The Toxoplasma gondii is probably the most successful parasite in the contemporary world. This microscopic creature is capable of infecting any mammal or bird, and people on all continents are infected with it. affected. Once infected, a person is a carrier of the Toxoplasma for life. So far, no medicine can eradicate the parasite from the body. And there is no vaccine approved for use in humans.
Where do you think that 30 to 50% of the world’s population carries the Toxoplasma – and infections could progress in Australia. A review of research conducted at blood banks and pregnancy clinics nationwide in the 1970s estimated the infection rate at 30%. However, a recent community study in Western Australia found that 66% of people were infected. In comparison, we are talking about a prevalence of 60% in the Inuit communities of northern Quebec, compared to 15% in the rest of Canada.
The disease caused by this parasite can leave scars on the back of the eye. Our new study aimed to look for signs of disease in otherwise healthy people, and found that a significant number of them bore the mark of the Toxoplasma.
Cats aren’t the only culprits
The cat is the primary host of Toxoplasma.
The parasite takes hold in cats when they eat infected prey. Then, for a few weeks, their faeces contain a large number of parasites in a form that can survive for long periods in the environment, even under extreme climatic conditions.
When faeces are ingested by grazing cattle, the parasites lodge in the muscle and survive there after the animals have been slaughtered for meat. Humans can become infected by eating this meat, eating fresh fruits and vegetables, or drinking water contaminated by cats. It is also possible for a woman initially infected during her pregnancy to transmit the parasite to her unborn child.
Although infection with Toxoplasma is extremely common, the most important health statistic is the attack rate of the disease, toxoplasmosis, caused by the infection.
How the eye is affected
The Toxoplasma particularly likes in the retina, the multi-layered nerve tissue that lines the eye and generates vision. The infection can cause recurrent attacks of inflammation of the retina and permanent retinal scars. This is called ocular toxoplasmosis.
Contrary to what you may read about ocular toxoplasmosis, medical research shows that this disease usually affects healthy adults. However, in older people or those with weakened immune systems, or when contracted during pregnancy, it can be more serious.
An active attack of inflammation causes “floaters” and blurred vision. When inflammation progresses to scarring, permanent blindness may occur.
In study in patients with ocular toxoplasmosis followed at a large eye clinic, we recorded vision reduction below that required for driving in more than 50% of eyes, and 25% of eyes showed irreversible blindness .
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How many eyes?
Ophthalmologists and optometrists are familiar with ocular toxoplasmosis. But the extent of the problem is not widely recognized, even by the medical community. The number of Australians with ocular toxoplasmosis had never been measured, until now.
Our goal was to study the prevalence of ocular toxoplasmosis in Australia, but we knew it would be difficult to secure funding for a major survey of this little-known disease. We therefore used information collected for a different purpose. As part of the study Busselton Healthy Ageing Study, retinal photographs were taken of more than 5,000 baby boomers (born between 1946 and 1964) living in Busselton, Western Australia. These photographs have been collected to look for other eye diseases such as macular degeneration and glaucoma.
By analyzing these retinal photographs, we have valued the prevalence of ocular toxoplasmosis at 1 in 150 Australians. This may come as a surprise, but this fits well with the way people contract the Toxoplasma.
In addition to domestic cats, Australia has huge populations of feral cats. And the country is home to a lot of agricultural land, which accounts for more than 50% of the global organic farming area.
More importantly, many Australians like to eat their rare red meatputting them at serious risk.
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The way to treat the condition
To diagnose ocular toxoplasmosis, an examination of the retina is necessary, ideally with dilated pupils.
The lesion is easy to spot, due to the way the Toxoplasma activates retinal cells to produce certain proteins. An ophthalmologist or optometrist can immediately detect its onset. Often a blood test is also done to establish the diagnosis.
If the condition is mild, the doctor may let the body’s immune system deal with the problem, which takes a few months. However, it is prescribed usually a combination of anti-inflammatory and antiparasitic drugs.
Stop the spread
The infection by the Toxoplasma cannot be cured, but it can be prevented. Meat sold in Australian supermarkets can host the Toxoplasma. Cooking the meat to an internal temperature of 66 °C or freezing it before cooking are all means of kill the parasite.
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Fresh fruits and vegetables should be washed before consumption and drinking untreated water (such as that coming directly from rivers or streams) should be avoided. It is advisable to wear gloves to change the cat litter, and to clean your hands afterwards.
The World Health Organization and other international and national health bodies promote an approach called one health to combat diseases that affect humans, animals and their environment. It requires the collaboration of different sectors to promote good health. Now that we know how common ocular toxoplasmosis is in Australia, there is every reason to harness the One Health approach to tackling ocular infections. Toxoplasma in this country.