Introduction to Parasitology

• Parasitology studies the dependence of one organism on another, focusing on human parasites, their health effects, and impact on communities.
• Medical Parasitology is related to Tropical Medicine, which deals with diseases specific to tropical regions.

Types of Biological Relationships

• Symbiosis involves close associations between two species.
• Commensalism benefits one species without affecting the other, like Entamoeba coli in the intestines.
• Mutualism benefits both species, such as flagellates aiding termites in wood digestion.
• Parasitism benefits one organism (the parasite) at the expense of the host; Entamoeba histolytica causes amebic dysentery.

Parasite Classification

• Endoparasites reside inside the host (e.g., Plasmodium in red blood cells).
• Ectoparasites live on the host's surface, such as lice and fleas.
• Obligate parasites are completely host-dependent (e.g., tapeworms).
• Facultative parasites can live freely but may become parasitic if needed.
• Permanent parasites stay in or on the host for their entire life (e.g., Ascaris lumbricoides).
• Temporary parasites live on the host for a short period (e.g., bedbugs).

Types of Hosts

• Definitive hosts are where the parasite attains sexual maturity (e.g., humans for Taenia solium).
• Intermediate hosts harbor the larval or asexual stage (e.g., pigs for Taenia spp., snails for Schistosoma).
• Paratenic hosts transfer infection without parasite development (e.g., wild boars for Paragonimus).
• Reservoir hosts maintain the parasite's life cycle and can transmit infection to humans (e.g., pigs for Balantidium coli, cats for Toxoplasma gondii).

Parasite Transmission (Vectors)

• Biologic vectors facilitate parasite development inside the vector (e.g., Aedes mosquito for filariasis).
• Mechanical vectors passively carry the parasite (e.g., flies transporting enteric pathogens).

Sources of Infection

• Contaminated Soil & Water harbor Helminths like Ascaris, Trichuris, Hookworms, and Strongyloides.
• Contaminated Soil & Water harbor Protozoa.

Modes of Transmission

• Food transmits Entamoeba and Giardia.
• Undercooked/raw seafood or meat transmits Trematodes like liver and lung flukes.
• Taenia spp. are transmitted via Cestodes.
• Arthropods act as vectors, transmitting Mosquitoes (malaria, filariasis), and sandflies (leishmaniasis).
• Direct Contact & Autoinfection: Person-to-person contact spreads Enterobius vermicularis, lice and Self-infection spreads Strongyloides stercoralis, Hymenolepis nana.
• Ingestion: transmits foodborne and waterborne parasites (e.g., Entamoeba, Giardia, Taenia).
• Skin Penetration: transmits Hookworms, Schistosoma.
• Vector-Borne: Malaria (Anopheles mosquito), Trypanosomiasis (Tsetse fly).
• Congenital Transmission: Toxoplasma gondii crosses the placenta.
• Sexual Transmission: Trichomonas vaginalis.

Immune Responses to Parasitic Infections

• Innate Immunity includes physical barriers like skin and mucous membranes and chemical defenses like acidic stomach pH, lysozyme in saliva, and secretory IgA.
• Adaptive Immunity includes Antibody-Mediated (Humoral) responses like IgG, IgA, and IgE responses and Cell-Mediated (T-Cells) responses such as Th1 and Th2 responses against protozoa and helminths.

Epidemiologic Measures

• Incidence tracks new cases over time.
• Prevalence counts total cases at a given time.
• Intensity of Infection expresses worm burden measured in eggs per gram (EPG).

Treatment and Prevention

• Deworming Programs administer anti-parasitic drugs at a large scale. Preventive Chemotherapy offers mass treatment to reduce parasite transmission.
• Sanitation & Hygiene involves safe disposal of human waste and water purification.

Control Strategies

• Morbidity Control uses periodic deworming to prevent severe disease.
• Health Education (IEC) promotes hygiene to reduce infections.
• Environmental Management reduces breeding sites for vectors.

Eradication vs. Elimination

• Eradication defines permanent global reduction to zero cases (e.g., smallpox).
• Elimination means zero cases in a defined geographic area with continued interventions needed.

Protozoa General Characteristics

• Protozoa are unicellular and microscopic.
• They are eukaryotic, possessing a nucleus, cytoplasm, and membrane-bound organelles.
• Protozoa move using pseudopodia (Amoeba), flagella (Giardia, Trichomonas), cilia (Balantidium coli), or undulating membranes (Trypanosoma).
• Protozoa exist in two developmental stages: trophozoite (feeding and motile) and cyst (dormant and protective).
• Protozoa obtain nutrients by phagocytosis (Amoeba), pinocytosis, or cytostome feeding.
• Protozoa reproduce asexually via binary fission or sexually via syngamy and conjugation (Plasmodium, Ciliates).

Protozoa Transmissions

• Protozoa transmission occurs mainly via the fecal-oral route from contaminated water/food (Entamoeba histolytica, Giardia), vector-borne routes (Plasmodium, Trypanosoma), or direct contact-sexual transmission (Trichomonas vaginalis).

Medically Important Protozoa Classification

• Amoebae (Sarcodina) move with pseudopodia, including Entamoeba histolytica, Acanthamoeba spp., Naegleria fowleri, causing Amoebiasis, Amoebic Meningoencephalitis, and Keratitis.
• Flagellates use flagella, including Giardia duodenalis, Trichomonas vaginalis, Trypanosoma spp., causing Giardiasis, Trichomoniasis, Sleeping Sickness, and Chagas Diseases.
• Ciliates, like Balantidium coli, use cilia for movement and cause Balantidiasis.
• Apicomplexans (Sporozoa) have no locomotion (gliding), including Plasmodium spp., Toxoplasma gondii, Cryptosporidium spp. causing Malaria, Toxoplasmosis, and Cryptosporidiosis.

Medical Significance of Protozoa

• Protozoan infections pose significant public health concerns in tropical and subtropical regions because poor sanitation, lack of clean water, and vector-borne diseases facilitate transmission.
• Some infections, like malaria and amoebiasis cause high morbidity and mortality worldwide.

Prevention and Control of Protozoa

• Proper sanitation and hygiene (safe drinking water, handwashing)
• Vector control programs (mosquito nets, insecticides).
• Safe food preparation and storage are crucial.
• Mass drug administration (MDA) programs are implemented for endemic parasitic diseases.
• Vaccination and chemoprophylaxis are used for diseases like malaria.

Amoeba: Entamoeba histolytica

• Entamoeba histolytica causes Amoebiasis and is parasitic.
  • Mature cysts (10-20 µm) have 4 nuclei, while trophozoites (10-60 µm) have 1 nucleus and use finger-like pseudopodia for progressive.
  • Entamoeba histolytica infects humans (definitive hosts) and is passed as trophozoites or cysts in stool.
• Entamoeba histolytica causes intestinal amoebiasis: bloody diarrhea, abdominal pain, tenesmus, and weight loss.
  • It can also cause extraintestinal amoebiasis: an amoebic liver abscess (RUQ pain, fever, hepatomegaly), and a lung/brain abscess.

Entamoeba Coli

• Entamoeba coli is a non-pathogenic intestinal amoeba
• Entamoeba coli matures at 8 nuclei cysts (10-35 µm); irregular, unevenly shaped, and its motility is sluggish
• Entamoeba coli infects definitive hosts can survive in cold climates.
• Entamoeba coli is mistaken for E. histolytica

Entamoeba Hartmanni

• Entamoeba hartmanni is a small race
• Entamoeba hartmanni is usually 4-10 µm and contains 4 nuclei. At the trophozoite stage Entamoeba hartmanni is small, central and usually 3-12 µm.
• Entamoeba hartmanni does not cause previous confusion with e. histolytica due to its same size

Entamoeba Dispar

• Entamoeba Dispar is a non-invasive Entamoeba species.
• Entamoeba dispar is almost the same structure as Entamoeba Histolytica and measure 10-20 µm. This form has 4 mature nuclei with radial forms.
• Diagnosis of amoebas such as E. histolytica and E. dispar are morphologically identical. So testing such as PCR or ELISA testing is needed.

Identification and Challenges

• Entamoeba histolytica is the only pathogenic species in its group, causing amoebiasis. Entamoeba coli, Entamoeba hartmanni, and Entamoeba dispar are non-pathogenic.
• E. histolytica and E. dispar are morphologically identical, requiring PCR or ELISA for differentiation.
• E. histolytica actively ingests RBCs, while E. dispar does not (a key microscopic distinction).
• E. coli has up to 8 nuclei in cysts, differentiating it from other species.
• Mature cysts and trophozoites in loose stool are the infective and diagnostic stages.

Giardia Duodenalis

• Giardia duodenalis causes traveller's diarrhoea and is a pathogenic flagellate.
• Cysts can remain viable in water sources for months and the trophozoite has bilateral symmetry.
• Transmitted through the fecal oral route and through sexual routes
• Its duodenalis has 2 nuclei Metronidazole and tinidazole are used to treat this disease, and nitazoxanide also helps.
• The falling leave is caused by 4 pairs of flagella.

Trichomonas Vaginalis

• Causes trichmoniasis and transmits with STI or sexual infections.
• Most diagnostic tests involve saline and culture methods

Trichomonas Hominis

• Has five anterior stages
• Has survuves in moist intestianl environments
• Its commonly transmitted by oral or fecal routes

Free-Living Amoebae: Naegleria fowleri

• Naegleria fowleri, causes Primary Amebic Meningoencephalitis (PAM), a highly fatal disease.
• Naegleria can be passed through CSF, and is commonly transferred in geothermal waters.
• Naegleria fowleri have three stages: Trophozoite, Cyst and Flagellate. Trophozoite stages usually happen in CSF
• Treatment can be Amphotericin B, Miltefosine
• It has a rapid Onset and its is fatal

Free-Living Amoebae: Acanthamoeba spp.

• Acanthamoeba spp. cause Granulomatous Amebic Encephalitis (GAE) in immunocompromised patients, and they are free living
• Acantamoebas are transffered through 2 hosts, Trophozoite and Cyst It cause GAE if you are immunocompromised, and it causes AK
• The Amphotericin B can be used to treat patients with GAE.

General Parasite Information

• Naegleria fowleri enters through the nose, while Acanthamoeba is ubiquitous.
• Malaria life cycle stages injected come as Sporozoites injected into humans Falcigram is the best species and comes with unique banana features. P valley and p ovale can cause relapses sue to hypnozoites
• Schizognomy is the best form used.

Entamoeba Quick Facts

Malaria is the deadliest form of parasitic diseases, and spread rapidly Anopheles injects disease into bites, the most if not best of species P vivaz and P ovale leads to hypnozoites

General Nematode Information

• Nematodes usually known as roundworms, are usually cylinder and are nonsegmented. They also act in the digestive system
• Parasitic nematodes can cause morbidity and mortality in humans
• Transmit and penetrate through skin and ingestion
• These infections require general public infections in order to treat Controlling Nematode infections requires public interventions for public measures:
  • Improve sanitation -Practice Good Hygiene -Mass Education

Medical Parasitology: Classification of Parasitic Nematodes

• Internal Nematodes: Intenstinal
• Tissue Hematodes: Reside in the Tissues and bloods
• Blood transfers by worms to cause bacteria Ascaris is the cause of infection

Nematodes vs worms

• Nematodes have infective and diagnostic stages They are usually round and fertilize eggs They are transmitted mostly by sanitary eggs