lecture 1. introduction to parasitology, life cycles. Flashcards
What is a parasite?
A parasite is an organism (uni or multicellular) that lives in or on the living tissue of a host organism at the expense of that host. The biological interaction between the host and the parasite is called parasitism. Parasitism is a type of symbiosis, by one definition, although another definition of symbiosis excludes parasitism, since it requires that the host benefit from the interaction as well as the parasite. the parasite is dependent on the host for the completion of its life cycle. Another definition: a parasite is a type of predator that kills its prey slowly. A typical parasite will lay its eggs inside the host (prey), thereby ensuring a constant supply of food for the developing larva ( exceptions).
Enterobius vermicularis
LIFECYCLE
PINWORM
Life cycle: embryonate eggs ingested- (INFECTIVE STAGE)–> larvae hatch in the small intestine–> adults in lumen of caecum–> gravid female migrates to the puritan region at night to lay eggs–> eggs on perinatal folds-DIAGNOSTIC STAGE ( larvae mature in 4-6 hours).–> AGAIN
Enterobius vermicularis
FACTS
PINWORM.
- nematode
- very common in children, affecting billions of people worldwide.
- undergo 4 malts to mature.
- diagnosis: cello tape test and then observation under the microscope.
Parasitism
two-species association in which one species, the parasite, lives on or in a second species, the host, for a significant period of its life and obtains nourishment from it. This is a commonly accepted working definition of parasitism and using it we can emphasize several important features of the host-parasite relationship. The host is always the provider and the parasite is always the beneficiary. Many of these association produce pathological changes in the host that result in disease.
Types of parasites
Microparasites – protozoa
Macroparasites – Helminth are the flat parasitic worms: nematodes (roundworms, nemathelminths ), trematodes ( flukes), and a cestodes ( tapeworms)
Microparasites
Replicate in the host so infection levels can rise rapidly after a single infection event (theoretically from one infectious stage) e.g. malaria
Macroparasites
cannot generally replicate in the host – so the levels of infection are determined by the number of infection events and number of infective stages e.g. gut nematodes. Pinworms for example.
Life cycles
Diverse, but a number of basic patterns can be recognised.
1) Parasite never exposed and development and reproduction in a single host. Transmission by predation and scavenging. Simplest and rare. Trichinella spiralis
2) Parasite never exposed but development in two or more host species. definitive host ( sexual maturity) and intermediate host (larval, juvenile or non sexual). Vector : host that transmits the parasite directly to another host. Plasmodium, Wuchereria
3) Exposed but does not have active free living stages . the infective forms are protected by cysts ( protozoa ) and egg shells ( nematodes). Direct life cycles : 1 host ( Acaris-12 inches) or indirect cycle: intermediate and definitive hosts ( tapeworms-taenia-22 feet).
4) Active free living form is exposed to the external environment during development and transmission. direct or indirect life cycles and re entry into the host passive ( ingestion) active (penetration). examples: hookworks, schistosomes.
Life cycle 1
reproduction of parasite in host–> infective stage in same host-> host eaten, infective stage released during digestion–> development in new host. AGAIN.
Trichinella spiralis
Spiral Threadworm
Trichinella spiralis- life cycle
Life cycle 1. Threadworm.
-human infected by ingestion of undercooked meat (e.g. pork) - larvae in striated muscle–> larvae released in the intestine( 4 malts since they are nematodes)–> adults in small intestine –> production of free larvae ( rare)–> circulation ( blog and lymph)–> detection of started muscle ( just skeletal, not cardiac)–> genetic change in the muscle fibre and formation of a cyst–> either eaten and propagated or calcified. AGAIN.
Cysts are the diagnostic and the infective stage. transmission can occur between pigs and rodents or within these groups as well.
Trichinella spiralis - facts
- common parasite
- africa
- north pole expedition died of trichinella due to the ingestion of heavily infected polar bear.
- cook or freeze
Life cycle 2
reproduction of parasite in host (definitive)–> production of stages infective to vector–> uptake of stage by vector during feeding–> development of infective stages in vector–> transmission of infective stages to new host as vector feeds. AGAIN. For each host, there is only one stage that is infective. If you eat the parasite at a stage that does not grow in you, you will NOT get infected
Plasmodium- life cycle
see next lecture and edit then.
Life cycle 2. Female mosquito takes a blood meal and injects sporozoites –> blood stream–> liver–> into cells –> formation of a multinuclear schizont that divides to form about 20,000 merozoites ( over a week)–> each merozoite can infect a RBC and multiply to form 20-40 new merozoites ( cycle every 48-72 hours)–> trophozoites , unlike schizonts, grow in RBCs and gametocytes form and then they are take up by a mosquito , which is the definitive host. AGAIN gametocytes and trophozoite are diagnostic and sporozoites are infective.
Plasmodium- facts
-protozoa
expand this one a bit
Wuchereria bancrofti-facts
-nematode
Wuchereria bancrofti
a mosquito takes a blood meal and L3 larvae enter the skin–> adults in lymphatics–.:> adults produce sheathed microfilariae that migrate into lymph and blood channels. they block lymph flow and accumulate in the groin. –> taken up by mosquito–> shed sheaths and migrate to thoracic muscles–> Sexual cycle. AGAIN.
Infective L3 larvae; diagnostic microfilariae.
Life cycle 3
reproduction of parasite in the final host–> release os infective stages (eggs/ cysts ) to the outside world–> either transmission to final host (direct) by ingestion of infective stages or development in intermediate host ( indirect) that is later ingested. AGAIN
Ascaris- LIFE CYCLE
life cycle 3 direct. The parasite has to develop outside–> takes a while to embryonate but remain infective for years –> ingest–> larvae hatch out in the intestine–> bloodstream–> lung–> bursts out the blood vessels there–> crawls up the trachea–>back to the intestine–> male and female mate–> female lays eggs in the faeces ( 40-50 females/10,000 s eggs each) AGAIN
diagnostic: adults and eggs
infective : embryonated eggs.
Ascaris- facts
- worm- nematode
- 1 billion people infected
- infected throughout life
Taenia- facts
- cestode
- not as common as ascaris but quite prevalent as well
- examples: T saginata (cattle) T solium (pigs)–> intermediate hosts
Taenia - life cycle
number 3 indirect. oncospheres develop into cysticerci in muscle –> humans infected by ingesting raw or undercooked meat–> Scolex attaches to the small intestine –> eggs or gravid proglottids in faeces and passed into environment. –> cattle and pigs ( intermediate host) infected by ingesting vegetation contaminated with eggs or graves proglottids–> oncospheres hatch out in the intestine –> circulate into the musculature–> AGAIN
infective : oncospheres in muscle
diagnostic: eggs or gravid proglottids
Life cycle 4
reproduction of parasite in the final host–>release of eggs to outside world –> hatching of egg and development of infective stage–> either transmission to final host (DIRECT) or penetration into intermediate host and development of infective stage there (INDIRECT) –> transmission to final host ( ingestion, penetration of infective stages or intermediate host). AGAIN
Schistosomiasis- facts
- vector is fresh water snail
- trematode (s. mansoni, japonicum, haematobium)
Schistosomiasis- life cycle
number 4 indirect do a number 2 in water –> eggs hatch ireleasing miracidia–> these pnetrate snail tissue –> develop into sporocysts in snail–> snails shed free swimming cercariae into the water–> burrow through the skin–> lose tail during penetration to become Schistosomulae –> circulation–> portal blood in liver–> adult–> paired adult worms migrate to mesenteric venues of bowel, rectum - or venue plexus of bladder–> stool. AGAIN
infective: cercariae
diagnostic :s. mansoni, japonicum, haematobium eggs in faeces.
Necator
nematode. hookworm
Ancylostoma
nematode. hookworm
Necator and Ancylostoma
Life cycle 4 direct. Filariformlarva penetrates the skin–> adult in the small intestine–> eggs in faeces–> rhabditiform larva hatches in the outside world–> filariform larva. AGAIN.
Infective stage: filariform larva
Diagnostic : eggs in faeces
Dracunculus medinensis
Guinea worm
Dracunculus medinensis- facts
- hoped to be the second disease to be eradicated after small pox. 3.5 million cases worldwide in 1986 and just 22 in 2015.
- intermediate and definitive host.
- Jimmy Carter (NPP): education and getting people to filter water before drinking it.
- females up to a metre long, males pathetic.
- Water based infection.
- now seems that the number of dogs are harbouring dracunculus . We must eradicate it in dogs. Chad –> seasonal peaking in spring cause the dogs eat the annual fresh water fish harvests
Dracunculus medinensis- life cycle
Number 4 indirect¿?¿? L1 larvae consumed by a copepod (crustaceous) L3 after undergoing 2 molts in the copepod human consumes watwe without filtering and ingests copepods with L3 larvae. released when the copepod dies and they go to the stomach, where they mature and reproduce fertilised female egg goes to the skin ( after a year of infection), causes a blister and discharges larvae in water ( it is hot and itchy-the fiery serpent). AGAINDiagnostic : the female worm commences to emerge. Infective: copepods with L3.
