Ascaridida

Ascaridoidea*

Heterakoidea*

Cosmocercoidea

Subuluroidea

Seuratoidea

Ascaridoidea

• Parasites in intestine of all classes ofvertebrates. Aquatic cycles use invertebrateand vertebrate (fish) intermediate hosts;terrestrial cycles use vertebrate intermediates;some such as Ascaris, Parascaris, Belascaris,are monoxenous .

• Monoxenousascaridoids aresecondarily derivedfrom heteroxenousforms

Nadler, S.A. and D. S. S.Hudspeth. 2000. Phylogenyof the Ascaridoidea(Nematoda: Ascaridida)based on three genes andmorphology: hypotheses ofstructural and sequenceevolution. J. Parasitol. 86:380–393.

Immunopathology in Ascaris

• As in most helminths, Ascaris infectionprovokes a polarized Th-2 response.

• JaK-Stat signalling of B-cells with IL-4 leadsto IgE production. IgE attaches to mast cellsin gut. On reexposure antigen can cross linkIgE on mast cells leading to degranulationwhich triggers inflammatory response.

Other Ascaridoids of importanceto humans.

• Anisakis spp., parasites in stomach andintestine of Pinnipeds, Cetaceans

• Pseudoterranova decipiens, parasites instomach/intestine of Pinnipeds.

• Both groups have life cycles involving hostfood chains: copepods-amphipods-fish-seal;euphausid shrimp-whale.

Ascaridoids cont’d

• Tococara canis, T. cati : common parasites ofhousehold pets. Infection may occur by:– Eating infected prey

– Eating infective eggs

– Transplacental

– Transmammary

Young Vs adult hosts

Spirurida

• Largest and most diverse order of parasiticnematodes. All use arthropodintermediates.

• 2 suborders:– Camallanina: use crustacean intermediates

– Spirurina: use crustaceans or insectintermediates.

Camallanus spp

• Parasites in intestine of fish and amphibia.

• Pathogen C. cotti, parasite of freshwater fishin SE Asia, disseminated throughout worldby tropical fish trade.

Dracunculoidea

• Parasites of fish, turtles, birds, mammals.Copepod intermediate

• Dracunculus medinensis occurs in man. Aserious pathogen that could be controlledthrough inexpensive community-basedapproach.

Spirurina

• 10 + superfamilies distributed in all classes ofvertebrates (mostly terrestrial).

• Most important human pathogens aremembers of the Filarioidea: e.g. Brugiapahangi, B. malayi, Wuchereria bancroftia,Onchocerca volvulus, Loa loa

Filarioidea

• Occur in extraintestinal sites in all classes ofterrestrial vertebrates (not in fish).

• Use haematophagus arthropods fortransmission.

• 2 families: Filariidae (2 subfamilies, 15 spp.)and Onchocercidae (8 subfamilies, 80 spp.)

Onchocerca spp.

• Adults occur in subcutaneous tissues ofgrazing mammals and man.

• Microfilaria occur in skin but often remotefrom location of adults.

• Transmission by blackflies (Simuliidae)

Blackfly vector needs highly oxygenated water(fast flowing streams).

Slave trade involve in introduction to theAmericas.

Pathogenesis

• Adults elicit little response, nor do intact skinmicrofiliaria which accumulate in face andconjunctiva of the eyes. But when microfiliaria diethey provoke a strong kerititis and thickening ofconjunctiva leading to blindness.

• Pathology associated with Wolbachia sp., anendosymbiont of Onchocerca, and acts throughstimulation of TLR4 receptor by LPS.

Brugia and Wuchereria

• Adults in lymphatics of Primates, Carnivores,Shrews, and Lagomorphs.

• Microfilaria (sheathed) occur in blood andtypically show marked circadian periodicityin numbers.

• Have Wolbachia symbionts that appear tomodulate the pathology of infection.

Pathogenesis

• Intact worms (adults or microfilariae) not aproblem but with chronic infection hostexposed to antigens released from deadworms including Wolbachia antigen.Resultant reaction to antigens leads toblocked lymphatics, scarring and othereffects.

Pathogenesis

• Treat with antihelminthic–leads to increasedlesions although it kills the worms!

• Treatment with Tetracycline leads to death ofWolbachia and its worms host.

• Current model uses Mongolia jirds (gerbils) whichshow little reduction in lesions even afterTetracycline treatment.

Loa loa