This lecture is about the protozoa which infect the GIS. It is important before we start to mention the two types of diarrhea because diarrhea as you know is the most prominent symptom related to these infections. There are 2 types of Diarrhea. Invasive diarrhea : The most prominent problem the patient faces in this type is tenesmus which is when the patient has the urge to defecate but when trying to do that he can't and only small amount of stool passes with mucus and blood. In stool analysis : the most important thing is to find WBCs and blood ( either seen by eyes or occult " only by microscope, seen as RBCs " ). Examples of microorganisms causing it : Shigella. Spp : causing bacillary dysentery. Entamoeba.histolyca : causing amoebic dysentery. Non invasive diarrhea : No WBCs and blood are seen in the stool and it is characterized being of a huge amount. Examples of microorganisms causing it : Virbro.cholera : which causes severe watery diarrhea and is associated with high mortality and morbidity rates. ETEC : Enterotoxigenic E.coli. Giardia. Lamblia Cryptosporidium Microspora Cyclospora Note : You should memorize the type of diarrhea caused by each microorganisms we are going to study as you are going to be asked about this in the exam. P a g e 1
The Doctor part in this module will be about the parasites infecting the GIS. in general parasites are classified into Protozoa and Metazoa ( Helminthes or worms ). Helminthes are of three types : 1- round worms ( nematodes ) 2- Tape worms ( cystodes ) 3-flukes ( trematodes ). This lecture is only about the protozoa. The protozoa we are going to talk about are parts of the Sarcomastigophora which includes two groups : 1) the amoebas 2) the Flagellates. From the flagellates, we will talk only about the Giardia.lamblia. The doctor is supposed to talk about parts of the Apicomplexia which are : Crypotosporidium, Microspora, Isospora and cyclospora but he ran out of time, so you should read them by your own from the textbook ( Sherris Medical microbiology ). The doctor stressed on the role of salads ( mainly those in restaurants ) and non- chlorinated water in the transmission of some of these diseases.. The Dr. says : " Good physicians don t eat salads in restaurants ", because the components of the salads are raw ( not cooked ). Table 48-1 in the textbook shows the parasitic infections and their prevalence. I will write the points our dr. mentioned and put a simplified version of it for the most important figures. ( Table 48-1 ) / / Prevalence of parasitic infections Disease Estimated Notes Population Affected Amebiasis 10 % of the world are infected Estimated deaths : 40 110 thousands Giardiasis 200 million - Ascariasis 1.3 billion -A round worm Hookworm 1.3 billion - P a g e 2
For the other diseases in the table, you should just know the name of the disease and the organ it infects and some also the name of the microorganism. ( Most of these diseases are ones which we are going to discuss the next lecture ) Notes of the Dr. on Table 48-1 The Disease/s Notes Clonorchiasis and opisthorchiasis Parasites ( Flukes ) infecting the liver. Paragonimiasis Infects the lungs Fasciolopsiasis Caused by Fasciola. hepatica ( a fluke worm ) American and African trypanosmoes Blood Flagellates. Filariasis, onchocerchiasis and Infections of the skin Dracunculiasis. Trichuriasis - Strongyloidiasis - Enterobius Vermicularis -Doesn t infect the GIT Cestodiasis - The Amoebas The amoebas are a group of sarcomastigophora and the most important one of them is Entamoeba.histolytica. It is also called (Rhizopoda) as it is characterized by moving using pseudopodia. P a g e 3
Morphology The E.histolytica has two forms : The Trophzoite form : Which is the one that is multiplying and also the one that causes the disease. Morphology of the trophozoite of E. histolytica The nucleus : E. histolytica has a nucleus has a small central nucleolus called ( karyosome ) and chromatin material distributed on the periphery of the nuclear membrane giving what is called ( bulls eye appearance ). The cytoplasm : There is an endoplasm and an ectoplasm with a sharp demarcation between them ( notice the picture ). The endoplasm has pores and you can also see RBCs indicating the invasiveness of the infection. The cytoplasmc membrane : has lectins which induce cell mediated immunity and attach to gal-galnac receptors which is important for attachment and the activation od cell mediated immunity.* P a g e 4
In the book > Somewhat different from the Dr said. On the surface of the trophozoites, there are galactose specific lectins ( Gal / GalNAc ) capable of mediating attachment to the colonic mucosa and also capable of lysing the host cells upon attachment. This phenomenon is called parasite mediated or contact- dependent cytotoxicity. * The things in bold are different from what the Dr. said ** The doctor said that lectins are important for the activation of cell mediated immunity, a point that is not mentioned in the book. If you look to the picture of the trophozoite, you would see the pseudopodia which is important for locomotion. You can also notice that the trophozoites can be of any shape ( because of the presence of pseudopodia ) whereas the cyst form is round in shape. The cyst form : the dormant form which doesn t multiply and is found in the intestines or the environment. The morphology of the cyst form of Enamoeba. histolytica The cyst has 2 large chromatoid boidies or ( bars ) which are aggregates of ribosomes. These chromatoid bodies have blunted edges in Entameba.histolytica. Also, you can notice the nuclei whose number characteristically doesn t exceed 4. Each nucleus has a central nucleolus (karyosome) as in the trophpzoites. The Disease. Entamoeba.histolytica ( Histo : tissue, lytica : lysis ; means it causes lysis of the tissue. ). It causes invasive type of diarrhea ( called amoebic dysentery ) with ulcerative lesions in the lower part of the GIT " the colon ". The amoeba could be acute or chronic. The infection could be asymptomatic and that s depend on the milieu ( the environment ) the P a g e 5
parasites are found in. ( Also in the book, there are virulent and avirulent strains of the parasite ). An important feature of the amoebic dysentery disease that occurs in 5 % of the infected population is the extraintestinal dissemination of the parasites, mainly to the liver causing amoebic abscess. Pathology and pathogenesis : The parasites have lectins which have important functions ( see earlier ). Also, they secrete enzymes important for the invasiveness like cysteine proteases which are responsible for the ulcer formation. There are also enzymes called zymodemes which we can analyze in the lab for the identification of the invasive strains ( This point was not clear in the record, so I will ask the dr. about it ). These zymodemes include : Glucose phosphate isomerase, phosphoglucomutase and oxidoreductases. The ulcer lesions are characterized by having a flask shape, so they are called flask- shaped ulcers. The parasites only invade the mucosa until the muscularis mucosa and cannot invade more which gives the ulcer its shape, ( narrow in the periphery and wide in the middle ). In 5% of the patients, the parasites are transmitted by the portal circulation into the liver, mainly to the upper part of the right lobe, forming liver abscess. The dr wants you to remember this very clearly : " Every abscess seen in the liver is caused by Entamoeba.histolytica until proved otherwise. " The complications of this liver abscess is caused by the direct invasion of the parasites into the nearby tissues ; If the abscess is in the upper part of the right lobe and it extends to the lungs above, it will cause lung abcess. If it was in the left lobe ( and this is not the case most often ), the invasion into the heart may cause Cardiac tamponade which is a very serious complication. The Doctor also says that the parasites can go through the systemic circulation into any part of the body. Under the microscope, you would see trophozoited surrounded by amorphous granular eosinophilic material. Also, you would see neutrophils which are responsible for tissue destruction in addition to the enzymes and zymodemes secreted by the parasite. P a g e 6
The ulcers range in spectrum from non- specific lesions into flask ulcers which we talked about above. The adherence of the parasites by interactions between lectins and mucins is responsible for the lysis of the cells. And characteristically, the parasites are resistant to the MAC ( membrane attack complex C5b- C9) of the complement system. Clinical Capsule : From Sherris (( The doctor said it was important )) Amebiasis may be asymptomatic or produce intermittent diarrhea with abdominal pain. occasionally, sever dysentery can occur with abdominal cramping and a high fever. Invasion of the colonic mucosa is typical and may spread to the liver,where an abcess is produced. Clinical manifestations The clinical syndrome is dysentery ( Invasive diarrhea ). Remember : the invasive diarrhea : Blood, RBCs and most importantly WBCs are seen in the stool. The non-invasive diarrhea is severe and watery, remember the V.cholera and ETEC ( Entero- toxigenic E. coli ) Abdominal pain, tenderness, bloody stools. Fever only in third of the patients. All patients have heme positive stools, some as rectal bleeding without diarrhea. Fecal leukocytes might not be present ( It is not clear to me whether this point is related to the one before!!) Fulminant colitis might need colectomy. ( see the picture below ) Intestinal perforation, toxic megacolon, ameboma. The doctor only commented about ameboma. It is only a collection of granulation tissue that happens as a result of the healing process of the ulcerative lesion of the disease. P a g e 7
Its clinical importance is that sometimes doctors may think it is a tumor but when they take biopsy and see it under the microscope, they only find granulation tissue. The figure above shows a case of fulminent E.histolytica disease. In the cases of normal amoebic dysentery, the ulcerative lesions are characterized by alternating areas of normal and necrotic tissue not as seen here. P a g e 8
The Life Cycle The life cycle starts when a person ingests something ( fruits, vegetables or non chlorinated water ) contaminated with fecal materials. If this fecal material contains the cysts of Entamoeba.histolytica which is the infectious state, he will ingest these cysts. In fact, the infectious dose of these cysts is very low and sometimes one cyst can cause the disease. After the cysts are ingested and reach the distal ileum, they start to excyst forming trophozoites and the continue that in the cecum which is a very suitable environment for this process. then the trophozoites migrate through the ascending, transverse and descending colon and most colonization occurs in the sigmoid colon and the rectum. If the P a g e 9
person then defecates in the outdoors, he will contaminate the water or the vegetables and fruits and the cycle is closed. Some Factors Helping The Transmission Of The Disease : The poor hygiene habits, the crowding, The socioeconomic status, eating fruits and vegetables without washing them and drinking non chlorinated water all can help transmit the disease. The mode of transmission can also be related to male homosexuals and genital- oral sex. This mode is also exist in Giardlia.lamblia as we will see later. The importance of this point is also related to the HIV virus. It was noticed that the E. histolytica reduces the incubation period of the HIV virus ( which is normally 4-5 years ). This is because the lectins on the surface which stimulates the mitosis of the CD4 cells increasing the viral load. (( In the book, the E. histolytica produces a lectin like substance that is mitogenic to lympohcytes which can stimulate mitosis of HIV infected lymphocytes )). It is important to note that the disease is most common in children as they are always playing outdoors and more likely to ingest contaminated food. The nutritional state is very important, especially the protein rich diet for the immunity against the disease and the mal-nourished people are more likely to get the disease. As we said before, 10 % of the world are infected with this parasite. However, not all of them are symptomatic. (( from the book : Recently, they discovered that there is another amoeba identical in shape to E. histolytica called E. Disaper which is an avirulent one. This discovery will reduce the estimates of the prevalence of the E.histolytica from 500,000 into 50,000)). It is important to note that there are some people harboring virulent strains but are asymptomatic, which means that they can transmit the disease. So, it is important to screen people working in P a g e 11
kitchens of the restaurants and treat them in order to eradicate the carrier state. Host Immunity The patient will have an immunologic memory following a disease which make him less liable to the recurrence of the disease. High antibody titers can be noticed in patients having liver abscess which is important in the diagnosis of the parasite using serological techniques. The parasites are resistant to the complement system. The host also secretes surface IgA which has a protective role. Also, the cell mediated immunity plays a role. The lectin antigens found on the surface of the parasites can activate this CMI. The take of corticosteroids can make people more susceptible to disease as they suppress the immune system ( from the book : Corticosteroids are associated with the fulminant dorm of the disease as well as the pregnancy and the immunosuppression state ). If we are to design a vaccine, the best antigen to target is the lectins. Mucins have protective role. ( The more mucus you secrete, the more immune you are ). P a g e 11
Case Study Weight loss, Abdominal discomfort, and a Tender Liver. A 21-year- old college student (1) volunteered for a 2 year assignment as a missionary in a rural area of Central Mexico ( 2 ). Within 4 months of arrival, he developed mild diarrheal illness with a flatulence and abdominal discomfort that subsided spontaneously within a few weeks. six months later, he noted progressive weight loss over several weeks, a low grade fever, and right upper abdominal tenderness. He returned to the United States for medical consultation. The primary physical finding was an enlarges right lobe of the liver which was tender on palpation. An ultrasound study confirmed the presence of ulcer in that site. The diagnosis of an amoebic hepatitis abscess was seriously considered. The doctor Notes. 1) Why did they mention that he was a student? Because college student tend to eat in restaurants and not to cook food by their own, which increases the chances of eating contaminated food. The foods most commonly associated with these diseases are the ones that are raw ( not cooked ) ; like salads. Remember the Doctor saying " Good physicians don t eat salads in restaurants ". 2) Mexico as seen by people in USA is one of the developing countries that poor hygiene which increases the chances that the water there is contaminated and the restaurants food is also as well. the Dr says : " If E.coli was green, then Mexico would be a paradise " indicating how poor the hygiene is in Mexico. P a g e 12
The Diagnosis Amoebas in general are either pathogenic or nonpathogenic ( commensals ). Note that the commensals are not found normally in the gut and so their existence in the stool analysis means that the patient has ingested something contaminated with fecal materials which is associated with other bacterial or viral causes. For the diagnosis of E.histolytica, we first should know the type of the diarrhea. If it was found to be invasive, then we should put a differential diagnosis. And the most important differentials are : *bacillary dysentery ( by shigella.spp ) or * pseudomemranous enterocolitis ( A condition happening because of the abuse of antibiotics which permits C.difficile to cause this disease. The condition is characterized by dysentery- like symptoms so we should ask the patient if he was taking antibiotics. The diagnosis of amoebic dysentery depends on finding trophozoites or cysts in the stools. ( even if the patient is asymptomatic ) and the ones seen more in the stools are the cysts. If the stools are negative we can take direct mount smear from the endoscope, and the ones most likely seen here are the trophozoites. We can use imaging techniques to diagnose liver abscesses. And if an abscess is found, it should be aspirated under the guidance of x rays. P a g e 13
Serology can also play a role in the diagnosis by assaying for the Abs against lectins or Ags ( lectins ). The table above shows the differences between E.histolytica and other Entamoebas. You should know these differences in order to be able to differentiate between the disease-causing species and the commensals. The figure at the right shows a trophozoite under the microscope. You can notice the nucleus which has a central karyosome and peripheral P a g e 14
chromatin. You can also notice how big it is ( more than 12 Um ) and the presence of RBC indicating the invasiveness of this parasite. This figure also shows a trophozoite having the same features as the last figure. ( central karyosome, peripheral chromatin, ingested RBCs ). At the left side, you can see a cyst having 2 nuclei and a chromatoid bar with blunted edges. At the right, you can notice a nucleus having eccentric karyosome indicating that this is not Entamoeba. Histolytica but it is Entamoeba. coli. P a g e 15
In this figure, you can see that the cyst has 5 nuclei, and as we know by definition, Entamoeba. histolytica doesn t have more that 4 nuclei. so this is E. coli which can have up to 8 nuclei ( refer to the table ). P a g e 16
The figure shows the morphology of the nuclei of different amoebas. From the above amoebas other that E. histolytica, only Dientamoeba fragilis can cause diseases. The others are commensals. E.hartmanni is just like E. histolytica but is smaller than it. ( the dr said that it is also called E.dispar but in the book E.dispar has another story --- see the book or the second point in the treatment part below). The Entamoebas ( the upper row ) have chromatin material at the rim of the nuclear membrane whereas the lower row don t. Endolimax nana have pan shaped karyosomes. The karyosomes of Dientamoeba fragilis are segmenrted. Iodamoeba buetschlii have solar shaped karyosomes. Iodamoeba buetschlii has glycogen which stains dark when we apply iodine. P a g e 17
The size of the cyst of E. histolytica is 10 60 Um. The treatment An important point to remember here is to keep the hydration state of the patient. Even it is less encountered that the non invasive type of diarrhea, dehydration should always be considered. We should treat the asymptomatic carriers as they may transmit the disease to others. We should use Ag Ab studies to differentiate between E. histolytica and E. dispar. ( again the doctor mentions that E.dispar is the same as E.hartmanni but it is not the case as written in the book. E. hartmanni can be differentiated from E. histolytica by the size but E.dispar can be differentiated only by serology ) stool analysis follow up is important to follow treatment and we keep monitoring the patient until he becomes clear of the cysts and trophozoites. If a food handler is proved to have an asymptomatic state by stool analysis, he should not be allowed to return to work unless he is well treated. The drugs used are : Paromomycin Diloxanide furoate Tetracycline This is an antibacterial so why to use it in parasitic infection? Because the trophozoites eat bacteria enhancing their growth. So we give tetracycline ( a broad spectrum antibiotic ) to kill the bacteria not the parasites. Metronidazole ( Flagyl ) This is the drug of choice. It is associated with occurrence of teratoma in pregnant women ( the point is not clear! ). Tinidazole Dehydroemetine P a g e 18
We use it in cases of amoebic liver abscess. The ultimate treatment of a liver abscess is drainage of it either x ray guided or less commonly using open surgery. Prevention Proper habits after going to the toilet are very important, like washing hands,etc. Make sure that the restaurant is clean, and don t eat salads at restaurants. Chlorination of water is very important ( the municipal water is chlorinated and thus very safe). If unchlorinated water is needed, then it should be boiled. Proper waste disposal. The sexual practices like the oral fecal genital sex and the homosexuals may transmit the disease. The Flagellates We finished with the first group of the sarcomastigophora which is the amoebas. The second group is the flagellates. The table above shows the luminal Flagellates. The only one that can cause a disease in vagina is the Trichomonas.vaginalis. In the P a g e 19
intestines, the ones that cause disease are Giadria.lamblia ( also called Giardia.intestinalis or Giardia. doudenalis ) The flagellates are classified into intestinal, blood and tissue flagellates ( like leishmania and the trypanosomes ). There is also genital flagellates like Trichomonas. Vaginalis which. We get some of these flagellates from animals. Many of these flagellates. Trichomonas. tenax colonizes the mouth which is an important fact to know as it is a part of the dental plaque. Giardria Lamblia The disease caused by it is Non invasive diarrhea. So it is associated with dehydration. This disease is very common. Note : The trophozoite form of Giardia was first observed by Antonie van Leeuwenhoek in his own diarrhea stools. P a g e 21
Morphology. The trohozoite form. The disease forming stage. 12 Um in length and 9 Um in width Has 2 nuclei and a sucking disk in between them. There are 2 parabasal bodies. There are 4 pairs of flagellae. ( Anterior, Posterior, Lateral and Ventral ) Under the LM, it is seen as someone is looking at you, and it look like he has a beard which is the flagellae. The cyst form is the infectious stage. The Disease. Non invasive diarrhea Can be endemic ( found all the time ) or epidemic ( associated with outbreaks ) It is from Zoomastigophora class. Antigenic variation ( The doctor didn t finish this point as the lecture time had ended ) ---- From the book : Giardria trophozoites P a g e 21
are capable of changing surface proteins called ( Variant Surface Proteins ) so recurrence is possible. Lecture End You have to read pages 807 811 by you own. You have to continue the topic of Giardlia. lamblia also by your own. Sorry that the lecture is late but I am not the original one responsible for writing this lecture and I have been told to write it lately. P a g e 22