Black fungus or mucormycosis is a very rare infection seen in humans. Under normal circumstances our immune system is able to beat such infections with ease. But with the present Covid infections, many of the patients end up with a very weak immune system, which is perfect environment for the black fungus to attack.
Many of us might be surprised with the kind of diseases that have popped up in the last two years. As Darwin proposed will it be the survival of the fittest, Is the nature challenging us , proving us its existence or is it fighting back ? Which one is true? Well, only time shall tell. we may have progressed in science, but we have to keep in mind we still have no remedy for common cold.
Viruses are still a major threat to mankind.
However, it is the Black fungus that is causing the most problem recently.
What is Black Fungus?
Black fungus or mucormycosis is a infection caused by exposure to mucor molds that are found in soil, manure, decaying matter. They belong to the order Mucorales and are the normal residents of our environment. Humans may inhale these mucor spores on a regular basis, but as normally humans have a well designed defense mechanism these spores are destroyed before they cause any serious problems.
But on the other hand a person suffering from a diseases or a condition that has critically impaired his/ her immune system is at a very high risk of getting a black fungus infection. Therefore, a person who has had a Covid infection may have a rather weak immune system making them the perfect host for black fungus or mucormycosis.
MUCORMYCOSIS / BLACK FUNGUS
Most species of this family may not be able to infect humans or animals due to their lack of ability to survive in warm environment. But the thermotolerant mucor fungus , that infect humans not only do they spread rapidly but also induce necrotizing infections known as mucormycosis or zygomycosis.
- Kingdom: Fungi
- Division: Zygomycota
- Class: Mucormycotina
- Order: Mucorales
- Family: Mucoraceae
- Genus: Mucor
TYPES OF REPRODUCTIONS
- Vegetative reproduction
- Sexual reproduction
- Asexual reproduction
- It consists of mother mycelium.
- Each fragments can split into many sub- units.
- Each sub-units have a capability to grow like new mycelium.
- Like fragmentation methods.
During sexual reproduction, compatible strains form short, specialized hyphae fuse, a thick-walled, spherical zygosporangium develops. The zygosporangium containing a single zygospore which the undergoes nuclear karyogamy and meiosis (sexual recombination). They then germinate to form hyphae or a sporangium.
When erect hyphal sporangiophores are formed. The tip of the sporangiophore swells to form a globose sporangium that contains uninucleate, haploid sporangiospores. An extension of the sporangiophore called the columella protrudes into the sporangium which then rupture and release spores. These spores then germinate readily to form a new mycelium on appropriate substrates.
Although mucormycosis is an opportunistic pathogen, it has an mortality rate higher than 40%. With the recent reports being higher in COVID associated patients, one should take care. The other risk factors include patients with diabetes mellitus, burns, iron overload, transplantation, chemotherapy, intravenous drug use.
There are five major clinical forms of mucormycosis
- Rhinocerebral mucormycosis
Commonly seen in patients with diabetes, organ transplant receipients, renal transplants. The patients suffers from facial swelling , nasal discharge , necrotic black lesions on the hard palate, black pus from the eyes, sinus pain, fever etc.
- Pulmonary mucormycosis
Inhalaing the mucor spore may lead to there spread in the pulmonary tissues, which leads to angioinvasion and ultimately tissue necrosis. Difficulty breathing , fever , cough, chest pain are some of the other symtoms.
- Cutaneous mucormycosis
Affecting the skin, these are normallay seen in patients who are immunosupressed and suferring from burns or had any locla skin trauma. It may start with acute inflammation with pus, swelling, necrosis, red lesions and if not treated may progess from to ulcers with black eschars.
- Gastrointestinal mucormycosis
It is usually seen in severely malnourishes patients who have ingested the funhal spores. Stomach, colon, ileum may al be affected by the infection. The symptoms include nausea, vomiting, abdominal pain, gastrointestinal bleeding and necrosis etc.
- Disseminated mucormycosis
These may follow any type of mucormycosis above described but the mist common sites are brain, heart, spleen, other organs may also be affected.
PATHOGENESIS OF MUCORMYCOSIS
Mucormycosis is characterized by angioinvasion that result in vessel thrombosis and ultimately tissue necrosis. Necrosis contribute to prevent the delivery of leukocytes or antifungal agents to the site of infection.
So how does this actually happen?
Black fungus or Mucorales produce fungal toxins that inhibit protein synthesis and lead to tissue destruction. According to recent research analysis done on Mucorales. It has been stated that these fungal toxin resemble a ricin ( secondary metabolites in plants) , therefore the toxin has also been named as ‘mucoricin’. So, the infection is initiated when the fungal spores are inhaled. In the absence of phagocytosis ( as in immunocompromised patients) the fungal spore bind to the nasal epithelial cells or to the alveolar epithelial cells to induce invasion.
The spores germinate and progress ultimately leading to the production of mucoricin (fungal toxin). Mucoricin then bind to the tissue cells , inhibits protein synthesis which leads to apoptosis and necrosis. As the toxin also affects vascular permeability it is often associated with tissue edema too.
Although during the tissue damage our immune system recognizes the infected area and produces an inflammatory immune response recruiting neutrophils, phagocytes etc. to the site, it does only little damage to the invading fungus. Both the dead and live black fungal hyphae are capable of releasing the toxin mucoricin, resulting in more host cell damage. The necrotic tissue is best place for the fungus to proliferate protected from drugs and lymphocytes. Fungi being saprophytes feed on the necrotic tissue and propagate.
Patients suffering from diabetes are also at a high risk of mucormycosis, due to the elevated levels of iron in the blood (ketoacidosis). Usually, iron in our body is always found in a bound state (with proteins such as transferrin). Diabetic ketoacidosis stimulates an acidotic condition decreasing their iron binding capacity.
Iron is an essential element for cell growth and development . Therefore, the fungal species utilize different mechanisms to extract them from the host. Free iron in the serum is a positive environment for the propagation of fungus.