Monday, January 31, 2011

E. vermicularis: Nocturnal Nuisances

pinworm magnified

Intro- E. Vermicularis, also known as pinworm, is a thin, white nematode that lives in human intestines. Infection is seen worldwide in practically all economic groups, and is the most common worm infection in the US. The female emerges at night to lay eggs on the skin just outside the colon, which can cause itching. They can survive outside the body for 2-3 weeks, and can be transferred by touching a contaminated surface which can lead to transfer to the mouth and ingestion [1].

E. Vermicularis and Host Description- This parasite is a helminth (parasitic worm), of which humans are considered the only host. They predominantly affect children because thumb sucking is common among young children and eggs can easily be transferred to hands and then to the mouth. They are also common among institutionalized persons because they are easily spread when people are in close contact with each other [1]. E. vermicularis is a species of nematode, a group of helminthes that lacks a cardio-respiratory system, but has a digestive, nervous, excretory and reproductive system [3]. Males are 2-5 mm long and females are 8-13 mm long. This “pin” shaped tail is where the common name of pinworms comes from [4].

Image depicting clear picture of how the pinworms are found like cotton threads in the anus while the pin worms move to the perianal fold to deposit eggs.

Life Cycle- Humans can either ingest or inhale the parasite’s eggs because they are small and have a low enough density to become airborne [1]. Male and female E. vermicularis worms reproduce sexually, but their offspring only contain female larvae. The production of predominantly female larvae maximizes the reproductive fitness of the parasite because it maximizes the number of egg producing offspring. Male larvae are a product of parthenogenisis – the development of an unfertilized egg [2]. The larvae hatch in the small intestines and migrate to the large intestines where they mature and feed on blood and tissue of the host’s intestines. About a month after egg ingestion, females are sexually mature and can begin to produce eggs. Fertilization occurs in the large intestine and then at night the female migrates to the colon to deposit her eggs on the skin around the anus. After laying eggs, the female often dies, but occasionally returns to the large intestine. The male dies soon after fertilization of the female [4]. Once eggs are laid they become infective in six hours, but mortality is high because most larvae do not reach hosts. Eggs can survive outside the body for 2-3 weeks and can be spread by inhalation of airborne eggs, or hand-to-mouth ingestion after touching contaminated skin, clothing, or bedding [1]. The short, two month lifespan [4] and high fecundity both lead to high reproductive fitness of the parasite because these two life cycle characteristics both lend themselves to evolutionary efficiency and the ability to over-reproduce to ensure the continuation of the species.

Life cycle of Enterobius vermicularis

Ecology- An estimated 500 million cases of infection are reported globally, and it is the most common parasitic worm in the United States [5].The classical pathological effect of the parasite is perianal irritation and itching, but severe cases of infection can cause sleeplessness, weight loss, hyperactivity, abdominal pain, and vomiting. Peridiocally, after a female deposits her eggs near the anus, she migrates into a female host's vagina, instead of back into the anus. This produces irritative symptoms and can cause a vaginal discharge; infestation of the uterus can cause menstrual-like bleeding from the vagina [4]. Pyrantel pamoate and mebendazole are the primary drugs used to treat pinworms [5].

Example of parasite controlling time of redezvous- E. vermicularis nocturnally release eggs, which need 6 hours to become infective [1]. A person usually sleeps for more than 6 hours, giving pinworm eggs enough time to mature before host movement and potential spread of the parasite. If the eggs are ingested before they become infective they will not be able to grow into reproducing adults. So, it is evolutionarily advantageous for the parasite to lay eggs at night so that they have a sufficient amount of time to mature before being ingested.






Saturday, January 29, 2011

The Blinding Effects of Onchocerca volvulus


Introduction to Onchocerca volvulus:
Onchocerca volvulus is a parasitic nematode that infects humans via epidermal penetration from female black flies (Simulium), and causes the disease known as Onchocerciasis, or "River Blindness." [1] The majority of infections from O.volvulus occur in regions of West Africa; however, some cases have been discovered in sub-Sahara Africa, Mexico, Venzuela, Guatemala, and Ecuador. Although infection from O. volvulus is not fatal, reactions to this parasite can be quite unpleasant and painful.[3] These reactions include destruction of the elastic tissue and formation of redundant folds in the skin, loss of pigmentation, and in the most extreme cases, the skin of the host resembles the skin of a very old normal subject. [2] O.volvulus also causes long-term corneal inflammation, or Keratitis, and thickening of the corneal stroma, which leads to permanent blindness. [1] Onchocerciasis cannot be prevented or cured; however, available medicine can offer short-term pain relief.[4]
Description of Onchocerca volvulus:
O. volvulus is part of the family Onchocercidae in the order of Spirurida, which targets humans through transfer from its vector host, the female black fly. In its vector host, O. volvulus is usually found in the saliva within the proboscis so that when the female fly lands on a human for its "blood meal," O. volvulus can be transferred into the blood of the host. Once the parasite enters the blood of the primary host, it migrates to the subcutaneous tissue where it forms painful nodules that are visible through the skin. [1] O. volvulus can also enter the eyes of the host through the ciliary vessels and nerves under the bulbar conjunctiva into the cornea and the optic nerve; however, the major reactions of O.volvulus do not occur until after the death of the parasite. Once the parasite dies it causes an inflammatory immune response within the host and formation of secondary cataracts and ocular lesions, leading to progressive blindness. It also causes inflammation of regional lymph nodes, causing the nodes to protrude and enfold into pockets of skin. Extreme cases of this can be classified as minor elephantiasis. O. volvulus microfilariae, the beginning larval stage, measure 300 mm in length and 0.8mm in diameter, and contain sharply pointed, curved tails. [2]

Life Cycle of Onchocerca volvulus:

The life cycle of O. volvulus begins when a female black fly takes a blood meal. O. volvulus microfilariae, found in the dermis of the human host, is ingested by the female fly. The microfilariae then penetrates the gut of the fly and migrates to the thoracic flight muscles where it enters the J1 larval stage. Once the microfilariae matures into the J2 larval stage, it migrates to the proboscis of the fly and resides in the saliva. Here the O. volvulus matures into the J35 larval stage and passes from the saliva of the fly to the blood of a human through the fly's pentration of the human's epidermis. The larvae then migrates to the subcutaneous tissue, forming a nodule that matures into an adult worm over a period of six to twelve months. The small adult male then migrates to the subcutaneous tissue to mate with a large adult female. The adult female usually produces 1,000 to 3,000 microfilariae per day. The eggs mature to the first stage of the microfilariae and are released into the subcutaneous tissue. The microfilariae are then taken up by a female black fly during its "blood meal," mature over a one to three week period, and the O.volvulus life cycle begins again. The life span of the microfilariae is usually one to two years and the life span of the adult worm can be up to fifteen years. [1]

Ecology of Onchocerca volvulus:

O. volvulus cannot survive in the outside environment; therefore it constantly remains within a host, whether it be the black fly or a human. This parasite causes no harm to the intermediate host and only causes harm to its primary host after the parasite's death. Upon dying the parasite causes inflammation in various areas of the human body, producing nodules that protrude from the skin. This inflammatory response also causes damage to the optical nerves, causing blindness, which is the origin of the disease's name. As previously stated, there is no preventative vaccine or cure for the disease caused by this parasite, but medicine can be taken to temporarily alleviate the pain. [2]

An example of Onchcerca volvulus tranmission and relation to slavery:

O. volvulus is transmitted from human to human through the bites of black flies. Although the majority of the infections still occur in Western and Central Africa, the parasite and the debilitating disease it causes has migrated to other countries, such as those located in South and Central America. This migration is thought to be the result of the slave trade from Africa to these countries in South and Central America. [3] Other diseases that came over with slavery killed many slaves before landing in the New World, reducing the spread and effects of those diseases;however, the disease caused by the aforementioned parasite is not fatal so it was successfully transferred to inhabitants of the New World, causing this debilitating disease to spread to those who forced the Africans into slavery. So, while this parasite is certainly not the cause of the slave trade from Africa, it could be seen as a form of unintentional retaliation from those forced into slavery, and an example of how a small parasite can somewhat alter society and history.






Friday, January 28, 2011

Invasion of the Tongue Snatcher, Cymothoa exigua


Introduction to Cymothoa exigua:
The world of parasites can only be described as interesting. One parasite that enhances this claim is the Cymothoa exigua. This parasite seems to have a parasitic relationship with its hosts the Spotted Rose Snapper, Lutjanus guttatus, and the Red Snapper, Lutjanus peru. The Spotted Rose Snapper is found in all Mexican coastal fishing waters on the Pacific coast south to Guatemala, with the exception of the Pacific Side of the Baja California Sur peninsula and the oceanic islands [2].

Cymothoa exigua:
Cymothoa exigua is part of the family Cymothoidae in the order Isopoda which are known to target fish as their host. It usually found in the gills or the mouth of the snappers. If it the parasite is a male, it stays in the gills. If it is female it enters the fish through the gills and makes its way into the mouth and attaches to the tongue. Once attached to the tongue, it feeds on the blood until the tongue atrophies. This is when it gets interesting. Once the tongue is gone the parasite attaches to the stub of the tongue and then acts as the tongue and steals some food that the fish eats. The males can grow to a length of 8 to 19 mm while the females can grow to 21 to 37 mm [3].

Lutjanus guttatus and Lutjanus peru:
These fish belong to the Lutjanidae family, otherwise known as the Snappers, in the order Perciformes. These fish usually grow 15-18 inches long but have been found at two and a half feet and is found around 250 feet below the surface over sandy bottoms and not around rocky reefs [2].

Life Cycle of Cymothoa exigua:
Not much is known about the life cycle of this parasite. What is known is the parasite enters through the gills of the snapper. The parasite also sexually reproduces. If there is no female inside the fish and there are 2 males, one of the males can turn into a female after it grows to 10 mm [3]. How the parasite’s eggs are released is not known. Data analyses and reviewed literature allow proposing the hypothesis that the snapper is infested early in its life cycle by severa1 isopods at once with successful implantation of some of these. The life cycle of the isopods could be completed in the host and after a female of C. exigua finishes her cycle and dies, it may be replaced by a male breaking this sequence when no other male is available [3].

The parasite does not cause much harm to the host. The females only replace the tongue. The only damage that is caused is by male C. exigua. “Additional reports about the damage caused by male parasites include hematophagy (Morton, 1974; Brusca, 1981) and excessive mucus secretion on gill chamber surfaces which eventually affect the respiratory process” [3]. It has not been shown to affect the growth of the fish however so the harm caused to the host is minimal.

An example of the diversity of parasites. Sure many parasites feed on the blood of their host, but how many feed on the blood of a host until the organ atrophies and then functions as the organ itself? Only one. This is the only known parasite to replace an organ that it atrophies.

And now a video for your enjoyment! Don't worry though this parasite does not attack humans and the reason this fish was found in New Jersey and other places is because it was imported in.

The Colbert ReportMon - Thurs 11:30pm / 10:30c
Craziest F#?king Thing I've Ever Heard - Tongue-Eating Parasite
Colbert Report Full EpisodesPolitical Humor & Satire Blog</a>Video Archive



Thursday, January 27, 2011

Diphyllobothrium latum, A Very Macroscopic Parasite

Introduction to Diphyllobothrium latum:

Diphyllobothrium latum is a tapeworm that is spread to humans via raw or undercooked fish. This tapeworm is the largest that parasitizes humans. It can also parasitize other mammals. It can be spread through salmon, trout, perch, walleyed pike and other fish commonly consumed by humans. These fish become infected by eating a smaller infected fish who becomes infected by ingesting an infected crustacean, t
he first host in the life cycle of D. latum. The majority of infections occur in the Northern Hemisphere, Europe, North America, and Asia being major targets for this parasite. But the parasite is also found in other locations. The parasite does not cause any fatal diseases and infection by D. latum is not fatal. It can, however, cause diarrhea, vomiting, weight loss, discomfort, and a deficiency of vitamin B12. And because D. latum become so large, it may become an obstruction in the intestines, leading to complications. [1]


Description of Diphyllobothrium latum:

D. latum is an organism that grows throughout its life, reaching lengths of up to 30 feet. They are slightly yellow to white in color and have flat bodies. Lacking a mouth, nutrition is obtained by osmotrophy. D. latum are hermaphrodites and are constantly producing eggs inside the host. Upon entering a host, the parasite travels to the intestines where it matures and reproduces. Eggs leave the host via the host's fecal matter. D. latum has basic sensory organs located at the scolex (anterior end of the parasite where attachment to the host occurs) that can detect tactile (touch) stimuli. [4]

Life Cycle of Diphyllobothrium latum:

Eggs of D. latum develop into an embryo in fresh water. There, they are ingested by a crustacean and develop into larva. Small freshwater fish prey on the infected crustacean and the parasite moves to a further stage in its development. These small fish are then eaten by larger freshwater fish, fish that are a food source for mammals, including humans. The parasite will die if it is cooked properly, but if ingested raw or undercooked, the parasite will infect its final host, a mammal (often humans.) Upon ingestion, the immature tapeworm will mature into an adult and migrate to the small intestines to grow and reproduce. It is here that the parasite will live out the rest of its adult life, producing up to 1,000,000 eggs a day. [2]

Ecology of Diphyllobothrium latum:

D. latum inhabits freshwater lakes and streams. At each stage in its development, the parasite has a different habitat. From water they inhabit crustaceans, then fish, then a mammal. [4] This parasite does not pose a great medical risk to humans, though it may cause symptoms such as the ones mentioned above. It may also cause anemia due to vitamin B12 deficiency. There are medicines that can treat the parasite and the symptoms. There are also preventative methods such as proper preparation of fish. [1]

Diphyllobothrium latum, An Example of a "Stage 3" Parasite:

In The Art of Being a Parasite, Claude Combs proposes that there are three stages of parasitism. First stage parasitism means a parasite is not entirely inside its host and is not completely dependent on it for survival/reproduction. Second stage parasitism is where the parasite is to some degree in its host yet maintains a lot of contact with the environment. [5] And stage three parasitism can be exemplified by D. latum. At this stage, the parasite no longer has direct contact with the environment (outside of the host) and relies on the host for the expulsion of its eggs and for nutrition. An advantage that wasn't mentioned in class about being a stage three parasite (related to protection) is "hiddenness." The guinea worm we mentioned in class creates sores on the lower extremities of its host and breaches the skin when it senses water (making it a stage 2 parasite). In a human host, this communication with the environment prevents a threat to the success of the parasite because the human is now aware of the parasite. For a stage three parasite like D. latum, its entire adult life is carried out inside the host. On top of that, being infected with the worm is primarily asymptomatic. This acts as a "camouflage" for the parasite (in a human host with access to medical treatment.) It seems to me that it is an evolutionary advantage for a parasite to be a stage three parasite and remain hidden from its host. The longer it remains unknown to the host or the host's immune system, etc., the more eggs and therefore the more of its own genetic material it is able to pass to a new generation.


[5] The Art of Being a Parasite, Claude Combs

Wednesday, January 26, 2011

Sarcoptes scabiei, a Manifest of a Parasitic Relationship

Relative Species:
- Homo sapiens
- Sarcoptes scabiei
Sarcoptes scabiei utilizes the upperdermis of humans to produce eggs and to travel from host to host. Parasite species is located globally with no specific interest in race, socioeconomic class, and climate. Reported cases are estimated at at least 300 million annualy [1]. Symptoms of infection involve an extreme itchy feeling that produces rashes and sores.

Sarcoptes scabiei and Host Description:
- This parasite is responsible for an infection known as scabies. This tiny mite’s name is derived from scabere, the Latin word meaning to scratch [2]. Sarcoptes scabiei is an ectoparasite in which humans serve as the only host [3].

Life Cycle:
- Sarcoptes scabiei possess a relative simple life cycle compared to most parasites[1]. These mites wander on the surface of your skin to find a suitable place to burrow into. Once the females are in place they release eggs, generally 2-3 which hatch in approximately 4 days. Upon hatching, a larva emerges which will become a nymph after several moltings. Continuous moltings lead to the adult form [2].

- This parasite causes an infection, but not necessarily a disease. Recall that an infection is basically the body’s initial reaction to the pathogen. In this case, inflammation of the epidermis as a result of prolonged scratching is the main symptom of Sarcoptes scabiei.

An Example of True Parasitism:
- Up through current lectures in parasitology, we are slowly approaching a clearer definition of a parasite. A parasite usually benefits from it's host, while the host is left at a disadvantage. The parasite, upon successfully establishing a foothold in the host, has not only shelter and nutrients, but most importantly a place to reproduce and to pass beneficial genes to the next generation. The debilitated host, in the case of harmful parasites, now has to cope with the infection. If an individual with a case of scabies is infected, the parasite obtains a place to disperse offspring as well as the potential to travel via human skin to skin contact.
Future Questions and Observations:
-Upon describing this parasite, one might wonder why this parasite is harmful if it doesn't for the most part actually penetrate and live inside the body. What must be taken into consideration is the location that the parasite utilizes. Eventhough only our upperdermis is affected, humans depend on the the integumentary system especially the skin as our first line of defense against pathogens. When the skin is utilized by this species, the skin is left in a reduced state thus making the host more suspectable to other foreign invaders. Superficially, no pun intended, their is no harm done, but what happens to the female mite upon death? Does it simply just blow away and the skin fills in the hole like modern Departments of Transportation fill in holes on the highway, or does the carcus become a nest to other microorganisms?

-Perhaps another question that can be addressed is why humans are the only organism in which this host can infect.

Wednesday, January 19, 2011

Welcome to our Themes of Parasitology Blog!

We are a group of students studying parasitology at Mercer University in Macon, GA. This blog is a way for us to share our knowledge of parasites with the rest of the world. Our goal is to publish posts that give a general description of parasitic and mutalistic relationships as well as elaborate on some of the general strategies used by symbionts and their hosts.

We are reading Carl Zimmer’s “Parasite Rex” [1] and Claude Combs’ “The Art of Being a Parasite” [2] as part of our class. You may find that our posts complement their texts.

The general format of each post is as follows:

The species involved (specifically if reasonable) and the main biology of the relationship. General information such as global distribution, ecological impact, diseases caused, is introduced.

Symbiont Description:
Taxonomic details: genus species, basic details of its biology.

Host Description:
The host specificity of the symbiont. Include all hosts (intermediate, definitive, vectors, accidental, etc.)

Life Cycle: A basic walk-through of an entire generation of the parasite’s life cycle. Specific strategies employed by the symbiont or host that allow for efficient transmission will be described.

The consequences of this interaction in nature. (prevalence, distribution, disease, human interactions, economic impact, etc.)

An example of __________:
One aspect of the relationship that demonstrates a strategy or theory we talked about in class or was discovered from readings. (vector borne transmission, how complex life cycles can enhance fitness, how a parasite can alter society, etc.)

1. Zimmer, C. 2001. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures. New York: Free Press.
2. Combs, C. 2005. The Art of Being a Parasite. Chicago: The University of Chicago Press.