Casoni Test for Hydatid Disease

No one likes parasites, especially doctors! Treating parasitic infections can be tedious and stressful. Complicated treatment regimens, constant follow-ups, poor patient compliance, and surgery in severe cases make the entire process tiring. Early detection and diagnoses are of utmost importance for effective treatment. Here’s some information about the Casoni test – one of the first diagnostic tools for echinococcus infections. 

What is the Casoni Test?

The Casoni Test is an intradermal hypersensitivity test that has been widely used as a diagnostic tool for hydatid disease. This test was created by Tomaso Casoni, an Italian physician. He was the first doctor to outline a test for immediate allergic reactions to hydatid fluid injected into the skin. 

Aim of the Casoni Test

To detect the presence of Echinococcus granulosus parasite infection in the human body. Thus providing a diagnostic confirmation for hydatid disease.

This test was specifically designed for cystic echinococcosis, but before diving deep into the details of the test, let us familiarize ourselves with hydatid disease and why a diagnostic tool was needed. 

What is Hydatid disease?

Hydatid disease or cystic echinococcosis is a parasitic disease caused due to an infection by the larva of Echinococcus granulosus. This condition involves the growth of cysts on various organs of the body like- liver, lungs, bones, kidneys, and spleen.

How is it transmitted?

For those who do not know, hydatid disease is a zoonotic disease – meaning that this disease can be transmitted from animals to humans. E. granulosus that causes these cystic infections in humans are majorly found in domesticated animals such as dogs, sheep, goats, swine, cattle, camels, and yak. Furthermore, this infection can also spread through accidental ingestion of parasitic eggs in contaminated food and water

Why was a test needed?

Hydatid disease is a silent killer. These cysts caused by the infection grow unnoticed and spread in the liver, lungs, and other organs of the body. The incubation period of the disease produced no symptoms. It was only when the cysts grew and spread that the clinical signs of hydatidosis manifested. The signs and symptoms of this infection include:

  • Abdominal pain, nausea, vomiting (seen usually when the cysts grow in the liver)
  • Chest pain, chronic cough, and shortness of breath (seen usually when hydatids grow in the lungs)
  • Other signs include anorexia, weight loss, and weakness

Most people visit the doctors when they suffer from such symptoms but by that time it’s too late. Early and appropriate diagnosis of this infection is vital to ensure proper treatment. 

Enter – Casoni Test

Although now obsolete, the Casoni test was a major breakthrough in the detection of parasitic infection. As mentioned earlier, this test was first described by Tomaso Casoni, at a time when hydatid disease hit its peak in Europe, Africa, the Middle East, and other parts of the world. 

Let’s understand the principle

The Casoni test is a hypersensitivity test. It involves the injection of hydatid fluid into the skin. This fluid is obtained from cysts present in bovine animals. It is then made ready for use by sterilization using the Seitz filtration method. Upon injection, wheals with outrunners, edema, and erythema are observed. These wheals indicate the presence of hydatid disease in an individual. These reactions are observed due to interactions with hydatid antigens present in the bovine cyst.

What will you need?

  1. Safety equipment: Masks and gloves
  2. Instruments: Syringes, cotton 
  3. Chemicals:
    1. Rubbing alcohol/ spirit
    2. Hydatid fluid
    3. Control fluid (Normal Saline can be used for this test)

How to perform this test?

  1. Start by ensuring your own safety. Wear a mask and a pair of gloves before starting the procedure.
  2. The outer part of the upper arm is used for this procedure.
  3.  In case this procedure has been performed before, use a fresh patch of skin so as to avoid false results.
  4. Sterilize the part of the skin that you are using for the test with rubbing alcohol.
  5. Fill up the syringe with Hydatid fluid.
  6. Around 0.25 mL or 4 minims of hydatid fluid will be required for performing this test.
  7. This fluid is injected intradermally to raise a white area approximately one centimeter in diameter.
  8. Inject the same quantity of saline solution into the skin a few centimeters away from the site of the hydatid fluid injection.
  9. Other control procedures involve the use of the stroke test. 

The stroke test involves rubbing the skin of the forearm firmly with a blunt instrument. The outer portion of the other arm may also be used for this. 

How to measure the reactions

After injecting the patient with the hydatid fluid, wheal formation is seen with pseudopodial runners and erythema. This reaction is seen within 30 minutes of the injection. The greatest diameter of the wheal is measured. Since the wheal is irregular in shape, two or more diameters can be taken for better size measurement. 

What’s positive and what’s not!

Upon administration of hydatid fluid, there are chances that the patient may show an immediate reaction or a delayed reaction. The parameters for a positive result differ for both these conditions. Here is what reaction you should consider as an indication for hydatid disease.

  • For immediate reaction on administration
    Reactions are considered as positive when the wheal:
    • Measures at least 2.4 cm in one diameter
    • Measures at least 2.2 cm in two diameters
  • For delayed reactions on administration
    Delayed reactions usually last up to 24 hours. Positive reaction for the test is recorded between eighteen and twenty-four hrs after injection. Here’s what is considered as an indication for cystic echinococcosis
    • Redness and edema that is at least 4 cms in diameter in the vicinity of the site of injection

Precautions to be taken

  1. Learn about the medical history of the patient:
    Conditions like pruritus, urticaria, hay fever, and asthma may produce false results.
  2. Find out if the individual has taken this test before. Chances of repeated skin insult are higher in such people.
  3. Be prepared for an anaphylactic shock. An adrenaline injection does the trick in curing the symptoms.
  4. Keep on the watch for delayed reactions.

Limitations to this test

Considering the fact that the Casoni test came way back in the 1900s, comparing it to modern-day techniques and tests would be unfair. Nevertheless, here are some limitations of this test that have been overcome in this day and age. 

  1. Since this is a hypersensitivity-based test, the reactions are uncomfortable and can be irritable for the patients.
  2. Prone to a lot of false-positive results.
  3. Limited Sensitivity: A study showed that the Casoni test showed positive results in:
    1. 74% of hydatid disease patients
    2. 82% of patients with liver cysts
    3. 67% of patients with lung cysts
  4. Patients are prone to allergic reactions or anaphylactic shocks

Alternatives to the Casoni Test

With the advent of technology and sophisticated imaging techniques, numerous safe and efficacious alternatives to the Casoni test have emerged. Here are some tests used to detect echinococcus diseases in this day and age.

  1. Imaging technology
    1. Ultrasonography
    2. Magnetic Resonance Imaging (MRI)
    3. Computed tomography scan (CT Scan)

All these imaging techniques are used to complement each other for proper diagnosis.

  1. Serological Tests:
    1. Indirect hemagglutination assay test (IHA Test)
    2. Enzyme linked immunosorbent assay (ELISA Test)
    3. Immunoelectrophoresis Test (IEP Test)

All these tests detect the presence of anti-Echinococcus antibodies (Immunoglobulins)

We hope that this article has outlined the important role that the Casoni test played in the diagnosis of Echinococcus diseases. Furthermore, we also aspire that this blog has outlined the importance of timely and precise diagnosis of cystic echinococcosis and the plethora of diagnostic tools that are available to do so.

References

  1. Echinococcosis. Available from: https://www.who.int/news-room/fact-sheets/detail/echinococcosis Accessed on: 13th January 2022
  2. Beshyah SA. Tomaso Casoni (1880-1933): A Pioneer Remembered. Libyan Journal of Medicine. 2008;3(4):1-5.
  3. Lass N. The Casoni test in Echinococcus disease.  International Congress for Allergy. 1st International Congress, Zürich 1951. Basel, Karger, 1952, pp 618-621
  4. Casoni Test. A review. Available from: https://pmj.bmj.com/content/postgradmedj/22/249/203.full.pdf Accessed on: 13th January 2022
  5. Krige JE, Beckingham IJ. Liver abscesses and hydatid disease. Bmj. 2001 Mar 3;322(7285):537-40.

FAQs

What is the Casoni Test?

The Casoni Test is an intradermal hypersensitivity test that has been widely used as a diagnostic tool for hydatid disease.

What is Hydatid disease?

Hydatid disease or cystic echinococcosis is a parasitic disease caused due to an infection by the larva of Echinococcus granulosus.

How is it transmitted?

Hydatid disease is a zoonotic disease – meaning that this disease can be transmitted from animals to humans.

Why was a test needed?

Hydatid disease is a silent killer. These cysts caused by the infection grow unnoticed and spread in the liver, lungs, and other organs of the body. The incubation period of the disease produced no symptoms. It was only when the cysts grew and spread that the clinical signs of hydatidosis manifested.

How to perform this test?

1. Start by ensuring your own safety. Wear a mask and a pair of gloves before starting the procedure.
2. The outer part of the upper arm is used for this procedure.
3. In case this procedure has been performed before, use a fresh patch of skin so as to avoid false results.
4. Sterilize the part of the skin that you are using for the test with rubbing alcohol.
5. Fill up the syringe with Hydatid fluid.
6. Around 0.25 mL or 4 minims of hydatid fluid will be required for performing this test.
7. This fluid is injected intradermally to raise a white area approximately one centimeter in diameter.
8. Inject the same quantity of saline solution into the skin a few centimeters away from the site of the hydatid fluid injection.
9. Other control procedures involve the use of the stroke test. 

How to measure the reactions?

After injecting the patient with the hydatid fluid, wheal formation is seen with pseudopodial runners and erythema. This reaction is seen within 30 minutes of the injection. The greatest diameter of the wheal is measured. Since the wheal is irregular in shape, two or more diameters can be taken for better size measurement. 

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