One in three people are infected with Toxoplasma parasite – and the clue could be in our eyes

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, an estimated 30-50% of people are infected with Toxoplasma – and infections could be on the 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%. 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 Cats are 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 thereafter, the animals are slaughtered for meat. Humans can become infected by eating this meat, or by eating fresh produce, or by drinking water contaminated by cats. It is also possible for a woman first infected during pregnancy to transmit the infection to her unborn child.

Although Toxoplasma infection is extremely common, the most important health statistic is the rate of disease caused by the infection, called toxoplasmosis.

How it affects the eye Toxoplasma loves the retina, the multi-layered nerve 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 to be one in 150 Australians. This may seem surprisingly common, but it’s consistent with how people get Toxoplasma.

In addition to pet cats, Australia has a huge population 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 needed, ideally with the pupils dilated.

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 its 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, most often a combination of anti-inflammatories and antiparasitics is prescribed.

Stopping the spread of Toxoplasma infection is not curable, but it can be prevented. Meat sold in Australian supermarkets may harbor Toxoplasma.

Cooking the meat to an internal temperature of 66 degrees Celsius 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. Gloves should be worn when changing kitty litter and hands washed 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 control Toxoplasma infections in this country.

(This story has not been edited by the Devdiscourse team and is auto-generated from a syndicated feed.)

Leave a Comment