What is Pythium Keratitis?
Pythium is a water parasite that’s like a fungus, and is also referred to as “parafungus” or “fungus-like organism”. The first known case of a Pythium infection was documented by British veterinarians in 1884.
This parasite can infect both animals and humans, leading to systemic (affecting the whole body) and eye infections. It is often found in water bodies, particularly in tropical, subtropical and temperate climates. It is more frequently found in males, especially those who work in fields. The symptoms of a Pythium infection are very much similar to a fungus condition known as fungal keratitis and include dull stromal infiltrate (a cloudy area in the cornea), feather-like edges, small separate sores, endothelial plaque (deposits under the cornea), hypopyon (pus in the eye), and possible puncture of the cornea.
Since the parasite’s structure and growth are similar to a fungus, it’s typically identified by the formation of zoospores (spore-like cells) when grown in a scientific culture. To treat Pythium infections, antifungals, antibacterials, and a special kind of adhesive called cyanoacrylate glue are used. Antibacterials like linezolid and azithromycin have shown to work well against the parasite in lab tests, and so are often used as the first line of treatment for Pythium infections of the eye.
In stubborn cases that do not improve, a surgical procedure known as therapeutic keratoplasty (which replaces a portion of the cornea) may be necessary. Due to the parasite’s quick growth, threat level, the limited ways to precisely diagnose it everywhere, the limited effect of some current treatments, and the high frequency of the infection’s return, diagnosing and treating Pythium infections remains a puzzle and a hurdle for many eye doctors.
What Causes Pythium Keratitis?
Pythium is a type of parasite, which was previously categorized as a fungus. While most species of Pythium affect plants, one particular kind called Pythium insidiosum can harm both humans and animals, causing a disease known as pythiosis. Over 120 types of Pythium have been found across the globe. Pythium insidiosum, in particular, can cause a severe eye condition in humans that might result in loss of vision.
The forms of Pythium that have been observed in humans affect different parts of the body, including the eyes, skin, and blood vessels, and can spread throughout the body. The symptoms can manifest as skin ulcers and lumps on the skin, face, arms, and under the skin. When it affects the blood vessels, it could result in aneurysms (swellings in the wall of an artery), thrombosis (blood clots), and vasculitis (inflammation of blood vessels).
Systemic associations, or conditions that might occur with Pythium, include Thalassemia (a blood disorder that reduces the production of hemoglobin), Paroxysmal nocturnal hemoglobinuria (a rare disease where blood cells break down earlier than normal), aplastic anemia (when the body stops producing enough new blood cells), Chronic arterial insufficiency syndrome (not enough blood reaching certain parts of the body), and Cavernous sinus thrombophlebitis (a blood clot in the cavernous sinus, a large vein at the base of the brain).
According to previous studies, Pythium is often associated with injuries from mud, grass, soil, clay, or a stick in the eye. It also appears to be more common among people who work in water-based fields.
Risk Factors and Frequency for Pythium Keratitis
The first case of a full-body infection caused by pythiosis, a serious disease, was documented in 1884 by British veterinarians studying horses. Various countries, including Thailand, the USA, China, Israel, Australia, and India, have seen severe eye infections leading to potential blindness from this disease.
The first human with a full-body pythiosis infection was reported in Thailand in 1985. In 1988, the first case of Pythium keratitis, an infection of the cornea, was documented and since then, there have been extensive studies conducted worldwide. This disease can occur in animals that live in tropical, subtropical, and temperate climates, with instances reported in Australia, Argentina, Brazil, Costa Rica, India, and Indonesia.
Research on the occurrence and spread of Pythium keratitis is limited because this organism is rare.
- The disease can affect people of all ages, but is more common among students and software professionals.
- In older age groups, it’s mostly seen in males who work outside.
Signs and Symptoms of Pythium Keratitis
Patients with Pythium keratitis, an eye infection, often have symptoms such as pain, eye redness, sensitivity to light (photophobia), blurred vision, irritation, tears, and sometimes, discharge. In some cases, prior incidents like stick injury, mud injury, dust fall, clay injury, or contact lens use might have occurred. However, in some instances, there is no clear cause of the infection.
Common findings when examining the front part of the eye are similar to those seen in fungal corneal ulcers. These can include:
- Swelling of the eyelid (lid edema)
- Eye twitching (blepharospasm)
- Eye congestion (conjunctival congestion)
- Discharge
- Epithelial defect
- Stromal infiltrate
- Feathery margins
- Satellite lesions
- Stromal edema
Other potential findings may resemble conditions such as corneal melt, descemetocele, endothelial plaque, hypopyon, anterior chamber exudates, ring infiltrate, Wessel’s immune ring, and corneal perforation.
Typical signs that identify Pythium keratitis include infiltrate in the stroma with jagged edges, multiple lesions, tentacle-like projections, furrowing on the periphery, early spreading towards the edge of the cornea (limbus), and an increased frequency of other eye conditions.
Rarely, there are symptoms that resemble Acanthamoeba keratitis, which includes radial keratoneuritis with stromal infiltrates. This generally happens with mixed infection of Acanthamoeba and Pythium, particularly in contact lens users. A few signs might also compare to atypical Mycobacteria, with symptoms such as epithelial breach, greyish white stromal infiltrate, dryness, a “cracked windshield” appearance of the infiltrates, stromal edema, and folds in the Descemet’s membrane.
Testing for Pythium Keratitis
If you are suffering from Pythium keratitis, a disease that affects the cornea (the clear, front surface of your eye), the medical professional may want to collect a sample from your eye. This is usually done under local anesthesia with special medical tools like a Kimura spatula or a Bard-Parker blade. Once they have collected the sample, they examine it under a microscope using special dyes that highlight the potential presence of the Pythium fungus.
Under the microscope, the fungus can be seen as thread-like cells with a specific branching pattern. Along with this, part of the collected samples may be used to grow fungus colonies in a controlled environment such as nutrient-rich agar plates. Pythium typically forms white creamy colonies and produces spores that have small bubbles in them.
Once the colonies grow, they would be confirmed using a technique called the leaf incarnation method. There would also be an examination done on microscopic slices of the collected samples, using a variety of colorful dyes that bind specifically to characteristics of the Pythium fungus.
A blood test could also be carried out to look for the presence of antibodies against Pythium in your body; this is known as serological analysis. A range of tests, like immunodiffusion, ELISA, and western blot, could be used. While immunodiffusion has a 61% chance of detecting the disease, ELISA tests are reported to be very accurate and have a 100% chance of detection.
A molecular technique called a polymerase chain reaction (PCR) test may also be used. This particular test tries to spot the Pythium’s genetic material in the sample, which can help in making a quick and accurate diagnosis. Additionally, in-vivo confocal microscopy (IVCM), a special kind of microscope that allows doctors to observe the eye’s cells in detail, might also be used. Through this, the fungus would appear as beaded or thin reflective lines.
An ultrasound could also be done to check for complications associated with the disease like if the retina (the light-sensitive layer at the back of your eye) is detached, or if there is an infection and inflammation within the eye.
Treatment Options for Pythium Keratitis
Previously, Pythium was grouped with fungal species, so antifungal medicines were the first line of treatment for Pythium keratitis, an infection of the cornea (the clear, outermost layer of the eye). However, recent findings have shown that these antifungal medicines do not effectively treat Pythium keratitis. Still, they can play a role in initial management since it’s difficult to distinguish Pythium from real fungi before getting the results from lab tests.
Today, doctors treat Pythium keratitis with antibacterial eye drops. These often include linezolid and azithromycin, due to their easy availability and low risk of harmful side effects. They are used in small quantities throughout the day, with their use scaled back based on how a patient reacts to them. It’s advised to be cautious in this process, as overuse can lead to eye damage. Antibacterials have proven to be more effective than antifungal medicines for treating Pythium keratitis.
Surgery, in the form of therapeutic keratoplasty (TPK), is frequently needed due to the aggressive nature of the microorganism causing Pythium keratitis. This disease tends to spread quickly, and medicines often fail to control it. If the condition does not improve with maximum medical therapy for up to two weeks or complications like inflammation of the eye tissues, thinning or bulging of the cornea, or perforation of the cornea develop, an early TPK is usually recommended. Here, the diseased cornea is replaced with a healthy one.
In severe cases where the infection progresses and affects other parts or all parts of the eye, evisceration or enucleation (removal of the eye’s contents or the entire eye) might be needed.
There are other alternative treatments available as well. One of them is cryotherapy, which uses extremely cold temperatures to kill the harmful cells. This treatment also involves the use of ethanol, an agent that disables the harmful cells’ living processes. Cyanoacrylate glue along with a bandage contact lens can also be used for those with initial stages of corneal melting or perforation. The glue not only seals the damage but also has antibacterial properties that can prevent further infection.
What else can Pythium Keratitis be?
When considering different forms of keratitis (inflammation of the cornea), professionals would likely look at the following:
- Fungal keratitis (caused by a fungus)
- Bacterial keratitis (caused by bacteria)
- Atypical Mycobacterial keratitis (caused by a specific type of bacteria)
- Acanthamoeba keratitis (caused by a parasite)
- Necrotizing viral keratitis (caused by a harmful virus)
What to expect with Pythium Keratitis
The outcome of your condition depends on several factors: the size and depth of the infiltrate (an area of cells or tissues that have been unlawfully entered), its extent, any associated complications, when treatment is started, and follow-ups. If you have early superficial stromal infiltrates (a group of inflammatory cells in the eye not affecting the main line of vision), and if you get treated early with a regular follow-up, it’s likely that your sight will recover quite well.
However, if you have full-thickness infiltrates (infiltrate that reaches the full thickness of your cornea), a corneal perforation (a hole in the cornea of the eye), and anterior chamber exudates (inflammatory debris in the front part of the eye), you may need an early keratoplasty. This is a type of cornea transplant procedure that helps prevent the spread of infection to the back part of the eye and stops irreversible damage like Phthisis bulbi, which is a condition where the eye shrinks and loses function.
If the infection has spread internally leading endophthalmitis (an inflammation of the internal parts of the eye), panophthalmitis (infection of all parts of the eye), scleritis (inflammation of the sclera, which is the white outer wall of the eye), or you have a choroidal or retinal detachment (parts of your eye layers have separated), the prognosis or outcome is generally uncertain. A timely performed TPK (therapeutic penetrating keratoplasty), another type of corneal transplant, can help to restore the normal structure of the eye, and clear up early corneal opacification (clouding of the cornea), and later on, you can have optical penetrating keratoplasty, another type of cornea transplant, for visual restoration.
Possible Complications When Diagnosed with Pythium Keratitis
Possible complications associated with eye disorders could include:
- Melting of the cornea
- Puncture of the cornea
- A type of corneal bulge called Descematocoele
- Clouding of the lens, known as cataract
- Inflammation inside the eye, known as Endophthalmitis
- Inflammation of the whole eye, known as Panophthalmitis
- Detachment of the layer of blood vessels at the back of the eye, referred to as Choroidal detachment
- Retinal detachment, often associated with sudden vision loss
- Scleritis, inflammation of the white part of the eye
- Total loss of vision, or blindness
- Shrunken and non-functional eye, known as Phthisis bulbi
Recovery from Pythium Keratitis
After undergoing a surgical procedure called TPK or Trabeculectomy, patients are initially provided with hourly rounds of two types of medicines: linezolid and azithromycin, which are applied topically. The intensity of these medicines would be gradually lessened based on the patient’s progress.
In addition to these, post surgery, other eye drops are employed – homatropine, to decrease eye pain caused by muscle spasms, timolol to prevent a condition called secondary glaucoma (a situation where fluid builds up in your eye, causing pressure and vision issues), and small doses of antibiotics like moxifloxacin and gatifloxacin to avoid bacterial infections. These antibiotics are used for at least 2 weeks following surgery.
If lab tests reveal the presence of a fungus called Pythium both before and after the surgery, health professionals can start administering steroids, which can help reduce inflammation, after 3 weeks of surgery. This happens only if they are confident that no Pythium fungus remains.
However, if the patient tests positive for Pythium before surgery but negative after, steroids can be started after a 2-week course of anti-Pythium drugs. These steroids, like prednisolone or dexamethasone, are initially applied 4 times a day for 2 months, then gradually lessened over 9 months based on the patient’s progress.
The essential process for recovery is consistent counseling after surgery and regular check-ups. Patients need to be aware that a procedure called optical penetrating keratoplasty may be required in the future once the eye is completely free from any infection.
Preventing Pythium Keratitis
Patients need to be educated on how to maintain cleanliness when handling and using contact lenses. Keeping the lenses clean helps prevent infections. Agricultural workers, in particular, are at risk of developing a type of eye infection called Pythium keratitis due to work-related injuries. If you happen to be an agricultural worker, it’s very important to use eye shields or goggles while working in the fields to protect your eyes.
Besides, patients should be informed about the importance of applying their prescribed medications regularly. It’s also imperative that patients understand the need for regular follow-up with their doctor, and in cases where the condition isn’t improving, a procedure known as keratoplasty (a type of corneal transplant) might be necessary.
