Medical Parasitology medical Part 1

Type of parasites

• Endoparasites: live inside it's host “infection”

• Ectoparasite: live outer surface of host “infestation”

• Obligate parasite : depends on host for nourishment, reproduction, habitat & survival

• Facultative parasite: capable of leading both free-living without host & parasitic existence

• Accidental/incidental parasite: establishes itself in host where it doesn't ordinarily live

• Erratic/aberrant parasite: wanders into organ in not usually found

Medically important parasites

Parasite

1. Protozoa

• Sarcomastigospora - flagellates, haemoflagellates & amoeba

• Coccidia - sporozoa

• Ciliophora - ciliates

2. Helminths

• Nematodes

• Cestodes

• Trematodes

3. Arthropods

• Ectoparasite

General characteristics of protozoa

• Unicellular, eukaryotic organisms

• Consists of cytoplasm & membrane-bound nucleus/nuclei

• High rates of reproduction:

1. Asexual (binary fission & schizogony)

2. Sexually

• Size ranges from 1-150 μm (require microscopy for detection)

Basic characteristics of flagellates & haemoflagellates

• Move by flagellum/flagella

• Reproduce by binary fission

• Haemoflagellates posses unique organelle-kinetoplast (contains DNA)

• Flagellates transmitted by ingestion of cysts

Basic characteristics of amoeba

• Consists of mass cytoplasm

• Move by pushing out ectoplasm to form pseudopodia (false feet)

• Binary fission

• Digested food stored as glycogen &/ chromatid bodies

• Form cysts (transmission through this stage)

Basic characteristics of sporozoa

• No obvious means of locomotion

• Complex life cycles

• Asexually bu schizogony

• Sexually by sporogony

• Intestinal coccidia transmitted cysts

• Malaria parasites (blood coccidia) transmitted as sporozoites by mosquitoes

Basic characteristics of ciliates

• Move by cilia (small hairs cover body)

• 2 nuclei - macronucleus & micronucleus

• Binary fission

• Form cysts (transmission through this stage)

Characteristics of nematodes

• Non-segmented cylindrical worms

• Mouth surrounded by lips. Some species (hookworm) mouth opens into buccal cavity

• Sexes separate (dioecious) : male smaller than female

• Female either viviparous (produce larvae)/oviparous (produce eggs)

• Live in tissues/intestinal tract

Characteristics of cestodes

• Tape-like body

• Made up of scolex(head) & proglottid(segments)

• Attaches to host by suckers (some species by hooks)

• Adult tapeworm live in intestinal tract

• Hermaphroditic, with male& female sex organs found in each mature proglottids

Trematodes of medical importance

1. Hermaphroditic flukes

• Male& female sex organs

• Flat, leaf-like worms

• Unsegmented

• Attch to host by suckers (oral& ventral)

2. Blood trematodes

• Male &female adults (not hermaphroditic)

• Adults found in blood

• 2 generations required to complete life cycle:

1. Asexual generation - multiplication occurs

2. Sexual generations - produce eggs

Terminology in Parasitology

• Host

• Vectors

• Life cycle & types of life cycle

• Development stages of parasites

Host

• Organisms that harbour parasite & provide nutrition & shelter

• 2 type of host

1. Definitive host

2. Intermediate host

Definitive host

• Organisms in which sexual reproduction of parasite take place(mosquito for malaria parasites/human for pig tapeworm Taenia solium)

• Organisms that mature/most highly developed form of parasite occurs ( human for Trypanosoma cruzi)

Intermediate host

Organisms that support immature/non-productive forms of parasites :

• Fish for tapeworm Diphyllobothrium latum

• Snail for fluke fasciola hepatica

• Rats/birds for protozoa Toxoplasma gondii

Other type of host

1. Paratenic host

• Organisms; parasites doesn't develop further stage but parasite remain alive & capable to infect another susceptible host

• Wild boar for lung tapeworm Paragonimus westermani

2. Reservoir host

• Organisms; parasite infect human can live & develop in absence of human host, commonly animals

• Potential sources of human infection (zoonosis)

• Dogs & rodents for Leishmania donovani

Vectors

• Latin; carrier

• Organisms; usually arthropods carries infective organism like parasite & virus from one host to another

• Types of vectors:

1. Biological vectors

• Parasites undergo multiplication, propagation & development inside arthropod's body

• Acquire pathogenic agents through blood meal

2. Mechanical vectors

• Transmit pathogens by their secretion/external surfaces of body

• Serve as mere contaminators

• Pathogens don't undergo multiplication/development inside their bodies

Life cycle & types of life cycle

• Whole process of parasite growing & developing

• 2 types:

1. Direct life-cycle

• Only one species host necessary to complete development of parasite(no intermediate host)

• Protozoa : Giardia lambia

• Helminth : Trichuris trichiura

• Only require human host through faeco-oral route

2. Indirect life cycle

• 2 or more species of host required for parasite to complete development (intermediate & definitive host)

• Taenia solium/malaria parasites:

1. Intermediate host - pig/human

2. Definitive host - human/mosquito

Development stages of parasites

• All parasite pass through series of development stage before the organisms reproduce & new cycle of development begins

• 2/several development stages : entamoeba histolytica(trophozoite& cyst)

• Cryptosporidium parvum :

1. Infective stage - oocyst in environment

2. In human - trophozoite, meront, merozoite, gamont & oocyst

• Malaria parasite; several development stages

• May exhibit different morphological characteristics for different species; trophozoite stage