By Steven Ryan
Imagine you are at the Amazon River and decide to go for a swim. Just before you jump in the water you hear a bloodcurdling scream. Your mind would automatically think of crocodiles or piranha, but instead out of the water runs a man screaming like a little child about a leech. You laugh thinking how bad could a single leech be. Taking a quick look at what is attached to his leg you see said leech, but this is no normal leech. It is an Amazon Giant Leech.
The Amazon Giant Leech is quite possibly the world’s largest blood sucking leech. They have quite a lot of competition for this title with the 700 to 1000 other species of leeches, but this is fairly impressive. It belongs to the Phylum Annelida and the Family Glossiphoniidae, meaning that it is a jawless freshwater leech that can grow to 450 mm (17.7 in) in length and 100 mm (3.9 in) in width. They live from the mouth of the Amazon river north to Venezuela and the Guianas. An adult is a greyish-brown colour, as opposed to juveniles, which do not have a uniform colour, but rather a noncontinuous stripe and patches of colour.
So what is the poor guy doing to do about his problem? The common knowledge for removing a leech is that you pour some salt on it or burn it off. This is wrong and an overall bad idea. The use of fire or salt on a leech causes it to drop off, sure, but it also cause it to vomit up its meal into the open wound which may cause an infection. Some advice most often given is to just leave it till it is full and falls off. That might be fine for a regular leech but this is a freaking big leech. Simply sliding a fingernail under the anterior sucker and the leech will let go and take its 10cm long proboscis with it.
What is a proboscis you ask? Unlike the jawed leeches that bite using two or three rows of jaws(depending on the species) set in either a V for the two jawed leeches or an upside down Y fashion for the three jawed leeches, this particular leech has a hypodermic needle lying in wait inside its mouth. When prey comes within range they extend their proboscis like a spear. Once the leech is attached to the prey, the proboscis then functions much like a straw that releases anticoagulants and starts to suck up the blood at a rate of 0.14mL per minute and up to 15 mL (Sawyer et al. 1991). What does this mean for medicine?
Leeches have been used since medieval times to remove blood. The lack of medical knowledge led to the belief that leeches were a cure all. Leeches were used to treat a variety of disorders, ranging from tuberculosis to epilepsy and rheumatism. This of course was wrong and the belief came from not knowing about bacteria, and a lack of understanding about the human body.
In recent time the leech has made a comeback in the medical field in the use of plastic surgery and micro surgery. There is even some evidence that the Amazon Giant Leech contains within its body various types of proteinase inhibitors that may be able to inhibit the spread of lung tumours, although this has not been proven by direct evidence (Gasic et al. 1983).
The Giant Amazon Leech was thought extinct because a specimen had not been collected since 1893. In the 1970’s, Dr. Roy Sawyer rediscovered two adult H. ghilianii in a pond in French Guiana. How many are there now? Well a single brooding H. ghilianii produced 366 hatchlings. What were the chances that the two leeches found by Dr Sawyer were a mating pair? Extraordinarily good since H. ghilianii are hermaphrodites and as such are both male and female. Sexual maturity was found to relate not so much to age as to weight. The male reproductive system matures at 3-5 grams and the female system at 10 grams (Sawyer et al. 1981)
So where does that leave this amazing creature? Grandma Moses (pictured above) had managed to produce over 750 offspring within the first three years of breeding. More than 46 medical, neurological and natural history research publications were based on data from specimens reared at the University of California-Berkeley breeding colony (Invertebrates 2014). So things are looking up for H. ghilianii. Maybe one day you will have to worry about the Amazon Giant Leech while swimming like the poor fellow in the hypothetical situation at the start of this article.
Gasic, G. I., Viner, E. D., Budzynski, A. Z., Gasic, G. P. (1983). Inhibition of lung tumor colonization by leech salivary gland extracts from Haementeria ghilianii. Cancer Res. 43:1633–36
Invertebrates [Internet] (2014). Smithsonian National Museum of Natural History. Available from: http://invertebrates.si.edu/Features/stories/haementeria.html Accessed April 1, 2015
Sawyer, RT,Lepont, F., Stuart DK, and Kramer AP. (1981). Growth and reprodution of the giant Glossiphoniid leech Haementeria ghiliannii. Biol. Bull. vol. 160: 322 – 331.
Sawyer, RT, Jones CP, and Munro R. (1991). The biological function of hementin in the proboscis of the leech Haementeria ghilianii. Blood Coagul. Fibrinolysis. 2: 153–159.