Toxoplasma gondii is probably the most successful parasite in the world today. This microscopic creature is capable of infecting any mammal or bird, and people on all continents are infected.
Once infected, a person carries Toxoplasma for life. So far, we don’t have a medicine that can eradicate the parasite from the body. And there is no vaccine approved for use in humans.
Worldwide, it is estimated that 30-50% of people are infected with Toxoplasma – and infections could rise in Australia. A survey of studies conducted at blood banks and pregnancy clinics across the country in the 1970s put the infection rate at 30 percent.
However, a recent community survey from Western Australia found that 66% of people were infected.
The disease caused by this parasite can scar the back of the eye. Our new research looked for signs of disease in otherwise healthy people and found that a significant number bore the mark of Toxoplasma.
We don’t just get it from cats
The cat is the main host of Toxoplasma.
Cats catch the parasite when they eat infected prey. Then, for a few weeks, they pass on large numbers of parasites in their droppings in a form that can survive for long periods in the environment, even in extreme weather.
When feces are ingested by livestock during grazing, the parasites lodge in the muscle and survive there after the animals are slaughtered for meat. Humans can become infected by eating this meat, or by eating fresh produce or drinking water contaminated by cats.
It is also possible for a woman first infected during pregnancy to transmit the infection to her unborn child.
While an infection with Toxoplasma is extremely common, the most important health statistic is the rate of illness caused by the infection, called toxoplasmosis.
How it affects the eye
Toxoplasma really loves the retina, the multi-layered nervous tissue that lines the eye and generates vision. The infection can cause recurrent attacks of retinal inflammation and permanent retinal scarring. This is called ocular toxoplasmosis.
Contrary to much written about ocular toxoplasmosis, medical research shows that this disease usually affects healthy adults. However, in older people or people with weakened immune systems, or when contracted during pregnancy, they can be more serious.
An active attack of inflammation causes “floaters” and blurred vision. As inflammation progresses to scarring, there may be permanent loss of vision.
In a study of patients with ocular toxoplasmosis seen at a large eye clinic, we measured reduced vision below driving level in more than 50% of eyes, and 25% of eyes were irreversibly blind.
How many eyes?
Ophthalmologists and optometrists are familiar with the management of 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.
We wanted to study the prevalence of ocular toxoplasmosis in Australia, but knew it would be difficult to secure funding for a major survey of this neglected disease.
So we used the collected information for a different purpose: As part of the Busselton Healthy Aging Study, retinal photographs were taken of over 5,000 baby boomers (born between 1946 and 1964) living in Busselton, Western Australia.
The photographs were collated to search for other eye diseases, macular degeneration and glaucoma.
Looking at these retinal photographs, we estimated the prevalence of ocular toxoplasmosis at 1 in 150 Australians. It may seem surprisingly common, but it’s consistent with how people catch Toxoplasma.
In addition to pet cats, Australia has huge populations of feral cats. And Australia is home to plenty of agricultural land, including more than 50% of the world’s organic farming area.
More importantly, many Australians like to eat their red meat rare, putting them at real risk.
How the condition is treated
To diagnose ocular toxoplasmosis, an examination of the retina is necessary, ideally with dilated pupils.
The retinal lesion is easy to spot, due to the way Toxoplasma activates retinal cells to produce certain proteins, and an ophthalmologist or optometrist can immediately recognize the appearance. 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 control the problem, which takes a few months. However, a combination of anti-inflammatory and antiparasitic drugs is usually prescribed.
Stop the spread
Toxoplasma the infection is not curable, but it can be prevented. Meat sold in Australian supermarkets could harbor Toxoplasma. Cooking the meat to an internal temperature of 66°C or freezing it before cooking are ways to kill the parasite.
Fresh fruits and vegetables should be washed before eating, and drinking untreated water (such as that coming directly from rivers or streams) should be avoided. Wear gloves when changing cat litter and wash your hands afterwards.
The World Health Organization and other international and national health bodies promote an approach called One Health for diseases that cross humans, animals and their environments. It involves different sectors working together to promote good health.
Now that we know how common ocular toxoplasmosis is in Australia, there is real justification for harnessing One Health to combat Toxoplasma infections in this country.
Justine R. Smith, Professor of Eye and Visual Health, Flinders University and João M. Furtado, Assistant Professor of Ophthalmology, Universidade de São Paulo.
This article is republished from The Conversation under a Creative Commons license. Read the original article.