What is Parasite? and their Types

What is Parasite? and their Types

What is Parasite?

All infectious agents are parasites that are dependent on any living Organism. For nourishment, growth and multiplication. The study of parasite that cause disease in man is called as medical parasitology. Clinical parasitology deals with those pathogenic Organism which are bigger in size than bacteria and fungi. Most of them have a sexual phase in their life cycle. The Organism from which the parasite takes it food is called the host. The most in which the sexual phase is seen is called the definitive host. The asexual phase take place in the intermediate host (secondary host). The intermediate host may act as a carrier for fress infection. The parasite that leaves on its host such as tick is called an Ectoparasite.

A parasite that leave lives in its host such as Ameba or Hookworm, is called an endoparasite. Permanent parasite leads a parasitic life throughout the complete period of its life. Facultative parasite live parasitic life when opportunity arise and obligatory Parasite cannot exist without a parasitic life. Parasites that cause harm to the host are pathogenic parasites, while those that benefit from the host without causing It any harm as known as commensals.

Transmission of Parasites in Human

Life cycle of a parasite is the phase comprised of differential, developmental stage through which it passes to grow, mature and reproduce. A mechanical vector (Example fly) is responsible to transfer a parasite from one host to another host. The parasite can be unicellular (Protozoa) or multicellular (helminth). Parasitic infections in man primarily involve of intestine, but can also include urogenital tract, liver, muscle and other organs.

There are following Main 3 routes of transmission by means of which parasite enters a human body.

1. Fecal oral route.
2. Penetration through skin.
3. By sexual contact.

Specimens used for the Diagnosis of Parasitic infections

The most common specimen used for the diagnosis of intestinal Parasitic infection is feces or stool sample. Following are other specimens which are also tested for the parasites.

1. Urine for blood fluke, infection.
2. Blood for blood parasite.
3. Urogenital swab for trichomonas.
4. Sputum for some roundworms that may pass through the lungs.

Medically important parasite can be divided into 2 classes.

1. Protozoa.
2. Helminths.

1.Protozoa

The Protozoa (Greek word “Proto” means first and “zoa” means animals) are considered to be a subKingdom of the Kingdom Protista. on the basis of Light and electron microscopic morphology, the protozoa are currently classified into 6 phyla. Most species causing human disease are member of the phyla. Sacromastigophora and Apicomplexa.

Protozoa are single cell animals found worldwide in most habitat. Most species of protozoa are free living, but all higher animals are infected with one or more species of protozoa. Infections range from asymptomatic to life threatening depending on the species and strain of the parasite and the resistance of the host. Some species of protozoa are considered commensals (normally not harmful), However, other are pathogens and usually produce disease. Protozoan disease range from verry Mild to life threatening. Individuals whose defenses are able to control but not eliminate a parasitic infection become carrier and constitute a source of infection for others. Many protozoan inflections can be life threatening in immunosuppressed patients, particularly patients with acquired immune deficiency syndrome (AIDS).

Most parasitic protozoa in human are less than 50 micrometre in size. The smallest forms are 1 to 10 micrometre long. However Balantidium coli may be about 150 micrometre long. Protozoa are unicellular eukaryotes. As in all eukaryotes, the nucleus is enclosed in the membrane.

Whai is Fungi?

Locomotion of the Protozoa

The organelles of protozoa have function similar to the organs of higher animal. The plasma membrane enclosing the cytoplasm also covers the projecting locomotory structure such as pseudopodia, cilia and flagella.

1. In the case of Entamoeba histolytica (superclass: rhizopoda) Mode of locomotion is by pseudopodia.
2. Organism such as trichomonas vaginalis and Trichomonas hominis. (Subphylum mastigophora), The locomotor organ is a flagellum.
3. Malaria parasite (class: sporozoa) do not have special organ of locomotion.
4. Balantidium coli (phylum: ciliophora) move by means of cilia.

Life Cycle of the Protozoa

During its life cycle, a protozoan generally passes through several stage that differ in structure and activity. The stage of parasitic protozoa that actively feed and multiply by frequently called trophozoites. Cysts are stages with a protective membrane or thickened wall some protozoa have life stage alternating between trophozoite and dormant cysts. protozoa in the cyst form can survive harsh conditions, such as exposure to extreme temperature or harmful chemical, or long period without access to nutrients, water, or oxygen. In cystic form parasitic species survive outside of a host and are able to transmit from one host to another host. The conversions of a trophozoite to cyst form is known as. Encystation, while the process of transforming back into a Trophozoite is known as excystation.

The Nutrition of the Protozoa

The nutrition of all Protozoa include organic materials, which may be particulate or in solution. Amebas engulf particulate food or droplets through a sort of temporary mouth. Pinocytosis is a method of ingesting nutrients material whereby fluid in drawm through small, temporary opening in the body wall, the ingested material become enclosed within a membrane to form a food vacuole. Digestion and absorption are performed in a food vacuole and the waste substance are ejected out. Protozoa have metabolic pathways similar to those of higher animals and require the some types of organic and inorganic compounds.

Reproduction of the Protozoa

Reproduction in the protozoa may be asexual (As in the amebas and flagellates that infect humans) or both asexual and sexual (As in the Apicomplexa of medical importance). The most common type of asexual multiplication is binary fission, in which the organelles are duplicated and the protozoan then divides into two complete organisms. Division in longitudinal in the flagellates and transverse in the ciliates. Some protozoa have complex life cycle requiring two different host species, other require only a single host to complete the life cycle. A single infective protozoan entering a susceptible host has the potential to produce large population. The rapid multiplication rate of many parasite increase the chances for mutation, Which leads to changes in virulence, drug susceptibility, and other cellular characteristics. Mutation related example are chloroquine resistance in Plasmodium falciparum and Arsenic resistant in Trypanosoma rhodesianse.

Some protozoans, such as Giardia Lamblia, (genius: Giardia), that inhibit the small intestine can significantly interfere with digestion and absorption and affect the nutritional status of the host. Similarly, extracellular or intracellular parasite that destroys cells while feeding can lead to organ dysfunction and serious or life threatening consequences.

Name of the Pathogenic Protozoa

1. Entamoeba histolytica
2. Giardia lamblia
3. Toxoplasma gondii
4. Balantidium coli
5. Cryptosporidium parvum

2. Helminths

Helminths are multicellular (Metazoa) worms or worm like animals. These are. Symmetrical animals and have 3 germs layers. They maybe parasitic or free living. Since they are multicellular, most helminths may be easily seen with the naked eye in the adult form. The clinically relevant groups of helminths are separated according to their general external shape and the host organ they inhabit. There are both hermaphroditic and bisexual species.

Classification of Helminths

The definitive classification is the based on the external and internal morphology of egg, Larval an adult stage. The helminths of importance to human can be subdivided into following 2 group.

1. Phylum Nemathelminthes (Class : Nematoda).
2. Phylum Platyhelminthes (Class: Cestoidea and trematoda)

Phylum Nemathelminthes (Class : Nematoda)

The nematodes are elongated and cylindrical appearance with both the ends often pointed. These are unsegmented worms without any appendage. The body of nematodes is covered with a tough cuticle. The size of nematode vary from the tiny trichinella worn which cause Trichinosis. To the long is Ascaris (about a foot long). Some nematodes are thread like as Filarial worm. and others such as hookworm are more rounded.

Name of Nematoda

1. Enterobius vermicularis (Pinworm)
2. Trichuris trichura (whipworm)
3. Ascaris lumbricoides
4. Hook worms
5. Strongyloides stercoralis
6. Trichinella spiralis

Platyhelminthes

Platyhelminthes (Greek word “Platy” Means “flat” and “helminth” means “worm” are a plylum of relatively simple bilaterian, unsegmented. Invertebrate animals with soft bodies. they do not have Body cavity and no specialised circulatory and respiratory organ. Their flattened shape allow oxygen and nutrients to pass through their bodies by diffusion. The lack of circulatory and respiratory organ limit. Platyhelminthes to size and shape that enable oxygen to reach and carbon dioxide to leave all parts of their bodies by simple diffusion. Hence many are microscopic and and the large species have flat ribbon like or leaf like shapes. The guts of large species have many branches, so that nutrients can diffuse to all parts of the body. Respiration through the whole surface of the body, makes Platyhelminthes vulnerable to fluid loss. they are not able to survive in dehydrated environments. Platyhelminthes survive well in freshwater and moist Terrestrial environments.

Cestodes

Cestodes can be subdivided as follows.

• Pseudophyllidean Cestodes: These posses false or slit like grooves and.
• Cyclophyllidean Cestodes: These posses cup like and round suckers.

Name of Cestodes

1. Taenia sagiinata (Beef tapeworm)
2. Taenia solium (Pork tapeworm)
3. Hymenolepis nana (Dwarf tapeworm)
4. Hymenolepis diminuta (Rat tapeworm)
5. Diphyllobothrium latum (Fish tapeworm)

The Trematodes (flukes)

Trematoda is a class within the phylum Platyhelminthes that contain 2 groups of Parasite Flatworms, commonly referred to as “Flukes”. The tomatoes or fluke are estimated to Include 18,000 to 24,000 species and are divided into 2 subclasses.

1. The aspidogastrea: which are obligate parasites of mollusks and may infect fish (including cartilaginous types) and turtles.
2. The digenea: which are obligate parasite of both mollusks and vertebrates and rarely infect cartilaginous fish.