFE CYCLE C) POST ERYTHROCYCTIC STAGE SEXUAL STAGES AND DEVELOPMENT IN THE MOSQUITO ◼ After series of asexual cycles, a sub population of parasites develops (by gametogomy)into sexual forms (gametocytes), which are long lived and motile. ◼ The process of gametogony takes 4 days in P. vivax infections and more than 10 days in P. falciparum. ◼ Upon ingestion of male and female gametocytes in a blood meal the parasites become activated. They develop, multiply and fuse to form a zygote. Male and Female gametocytes of P. falciparum  LIFE CYCLE Within 24hrs the enlarging zygote (ookinete) becomes motile and penetrates the walls of the mosquito’s mid gut (stomach) where it encysts as an oocyst. The oocyst finally raptures to release myriads of sporozoites into the coelomic cavity of the mosquito. These sporozoites then migrate to the salivary glands to await inoculation into the next host Sporogony and takes between 8 – 35 days depending on ambient temperature / species of parasites / mosquito. Life cycle of the malaria parasite  HUMAN GENETICS AND MALARIA 1 Genetic polymorphism of several human genes affect – entry / multiplication /survival / development of malaria parasites and this determines the outcome of the infection. ◼ Parasite invasion of RBC’s depends on specific surface molecules on the RBC’s For P. vivax – duffy antigens For P. falciparum – glycophorin A ◼ Most black African are duffy antigen negative but not American blacks.  HUMAN GENETICS AND MALARIA 1 ◼ Malaria is seldomly found in carriers of the sickle cell trait (Hbs or AS) ◼ P. falciparum infected RBCs adhere to the walls of blood vessels via knobs that form as parasites mature in RBC’s (infected) ◼ This sequestration causes the infected or parasitised RBCs to hide in an area of reduced O2 tension which then facilitates sickling / potassium loss and killing of the parasite.  HUMAN GENETICS AND MALARIA ◼ Other genetic abnormalities that restrict the growth of malaria parasites within RBC’s are G6PD – deficiency and Thalassaemia (decrease or total absence of a normal globulin chain ) ◼ In this case there is a reduced ability for the RBC’s to produce NADPH via the pentose phosphate shunt, this results in an oxidative stress, which inhibits parasite growth. ◼ Also certain human leucocyte antigens (HLAS) common in West African also confer protection against severe malaria. Class 1 antigen HLA – BW53 and Class 2 antigen HLA – DRB1.1302  PATHOGENESIS AND CLINICAL MANIFESTATIONS The disease could be uncomplicated or complicated. ◼ The main manifestations of malaria are fever, chills and anaemia. ◼ The typical malarial paroxysm coincides with the simultaneous lysis of many RBC’s and the release of large numbers of merozoites. ◼ How these manifestations are maintained in vivo is not clear (synchronous parasite development) ◼ Only the intra-erythrocytic (asexual) parasites cause disease.  PATHOGENESIS AND CLINICAL MANIFESTATIONS There are 4 main processes. ◼ 1. Fever – the basis remain abscure ◼ 2. Anaemia a. Haemolysis b. Sequestration of infected RBC’s in the spleen. ◼ 3. Tissue Hypoxia – Resulting from anaemia and alteration in the microcirculation:- pulmonary oedema, renal failure, cerebral dysfunction. ◼ 4. Immunologic Events These include hypoglobulinaemia; antibody mediated splenic sequestration of platelets, immune complex disease,  PATHOGENESIS AND CLINICAL MANIFESTATIONS CLINICALLY ◼ The first symptoms are non-specific and resemble influenza and are similar for all 4 species. Non- specific signs and symptoms include: ◼ Fever (periodic, paroxysms) – headaches, muscular ache / vague abdominal discomfort / lethargy / lassitude and dysphoria / temperature rise / loss of appetite, chills, hepatomegaly and anaemia, joint pains, sweating.  PATHOGENESIS AND CLINICAL MANIFESTATIONS ◼ SPECIES – Specific syndromes ◼ P. vivax and P. ovale – fever and anaemia debilitate the patient but is unusual. ◼ P. malariae – mortality is rare, it is most often associated with immune complex disease including an irreversible glomerulonephritis in children in endemic areas. ◼ P. falciparum – can cause lethal complications especially in non immune persons and pregnant women.  PATHOGENESIS AND CLINICAL MANIFESTATIONS 5 ◼ Other complications associcted with severe P. falciparum infections include: ◼ Cerebral malaria ◼ Hypoglycemia (especially in pregnant women) ◼ Renal failure from acute tubular necrosis ◼ Massive intracellular haemolysis (black water fever) ◼ Pulmonary oedema  DIAGNOSIS ◼ Microscopic identification of parasites in blood is the most certain method ◼ Usually thin and thick blood films are prepared ◼ The thick film is examined to detect the presence of the parasites ◼ The thin film is examined to identify the species and to give estimate of the level of parasitaemia ◼ The films are stained in Giemsa’ stain or Leishman’s, or Field’s stains  ESTIMATION OF NUMBER OF PARASITES ◼ 1 – 10 per 100 high power field --- + (1+) ◼ 11 – 100 per “ “ “ --- ++ (2+) ◼ 1 – 10 in every high power field--- +++ (3+) ◼ more than 10 in every high power field-- ++++ (4+)  PREVENTION AND CONTROL ◼ Avoiding mosquito bites ◼ Use of drugs ◼ Prevention of mosquito breeding ◼ Elimination of all adult mosquitoes ◼ Health education  TREATMENT Available antimalarials are in 3 broad groups 1. Quinoline-related Compounds Quinines, quinidine, chloroquine, amodiaquine, mefloquine, Halofantrine, primaquine. 2. Antifols Prymethamine, proguanil, chlorproguanil, trimethoprim 3. Artemisinin Compounds Artemisinin, artemether, artesunate ◼ Of these three groups, the Artemisinin compounds have the broadest time window of action on asexual malaria parasites from medium sized rings to early shizonts. THANK YOU