Introduction : -The parasites are usually negligible and we don't take it seriously. - They cause diseases in the world. ( morbidity ) - Parasite means الطفيلي somebody who eats at someone else's table!!!! - Most parasitic diseases are chronic. - parasites may kill the patients ( causing mortality ) - The diseases of parasites are more common in the developing countries..... * parasites can last in the patient s body for long periods, that s why the most of these diseases of parasites are chronic. *The parasites are different from viruses and bacteria due to the complicated life cycle that they have. *you find that there are different morphologies not only one and also they can exist in different hosts they can exist in one animal or more, that depends on the life cycle that they have. *Unlike the bacteria which spread from one person to another rarely assuming different morphologies causes the disease and then it is transmitted to somebody else. *This is the feature that really differentiates the parasites from all other pathogens that can cause disease. Diseases: If you think about the spread of disease caused by parasites such as blindness, There are several infective causes of blindness : 1
-Bacteria : Chlamydia trachomatis ( the commonest infective cause of blindness). -Parasites : ( the 2 nd infective cause), Schistosomiasis (bilharzia) is another parasitic disease caused by parasite known as (Schistosoma). *when we talk about a patient in parasitology, we refer the patient as the host. *Host: is the animal or anything else that is harboring the parasite. Really when we think about diseases, they are important and that's why I am going to talk about these parasites and although it may be difficult because will have lots of names, life cycles and complicated details,but hopefully that you will eventually come up with something which is really understandable in your brain. Human beings who suffer of parasitic disease usually are referred to be "primary hosts". So if we have a primary host, we must have other types of hosts,and this refers to the complicated life cycle of the parasites. Note *GI tract, technically speaking, is outside the body because it is in connection with the outside through the oral opening and the anal opening but we consider it as inside so it is really endoparasites. *But we referred these as luminalتجويف (lumen means 2
*Transmission of parasites from one patient to another can be done directly i.e by contact ( like pediculosis ) *Parasites can be classified as two categories : 1- Ectoparasites : live outside the body ( on the skin, e.g : pediculosis ). *contact can spread the disease of this ectoparasites from one to another. 2-Endoparasites: live in the body. We have two types : 1)Tissue parasites (e.g :in the blood such as malaria), it can be also in the liver, subcutaneous tissue, ect. 2)Luminal parasites (in the GI tract such as worms). *The spread of parasites directly means that the parasite probably changes it's morphology and it is transmitted through a median to the other person. For example, Amoeba ( a genus of protozoa ) has a morphology known as trophozoite ( this is applied to all protozoa ), it s the form inside our bodies that divide, feeds and causes the disease,. - Sometimes it may have to be transmitted to other persons and usually you don't get the whole organism transmitted, it is actually transformed to something else called a "Cyst" *the cyst goes outside the body and then it is transmitted to somebody else. ( this is direct but not through the same organism or morphological state ) *the cause of this transformation that : 1)The cyst is more resistant than Trophozoite. 2)The Trophozoite can't survive outside the body. NOTE *bacteria has spores. *parasite has a cyst. 3
---------------------------------------------------- - Sometimes when the parasite comes outside the body,it undergoes a free living cycle : *in a patient comes out free living in the environment (gap stage) infect somebody else. OR in a patient cyst infect somebody else. ---------------------------------------------------- Sometimes the passage of the organism from one person to another through another host called "intermediate". For example, tapeworms move from one person to another through cows or pigs (the intermediate host). *The intermediate could be an insect as mosquito (Malaria transmitted through the intermediate mosquito). *The primary host is a human being usually. *The intermediate hosts can be insects (called vectors (ناقالت or animals. ----------------------------------------------------------- *Some parasites live in humans or animals and can move between them but they don t need to pass through the animal (as intermediate ). *The animal in this cycle is a source of infection but it is not an intermediate host so it s called "reservoir"..(مستودع للوباء الحيواني (reservoir means *In any disease (parasitic,bacterial ) when it exists in human and also in animals, it is referred to as zoonosis. - A zoonosis is an infectious disease that is transmitted 4
between species (sometimes by a vector) from animals to humans or from humans to animals. ( Wiki) *In some cases, primary host could be an animal and the intermediate could be a human. In other cases the human could be the both primary and intermediate. *In some parasites the life cycle can be more complicated with more than one intermediate host. Diagnosis: If you suspected symptoms, Parasite diagnosis can be achieved by several means: 1- Directly from the parasite itself. Ex: in cases of Ascaris, the patient might come to the doctor holding a worm that just came out of him!! [But this occurs rarely]. 2- By looking for forms of the parasite. Ex: in cases of protozoa look for cysts which are usually numerous in number and easy to find. In cases of worms worms produce eggs so look for the eggs. Parasite infection can be: - Silent, that is, symptoms might not be recognized (a person can have tapeworm infection for years without even knowing). - Associated with mild symptoms (like nematodas). - Or sometimes symptoms can be very serious that might lead to death! Samples can be taken from: a. feces; because many parasites are present in the GI tract, b. blood (ex: in cases of malaria), c. urine or any body fluid, d. tissue biopsy (in cases of tissue parasites) 5
3- Serological test; looking for specific antibodies in patient s serum, the antibodies produced against parasites are usually of IgE class, but you can also find IgM, IgE. Serology : looks for antibodies in the serum against certain antigens (parasites, bacteria, viruses,...) -Also an increase in the number of WBCs (eosinophils) in plasma is noticed due to parasitic infection Remember: Normally, eosinophils represent 2-3% of all WBCs, BUT in case of parasite diseases Any infective agent has antigens, these antigens can induce the production of specific antibodies which can detected and help in the diagnosis of the organism. Treatment: Of course there are many drugs to overcome the parasitic infection; some are safe but others are quite toxic. Classification: Parasites can be grouped into two major groups: 1) Metazoa: multicellular those are worms. 2) Protozoa: unicellular organisms, eukaryotes, their size vary; it can be small measuring about (3) microns or very large measuring about (70-80) microns in diameter. They can be intracellular or extracellular (majority are extracellular) depending on their size if it can fit in the cell. 6
RBCs have a diameter of (7) microns, Lymphocytes have a diameter of (10) microns, Macrophages have a diameter of (15-18) microns. Reproduction: Parasites increase in number by Binary Fission. This can be: A] Asexual (non-sexual) (no gametocytes involved), the organism simply divide into two, the two into four and so on. B] Sexual some of these parasites transform into male and female gametocytes, these will join to produce a zygote, which can divide giving rise to offspring. ** Usually the asexual binary fission occurs in one host, and the sexual in the other host. Ex: Malaria parasite divides asexually in humans (Primary Host), and sexually in mosquitoes (Intermediate Host). *Protozoa can multiply within the host, while Metazoa can t! That s why the disease caused by protozoa is more serious than that caused be Metazoa. Protozoa can easily cause fatal diseases due to their ability to multiply and produce large number. 7
Protozoa Classification: Protozoa are classified into different categories according to their morphology and based on their means of locomotion: 1) Flagellates: those who posses flagella which help in their movement. 2) Cillates: move using cilia. 3) Rhizopoda: move by pseudopodia Ex: Amoeba. Simple discussion of the Amoeba Life Cycle: Amoeba are present in the large intestine, let s say that you ate amoeba Trophozoite, you won t get infected because Trophozoite are very delicate and will die quickly so it transforms through a process producing at the end a cyst, which is smoother that Trophozoite and covered by a protective layer, thus can survive outside the body, this cyst Trophozoite: is the active form of the organism, that feeds, moves, metabolizes, and divides by binary fission, it s what causes the disease. If transmission of the disease occurs, Trophozoite can t survive outside the body. when you eat it, resists the stomach acidity and passes to the small intestine and due to hydrolytic enzymes in there, the outer layer will disintegrate releasing the nuclei, which will develop into Trophozoite and then move to the large intestine where it colonizes. *** Some parasites don t need to have an intermediate stage (cyst stage) in their life cycle. 8
Ex: Trichomonas viginalis: This parasite lives in the vagina in females and urethra in males, it can be transmitted directly to another person producing pathogenicity of the urethra, because transmission occurs directly and there is no need for the organism to go outside the body or pass through the stomach Trophozoite can simply be transmitted this is an example of a sexually transmitted disease. *** Malaria parasite can t be transmitted between humans directly and bypassing mosquito, except in the case of blood transfusion from an infected person. Prepared by : Malek abu-hazeem 9