Sources

Here is a list of the material used to write this blog

1. Roberts, L.S. 2005. Foundations of Parasitology pp 311-363
2. Schojorring, S. et al. 2007. "Incestuous Mate Preference By A Simultaneous Hermaphrodite With Stong Inbreeding Depression" Evolution. 423-429
3. Akira, I. et al. 2003. "Human taeniasis and cycticercosis in Asia". The Lancet. 362: 1918-1920
4. Eckert. J. et al. 2000."Echinococcosis: a emerging or re-emerging zoonsis?" Internations Journal for Parasitology" 30: 1283-1294
5. Lightowlers. M.W. 2000. "Vaccination against Cycticercosis and Hydatid Disease" Parasitology Today. 15(5): 191-195.

Article 3.

Incestuous Mate Preference By a Simultaneous Hermaphrodite With Strong Inbreeding Depression

Schjorring, S. 2007

• Inbreeding depression is considered one of the major selective forces for evolution of mating systems, generally favoring mating among unrelated individuals
• the cost of inbreeding avoidance must be weighed against the potenetial costs of inbreeding avoidance and the potential nongenetic and genetic benefits derived from breeding with related individuals
• when unrelated mating partner are scarce relative to related partners, the cost of inbreeding depression may be lower than the cost of forgoing mation
• the aritcles tests whether the tapeworm Schistocephalus solidus discriminates between related and unrelated mating partners and the fitness of the offspring
• two experiments were done to test this:

1. worms were given choices between related and unrelated parnters and their choices were documented
2. th e eggs and offspring produced from the various matings were exanimed

• the worms maing choices were: a sibling, a unrelated worm
• and selfing (self fertilization)
• it was found that despite the evidence for strong inbreeding depression mating preference was shown for close kin (the sibling)
• evidence for inbreeding depression: eggs produced by unrelated pairs hatched at a rate 3.5 times high then those produced by siblings, eggs produced by siblings hatched at a rate of 2.3 times higher then those resulting from selfing
• 3 possible resons for the benefit of breeding kin

1. indirect fitness benefits of in breeding: increase in indirect fitness is large enough to outweigh the decrease in direct fitness due to inbreeding depression
2. direct fitness benefits of inbreeding: direct benefits associated with incestuous breeding outweigh the cost of inbreeding
3. lower extinction risk of inbreeding populations: populations in which individuals regularly inbreed are less likely to go extinct that populations in which inbreeding is avoided

Article 2.

Vaccination against Cysticercosis and Hyatid Diseases

Lightowlers, M.W. 2000.

• a study of the tapeworms Taenia solium, Taenia ovis, and Taenia saginata
• all are capable of infecting humans
• T. solium infects pigs
• dogs are the definitive host of T. ovis and humans are for T. saginata.
• article examined the need for a vaccines
• vaccines against cysticercosis already in existance
• these vaccines are for the tapeworms T. sagunata in cattle and T. ovis in sheep
• it is possible these vaccines would be just as effective for vaccination pigs against infections of T. solium due to homologues protein coding
• vaccination against hydatid dissease is done in sheep
• vaccines were created using recombinant DNA technology
• genes encoding different antigens were cloned
• the results were used to produce the vaccines
• it was found that the combination of tow recombinant protein into a single vaccine gave a highly effective result
• the benefits of livestock vaccination to human morbidity and mortality are indirect
• a more direct approach would be to use protective vaccines against cysticercosis and hydatid disease in humans
• discussions have started to begin human trials
  

Cysticercosis and Crowding Effect

Cysticercosis

In some tapeworm speices, the oncosphere penetrates the gut of the intermediate host, and upon reaching the parenteral site (in any part of the body) metamorphoses into a cysticercoid or a cysticercus type of metacestode. A cysticercoid is a solid-bodied organism with a fully developed scolex.

Virtually any organ in the body can be infected with cysticerci. The most common location is the eye followed by the brain and then muscles, heart, liver, lungs and coelem. To the right it an x-ray of a infected thigh muscle.

In whatever tissue they invade, a fibrous capsule of host origin surrounds the metacestode (the exceptiong is when the cysticercoid develops in the eye). The effect of the cysticercoid depends on its location. Ocular cysticercosis can cause damage to the retina, iris or choroid. It also runs the risk of being mistaken for a malignant tumor, leading to the unnecessary surgical removal of the eye. Cysticerci in the brain can cause severe central nervous system malfunction, blindness, paralysis, disequilibrium, disorientation or epilepsy. Cysticerci in the skeletal muscle, skin or liver usually go unnoticed, except in the case of massive infection. Taenia solium is the most common tapeworm that forms cysticercoids in its intermediate hosts.

Crowsing Effect

An important condition which can affect tapeworm growth in the intestines is "crowding effect". Crowding effect proposes that within limits, the weight of the individual worms in the intestines of a individual is inversely proportional to the number of worms present. So the total worm biomass and the number of eggs produced are the same and are maximal for the host no matter the actually number of worms present.

It has been found that tapeworms in the presents of others with secrete "crowding factors" that influence the development of the other tapeworms in the population

Development

Tapeworm development can be generalized into four basic steps:

1. embryogenesis with the egg to result in a larva called the oncoshpere - the oncospheres of some species can be free-swimming in water
2. hatching of the oncosphere after or before being eaten by the next host, where it penetrates to a parenteral site
3. metamorphosis of the larve in the parenteral site into a juvenile called a metacestode - usually has a scolex
4. development of an adult from the metacestode in the intestine (called the enteral site) or either the same host or a new host

Article 1.

Echinococcosis: in emerging or re-emerging zoonosis

Eckert, J. et al. 2000

• a study of Echinococcus multilocularis the causative agent of human AE
• human AS is caused by the metacestode stage, it is a severe, progressive disease that can lead to death in as little as 10-15 years
• treatments are surgery and chemotherapy which can prolong the patients life, but a cure is only achieved if the metacestodes are completely eliminated
• has a wide distribution in central Europe
• sources of infection involve the red fox
• humans are infected with the parasite primarily through infected fox feces
• 3 reasons are given in the article for the apparent rise in the number of human infections

1. increasing fox populations and parasite prevalences - possibly due to reduced fox mortality after anti-rabies vaccination
2. invasion of villages and cities by foxes
3. the role of domestic dogs and cats in disease transmission to humans

- dogs and cats can be definitive hosts of the parasite by ingesting rodents harbouring the metacestode stages
- however there is little information on the actual role this might play in transmission to humans

- dogs are especially highly susceptible, whereas the susceptiblity of cats appears to be reduced

• also examined the factors associated with the spread of E. multilocularis, transmission dynamics, distribution, the incidence of human AE, awareness of the disease and whether it is ermerging or re-emerging
• Is E. multilocularis spreading? - unclear
• parasites may be spreading or it might just be a case of detection in regions it was always present in, but never discovered (could be due to greater awareness of the parasite)

PITT

Tapeworms are one of the many parasitic organisms capable of inducing the phenomenon called PITT (parasitic induced torphic transmission). This is a change in the behaviour, physiology or morphology of the host due to the infection by the parasite. The result is to facilitate transmission of the parastic to the next host, usually in order to complete its lifecycle.

The tapeworm is capable of manipulation the host for it's own purposes without the host's knowledge - definitely not a passive, dependent, helpless worm!

Examples of this phenomenon can be seen in copepods infected with Triaenophorus crassus. Infection with the tapeworm causes the copepod to swim near the surface of the water, where it is much more likely to be eaten by fish. This is benefical to the tapeworm as fish are its second intermediate host.

One of the most popular parasitics that cause PITT is Toxoplasma gondii:
http://en.wikipedia.org/wiki/Gondii