The good parasites

A parasite lives on or inside its host organism in a very unequal relationship.  The parasite takes all of its food from its host and doesn’t give anything back so quite often the parasite makes the host quite ill or causes discomfort.

Are there any good parasites - any that actually have a benefit?  The blood-sucking leech is a parasite, it attaches to its host (animal or human) and feeds on the blood, but it has been and still is very important in medicine! 

Blood-sucking leeches attach to their host and feed until they become full.  They then fall off to digest the blood they have taken.  Leeches are very clever – they have an anaesthetic that stop the host from feeling the leech and they have an anti-clotting agent in their saliva that lets the blood flow more freely.  Leeches from the wild were used to remove poison from the blood but now they grow and live in special laboratories.  These modern leeches eat unwanted blood, numb pain or reduce swelling and keep blood flowing in wounded limbs.  This keeps the limbs alive and allows doctors to fix or reattach them!

Another parasite that features very highly on the ‘yuck’ scale but that actually does good is the maggot (a baby fly).  Maggots, like leeches, grow and live in special laboratories and are used to clean up wounds that are infected or that are not healing well.  Maggots only eat dead skin and tissue so they get rid of the diseased part, leaving the healthy part behind.  Many people are very grateful to these wriggly guys and to leeches as they often save a limb or body part from being amputated!

Another kind of good parasite are fungi!  Fungi cannot make their own food and grow on plants, animals, humans, dead and decaying organic matter, anywhere, in fact, where it is warm and damp!  They get their food by making enzymes that digest food from the surface they are growing on and absorbing the digested nutrients through their cell walls.  Fungi mainly absorb water and digest sugars and starches which they use to grow. 

Some fungi can be very dangerous but the best known fungi, the mushroom, are really good to eat!  Other fungi, like the yeast, Saccharomyces cerevisiae is used in the process of fermentation to make bread.  Yeasts are also involved in the fermentation of wines and beers and in brewing soy sauce which is used in Chinese cooking.  Blue chesses like Cashel blue or Roquefort are injected with certain kinds of fungal spores.  The mold that grows from the fungal spores gives the blue cheeses their colour and yummy taste.  Don’t worry - these fungal spores and molds are not toxic to humans, so they won’t make you sick.

There are some fungi that are used in medicine.  They kill bacteria that invade your body and produce antibiotics like penicillin.  Antibiotics made from fungi are used to treat nasty diseases like tuberculosis (TB) and leprosy.  Not only that, but they can be used to fight off insects, pests and even other fungi that grow on plants!

Fungi, along with bacteria, are one of the best decomposers of organic material.  Without them, dead plants and animals would just hang around and the nutrients from the dead material would not return to the ground.  Other plants, animals and micro-organisms that rely on that food would also die and the delicate balance of the ecosystem would be lost.  So next time you are out for a walk and see mushrooms, do your best to help to spread these ‘fun guys’ around and help them to help you!

So, not all parasites are bad, but it can be very difficult to find a good one.  Make sure you use an expert to figure out which ones are your friends!