Friend or Foe

Thursday, 07 March 2019


Medico-Chirurgical Hall

Professor Elisabeth Innes MBE, Principal Scientist and Director of Communication, Moredun Research Institute, Edinburgh

Friend or Foe - the parasites that live inside us

Scottish doctors, scientists and explorers discovered many of the most important parasitic diseases and pioneered research to find treatments and prevention strategies. This talk will look at examples of different host parasite relationships illustrating some that can be deadly, those that live inside us and may change our behaviour to how parasites can be good for us.

Notes

Meeting and Lecture held on Thursday 7 March 2019

The President welcomed everyone to the meeting and apologies were noted. He also noted that sadly there had been several deaths of past members of the Society; Antoine Ah-See, Ann Brunt, James Webster and George Taylor.

The President highlighted forthcoming events, a WW1 commemoration in May and also Famous for Five Minutes in May. He reminded members of recent requests for nominations for the President’s Medal, the next President-Elect and new Council members.

The President then introduced the speaker for the evening, Professor Elisabeth Innes from the Moredun Research Institute in Edinburgh.

She was brought up in Aberdeen, attending Aberdeen Grammar School. Her father was a Consultant Forensic Psychiatrist here. Professor Innes went on to study immunology at the University of Glasgow and completed a PhD in tropical veterinary medicine in Edinburgh, with a special interest in parasites. Parasites have continued to her research interest throughout her career.

Parasites are organisms which live inside or attach to humans or other animals, gaining nutrition and energy from their host. A well-adapted parasite will not generally kill its host. However, people moving to a new area and encountering different parasites are more vulnerable.

Professor Innes indicated that her talk would explore examples of where the host parasite relationship may be dangerous, harmless and beneficial.

Historically, several Scottish doctors went abroad to work in tropical disease medicine and many are noted in the book, “The Scottish Encounter with Tropical Disease”.

David Livingstone travelled 30000 miles across Africa on foot. At the time, 1 in 10 missionaries died, usually of malaria or sleeping sickness. He contributed to the effective treatment of malaria, using quinine derived from the bark of the Cinchona tree. Synthetic derivatives e.g. chloroquine was used in the treatment of malaria, but parasites readily develop resistance. Artemisinin is currently effective.

Ronald Ross (Nobel Laureate 1902) demonstrated the link between malaria and mosquitos. He realised that swamp drainage was important. He also noted parasites growing in blood cells. Malaria still afflicts approximately 500 million people in tropical areas of the world. Charities such as the Bill and Linda Gates Foundation invest in preventive measures such as bed nets and the development of more effective drugs for prevention and treatment. As yet, there is no vaccine available.

David Bruce identified trypanosomes as the cause of sleeping sickness in humans and animals, and he made excellent drawings of the organisms. The disease is transmitted by the tsetse fly; the organisms proliferate in the blood stream and invade the brain, eventually affecting neurological function and resulting in coma and death if not treated. The treatment is not without toxicity, as it is arsenic based. 

Patrick Manson had an interest in parasitic infection. He demonstrated that the worms responsible for lymphatic filariasis were transmitted by mosquitos. Lymphatic filariasis (elephantiasis) causes a build-up of lymph and limb deformities. Approximately 120million people in 80 countries are affected. He set up a medical practice in Taiwan and a medical school in Hong Kong, as well as founding the London School of Tropical Medicine. He is known as “the father of tropical medicine”.

Professor Innes went on to speak about Toxoplasma gondii, the main focus of her studies throughout her career. It is a very successful parasite and approximately 70% of the population has the parasite in their brain. It lives in all warm-blooded animals and can produce a wide spectrum of clinical signs, depending on the adaptation of the parasite to the host.

The cat is its definitive host (where it undergoes a sexual cycle) and other animals are secondary hosts (no sexual cycle). It is known that it can cause harm to a human foetus. It is particularly harmful to sheep; pregnant ewes catching toxoplasma are likely to abort. 24% of ovine abortions are due to toxoplasma.

The WHO has identified toxoplasma as being a very important food-borne disease globally. Congenital infection results in eye disease, brain damage and learning disabilities. Incidence is 5 per 100,000 births in the UK but significantly higher in Brazil at 5 per 1000 births. Toxoplasma infection causes even greater problems in immunocompromised patients.

Cats shed millions of eggs in to the environment, which can live in the ground for months. If ingested, these mediate an immune response, with development of cysts containing the parasite. Infection in sheep, cattle and pigs can be transmitted to humans via ingestion of undercooked meat.

Investigation of sheep flocks across Scotland has shown 52% sero-prevalence. Every flock across Scotland is affected by toxoplasma. As an infected pregnant sheep fights the infection, there is resultant necrosis of the placenta and abortion. Following infection in pregnancy, both sheep and humans develop good immunity and subsequent pregnancies are okay. A vaccine is now available for ovine toxoplasma infection (which also protects against tissue cysts) and a similar vaccine may be developed for human use in the future.

Blood donors in Scotland (aged 20-60 years) show 12% sero-prevalence of toxoplasma antibodies. The major route of transmission to humans is via undercooked meat, particularly from outdoor reared animals. It is less problematic with pig meat and chicken because most people tend to cook these well. However, a number of people prefer to eat cattle meat rare, making cattle an important transmission animal. Despite the low incidence of congenital toxoplasma infection in the UK, the impact is high when measured as DALYs.

There are steps which can be taken to prevent toxoplasma infection; biosecurity on farms, producing a vaccine for food animals and cats (as well as sheep), freezing meat, cooking meat well and curing/salting meat, (which kill the organism) and educating farmers, schoolchildren and chefs.

Professor Innes concluded her talk by giving some examples of how we might be helped by parasites. Worms have evolved over one billion years to regulate our immune responses and enable them to live within our intestines. Without worms, our immune systems can over-react to harmless substances. In developed countries, improved hygiene standards and public health measures have reduced worm burdens in the population, and there has been an increased prevalence of allergic disease. New therapies, based on worms, have been trialed to aid treatment of allergic and auto-immune diseases such as hay fever, eczema, asthma, inflammatory bowel disease and MS. Also, parasite induced immunomodulation may help patients to tolerate a new allograft.

The evening concluded with Professor Innes answering questions and receiving thanks from the President.

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