Tag: parasite

Posted in History & Literature

Rod Of Asclepius

Posted on by Jinavie

There are many symbols that represent the field of medicine such as a red cross or a stethoscope. However, one of the most famous symbols representing medicine and healthcare is the rod of Asclepius. This symbol is used in the logos of numerous medical associations and army medical corps. Those who do know of the rod may describe it as a staff with two wings and two snakes intertwining on it, but this is a common misconception. That symbol is called the caduceus and is actually the symbol of Hermes – the Greek god of messengers, merchants, markets, the high roads, gamblers and thieves. The misconception is very common and many medical associations use the caduceus as their symbol instead of the correct Rod of Asclepius.

The Caduceus

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The actual rod of Asclepius is much simpler looking, as it is simply a stick with one serpent intertwining it. The reason that it is associated with medicine and healthcare is that it was wielded by the Greek god Asclepius – the god of medicine and healing. Asclepius was the son of Apollo and had a particular interest in the human body and the healing of ailments. The ancient Greeks often referred to Asclepius in the field of medicine. In fact, the famous Hippocratic Oath originally began with the line “I swear by Apollo the Physician and by Asclepius and by Hygieia and Panacea and by all the gods…” (Apollo was the god of many things and medicine was one of his minor domains).

The rod of Asclepius

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So why does the rod of Asclepius have a serpent wrapped around it? In Greek mythology, it is said that Asclepius commanded many non-venomous snakes which he used in healing rituals. The snakes would crawl around the temple, living freely among the physicians and patients. A certain species of snake called the Aesculapian snake is considered to be the model for this story. The reason why the Greeks chose the snake as the animal of healing may be because snakes shed their skin periodically – symbolising rebirth and fertility. 

Another possible root of the symbol may be the traditional treatment for a certain parasitic infection. The Guinea worm (Dracunculus medinensis) is a parasite that lives under the skin, digging itself out through a painful blister when mature. As the blisters burn, the patient immerses the area in cold water to soothe it. The worm detects the change in temperature and releases its larva, completing its life cycle. The traditional treatment was to slowly pull the worm out of the skin, entwine it around a stick and leave it for a period of hours to weeks until it would be completely removed. The Greeks may have taken this image (of the worm wrapped around a stick) and applied it to the rod of Asclepius.

Posted in Psychology & Medicine

Sleeping Sickness

Posted on by Jinavie

A woman travelling in Africa is bitten by what appears to be a mosquito. She swats the insect and keeps on going about her journey. The next week, she finds that she has a small nodule where she was bit. She is also feeling slightly unwell, with fever and fatigue. Over the following two weeks, her fever worsens (coming and going intermittently) and she notices large lumps along the back of her neck. By this stage, she is experiencing muscle and joint pain as well. After returning home from her trip, she finds that her symptoms have not resolved. On top of her fever and pains, she begins experiencing headaches, mood swings, lethargy, confusion, clumsiness, delayed response to pain, sleepiness during the day and insomnia at night. She begins to worry that something is wrong, but she believes that it is a bad flu and does not see a doctor. Her symptoms worsen with time (sleeping up to 15 hours a day), until one day, she falls asleep and does not wake up. She is taken to a hospital, where it is discovered she is in a coma. She dies within a week.

This is the typical presentation of sleeping sickness, also known as human African trypanosomiasis. It is an infectious disease caused by a protozoan parasite called Trypanosoma brucei (comes in two types: T. brucei rhodesiense (East African type) and T. brucei gambiense (West African type)), which is transmitted by tsetse flies – a bloodsucking fly endemic to sub-Saharan Africa (there are also case reports of sexual transmission between people). When infected, the parasite rapidly proliferates in the patient’s bloodstream. It is not detected by the host immune system, thanks to a surface protein called VSG. This allows it to spread through the patient swiftly and silently via the circulatory and lymphatic systems. The early symptoms (intermittent fever, rash, lymph node enlargement), typically presenting about a week or two after infection, are due to the parasite spreading through the blood and lymph. As the infection spreads, the parasites begin to invade the central nervous system (although in the West African type of the disease, patients often die from the toxic effects of the parasite replicating in the blood before they reach this stage).

As the infection spreads through the CNS, it causes the neurological symptoms described in the case. The sleepiness (from where the disease gets its name from) worsens as the disease progresses, with patients finding it difficult to wake up in the morning, even sleeping for over 20 hours. The sleepiness is caused by a chemical called tryptophol, which is produced by the parasite. Essentially, the neurological symptoms appear as if the person’s brain is slowing down, until they fall into a coma, resulting in death without treatment (usually within 2~3 years since the infection).

Sleeping sickness is invariably fatal unless treated early. Once the patient reaches the second stage (neurological phase), treatment becomes very difficult. The current first line treatment is a drug called melarsoprol, which is a form of arsenic. Because of its toxic nature, it is extremely dangerous and there is around an 8% chance of the patient dying from side effects. Fortunately, there are less dangerous and more effective treatments such as eflornithine (which only works for the West African type) being developed.

Posted in Science & Nature

Slavemaker Ant

Posted on by Jinavie

Slavery is considered one of the most inhumane acts in humanity’s history, where a group of people enslave another group of people to do their bidding in harsh conditions. Slavery is an interesting concept as at the cost of other members of your species, you can greatly increase the productivity of your own society. Some may argue that only humans are evil enough to enslave their own kind, but there is one other species that enslaves other animals: ants.

Certain species of ants, known as slavemaker ants, are known to enslave entire ant colonies to do the bidding of their own colony. The way slavemaker ants enslave colonies is as follows. First, a pregnant queen ant lies in front of an enemy nest after mating and feigns death. Scouts from the nest carry the “body” back to their queen so that she may devour the fallen enemy. When the two queens are left in the same room, the queen slavemaker ant springs back to life and proceeds to eviscerate the other queen ant. She then rolls around in her remains to coat herself in pheromones – the substance through which ants identify each other. The ants of the colony now believe the queen to be their own queen and serve her and her eggs. When the brood fully matures (only soldier ants), they swiftly overrun the nest and completely enslave the colony, forcing them to fill the role of the worker ants, which the slavemaker ants lack.

Eventually, the original slaves die out and the colony becomes short on worker ants (as the queen only produces soldier ants). To overcome this issue, the colony sends out massive raiding parties to attack other colonies, after which the ants steal the eggs and larvae of the captured colony to breed them into new slaves. Interestingly, it has been observed that slavemaker ants tend to attack the most defended nests, knowing that they contain the most eggs and larvae. There are variations on how the army attacks and raids a colony depending on the species. Some choose to launch a full-on assault, decimating the colony and leaving only the eggs and larvae. Some secrete chemical gases that force the colony to evacuate, leaving their young behind in the rush. In some cases, a fertilised queen ant will sneak into a raid and kill the queen ant in the midst of the battle, commandeering whatever is left of the colony following the raid.

One difference between human and ant slavery is that slave ants are not aware they are slaves. Since they have been brought up since birth to work for the colony, they simply believe that they are worker ants birthed by the queen. Thus, they have no objections to serving the colony as to them they are merely fulfiling their objectives. 

This type of interaction between species is known as social parasitism, where one group benefits and survives at the cost of another group. Interestingly, “parasitism” also suggests that slavemaker ants cannot survive without their host. The reason being, slavemaker ants are so specialised in infiltrating and raiding other colonies that they cannot feed themselves or construct a colony by themselves. Even their mandibles are evolved into perfect killing machines, so much that they cannot use it to feed (slave ants have to feed them). In some cases, it has even been observed that slave ants had to carry their masters from one colony to another.

Slavemaker ants enslave not because they are tough or superior, but because they are desperate and have adapted to this unique form of surviving. Thus, if there was an Abraham Lincoln ant, he would certainly kill his colony within one generation.

Posted in Science & Nature

Red Queen’s Hypothesis

Posted on by Jinavie

In Lewis Carroll’s Through the Looking-Glass, there is a scene where the Red Queen says to Alice: “It takes all the running you can do, to keep in the same place”. Essentially, it means to spend all the effort you can just to keep the status quo. In life, there are so many times when it seems like you’re frantically running just to realise that no progress has been made. Interestingly, the same rule is seen in biology and evolution.

The simple rule of natural selection is that the best adapted species wins. Unfortunately, this means that no matter how well you are doing in the environment, as soon as another species becomes better adapted to a new change, you become the lesser species and eventually destroyed. To prevent this, a species must continuously evolve and adapt just to stay in the same position. Nature despises stagnancy and loves progress. For example, a predator always strives to evolve to better catch the prey while the prey evolves to avoid the predator. This cat-and-mouse arms race allows for continuous evolution and ever-improving fitness. This is the Red Queen’s Hypothesis.

A fascinating extension of the hypothesis is that it may be a cause for having sex. Sex is one of the most intuitive inventions of Mother Nature that allows for massive genetic variation. The Red Queen Hypothesis has been used to suggest that this may have evolved to speed up the process of evolution so that hosts could beat parasites in the ongoing arms race. The greatest act of love may simply be a mechanism for us to stay competent in this ever-changing world.

Posted in Psychology & Medicine

Toxoplasmosis

Posted on by Jinavie

There is a protozoan parasite called Toxoplasma gondii. This parasite infects many animals through an interesting route. 
The first victim is a mouse. An infected mouse loses its fear of cats, leading it to play fearlessly in front of one until it gets caught and eaten (was Jerry a mouse with toxoplasmosis?). It is unclear how it controls a more advanced animal’s brain, but thanks to this effect, Toxoplasma gondii can infect its intermediate host – a cat.
An infected cat starts excreting parasite eggs with its faeces. If a person forgets to wash their hands or eats food contaminated with cat faeces, they can be infected and become the final host for the parasite.

Usually, Toxoplasma gondii cannot overcome the healthy immune system, but it can infect those with a weaker immune system such as the elderly or pregnant women. Furthermore, it is part of the TORCH complex (toxoplasmosis, rubella, cytomegalovirus, herpes) – a group of infections that commonly cross over from the mother to the fetus in utero. Symptoms are normally flu-like, but if more severe it can cause dysfunction of the eyes, brain and other vital organs. Sometimes it lies dormant until the person’s immune system is weakened, whence it becomes active. Toxoplasmosis is also a possible cause of a miscarriage or infertility.

One fascinating symptom of toxoplasmosis is psychiatric disorders. Because Toxoplasma gondii can infiltrate the brain, it is known to cause depression or even schizophrenia. As cats are the most common intermediate host, cat owners are more susceptible to toxoplasmosis. Because of this, there is a theory that “crazy old cat ladies” are in fact toxoplasmosis patients.

Posted in Science & Nature

From Cell To Birth: Implantation

Posted on by Jinavie

When an egg is fertilised by the sperm, it is called a zygote. This zygote immediately starts to divide at an exponential rate, to achieve the feat of transforming from a single cell to a 3kg baby. The division and growth happens as the zygote slowly drifts towards the uterus, where it can secure itself.

30 hours after fertilisation, the zygote is now 2 cells.
72 hours, the zygote is now 16 cells.
96 hours, the zygote is now a ball of over 60 cells, and now called a morula.
108 hours, the morula has a cavity inside, and is called a blastocyst.
The blastocyst, essentially a shell of cells with a mass of cells at one point, hatches out of the zona pellucida as it is now much bigger.
To gain the massive amount of energy required for development, the zygote eats up simple sugars in the fallopian tube during its travel.

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As mentioned before, when pregnancy does not happen, the endometrium is shed and flushed out. To prevent this, the blastocyst secretes something called βhCG, keeping the corpus luteum alive, which secretes progesterone to maintain the endometrium. As the endometrium is the fertile “soil” where the embryo will grow, this is a vital step (βhCG is the hormone tested in a pregnancy test).
When the blastocyst reaches the uterus, it finds a safe spot on the endometrium, with the inner cell mass facing the wall. This is where implantation begins.

After clinging tightly to the endometrial cells, the blastocyst fuses some of its cells into a digging tool that can eat away at the endometrium. As it digests away the cells, the blastocyst slowly burrows in until it is completely embedded inside. Cells invade the hollowed space, firmly securing the blastocyst while destroying blood vessels and glands to release nutrients, securing a supply line. Now, it can start its rapid development into an embryo as it leeches away the mother’s nutrients.

A foreign body latching on to the host’s cells, digesting away tissue and leeching blood and nutrients – an embryo acts exactly like a parasite, to ensure that it can safely survive the 40-week gestation. In fact, an embryo can implant itself almost anywhere in the body, such as the fallopian tubes, ovaries or even the gut, as long as there is a secure blood supply. This is called an ectopic pregnancy, and can be an extremely dangerous scenario to both the mother and developing fetus.

(Full series here: https://jineralknowledge.com/tag/arkrepro/?order=asc)