Review by Josh Sutton
Parasitology, the study of parasites and the interactions that they have with their hosts, is an often overlooked area of biology. Parasite infections are common worldwide and cause diseases such as malaria, trypanosomiasis (sleeping sickness), toxoplasmosis, elephantiasis and onchocerciasis (river blindness). Because of the severity of these diseases and the suffering that they cause, parasitology is an important area of research.
Over recent years, presenter Michael Mosley has carved out a documentary niche, in which he uses himself as a human guinea pig for a variety of experiments. In this insightful programme, Mosley infests himself with a variety of parasites – including tapeworms, head lice, and leeches. Plasmodium, the genus causing malaria, is covered well in this documentary (at 25 mins until 29:45). The complex life cycle of the parasite and how it interacts with both the human host and the mosquito vector, is well explained. The microscopic images shown are also a valuable addition to the documentary, clearly showing the effect of the Plasmodium on the body’s red blood cells.
Not all parasite infections cause diseases as severe as malaria. Infection by a tape worm can cause relatively mild symptoms such as vomiting, muscular pain and diarrhoea, and in developing countries can also worsen the effects of malnourishment. Tapeworm is the main focus of the documentary (this 17 minute clip http://bobnational.net/record/285488 picks out just the relevant sections) . Mosley infects himself with tapeworms to show the life cycle of the organism and the various effects it has on the body. He also considers the benefit to the parasite of infecting a host. We follow the infection from a cow in Kenya, to infecting Mosley (via ingestion of the cyst form) and then through to the way it exerts an effect on his body, as well as how it will reproduce if given a chance.
Toxoplasma gondii is also covered in the programme (see clip http://bobnational.net/record/285497), including demonstration of the ability of a parasite to benefit by moderating the behaviour of a host. As well as affecting the host’s immediate behaviour, it is suggested that evolution with parasites has helped humans to develop a sense of disgust, helping us to avoid foods that would lead to illness (http://bobnational.net/record/285495), improving our chance of survival.
While this documentary covers the helminths (tape worms, hook worms etc) and the ectoparasites (ticks, leeches and lice) well, it does not cover the amoeba parasite Acanthamoeba at all. Acanthamoeba causes keratitis (infection of the cornea) and is of growing concern as an infection of contact lens users, as poor lens hygiene can lead to direct infection of the eye. It also does not cover Entamoeba histolytica, an amoeba that causes intestinal infections, resulting in amoebic dysentery. Both of these parasites could be read up on after watching the documentary, for more information on different types of parasite.
Of particular interest in this documentary is a clip where the hygiene hypothesis is discussed. The hygiene hypothesis is the suggestion that a failure to expose children to antigens of pathogens, commensal bacteria and parasites has led to the increased development of allergies, as the immune system has not properly developed. In one section (see clip here http://bobnational.net/record/285501) Daniel, a man suffering from Crohn’s disease, gives anecdotal evidence about how he has treated himself by infecting himself with hookworm he bought over the internet. This is then followed by a scientist explaining why this is dangerous and that rigorous studies need to be performed before people undergo such radical treatment. This could be used as part of a discussion on experimental design, explaining why such anecdotal evidence does not pass scientific scrutiny and what kind of experiments would need to be performed to prove the safety of such a practice and if it is even effective to treat allergies.
Overall, this documentary is an excellent introduction to parasitology and covers the main areas well, although it would be beneficial to follow up with reading up on some of the amoebic pathogens.