The Biomedical Scientist walked hesitantly into the duty Microbiologists office.
“We have a mould growing in a blood culture” they said.
“You mean a yeast?” asked the Microbiologist.
“Nope, definitely a mould” replied the BMS.
“A contaminant maybe?” asked the Microbiologist again, now starting to hope this was the case.
“Nope, definitely not a contaminant” replied the BMS.
“Please tell me this was handled in Cat 3?” asked the Microbiologist again, starting to sound worried and thinking he should maybe put the Health and Safety Executive (HSE) telephone number into his phone!
“Nope, not in Cat 3” replied the BMS looking crest fallen, “but it should have been… I think it’s Talaromyces marneffei”
The Microbiologist just stared at them lost for words… why did it always happen when he was on duty?!
What is Talaromyces marneffei?
T. marneffei is a dimorphic fungus; it has two types of growth depending on the temperature (a bit like cheese! Cheese is a solid block when in the fridge but when sliced and put on toast under a grill it’s all gooey!!!) It used to be called Penicillium marneffei, but like many other microorganisms it has undergone a recent name change just to keep us on our toes.
“We have a mould growing in a blood culture” they said.
“You mean a yeast?” asked the Microbiologist.
“Nope, definitely a mould” replied the BMS.
“A contaminant maybe?” asked the Microbiologist again, now starting to hope this was the case.
“Nope, definitely not a contaminant” replied the BMS.
“Please tell me this was handled in Cat 3?” asked the Microbiologist again, starting to sound worried and thinking he should maybe put the Health and Safety Executive (HSE) telephone number into his phone!
“Nope, not in Cat 3” replied the BMS looking crest fallen, “but it should have been… I think it’s Talaromyces marneffei”
The Microbiologist just stared at them lost for words… why did it always happen when he was on duty?!
What is Talaromyces marneffei?
T. marneffei is a dimorphic fungus; it has two types of growth depending on the temperature (a bit like cheese! Cheese is a solid block when in the fridge but when sliced and put on toast under a grill it’s all gooey!!!) It used to be called Penicillium marneffei, but like many other microorganisms it has undergone a recent name change just to keep us on our toes.
In the human body, and therefore in blood and tissue samples, and on agar at 37oC T. marneffei grows like a yeast. However, at environmental temperatures of 25-30oC the growth changes and T. marneffei starts to grow as a mould with “fluffy” colonies.
Where does Talaromyces marneffei come from?
T. marneffei is found endemically in South East Asia (Thailand, Vietnam, and Cambodia) as well as Northern India, Southern China, Hong Kong, Taiwan and Malaysia. Only humans and bamboo rats are known to be hosts for this fungus however the exact environmental reservoir isn’t known… so we can’t just blame the rats!
The assumption is that T. marneffei is a soil organism as the number of cases increase during wet periods and are highest in those who have exposure to soil, however no one has as yet grown the fungus reliably from soil. It could also be that those particular warm, wet conditions favour a species e.g. the rats again, and so there is an association with the condition without there being a direct causal route.
Infection with T. marneffei has only been described in people who live in or have travelled to endemic countries.
How does infection with T. marneffei present?
T. marneffei is an opportunistic pathogen; it requires a defect in the host immune system to cause infection. The most common immunodeficiency linked to infection with T. marneffei is Human Immunodeficiency Virus (HIV) infection, in particular when the CD4 count is <100 cells/microL. Between 1991 and 2004 there were >6000 cases in Thailand associated with HIV.
The main route of acquisition is thought to be through inhalation of spores, although a case of localised infection did occur after a needlestick injury in a lab.
Infection with T. marneffei, known as talaromycosis, should be suspected in any HIV positive patient from an endemic country. It should also be suspected in anyone who has travelled to an endemic country who has become immunosuppressed. Presentations are split into mild, moderate and severe:
More specific symptoms by body system, in addition to fever, include:
It is also possible to become a chronic carrier of T. marneffei. A study from Thailand showed that 10% of the population tested had evidence of latent infection with the fungus; they had essentially become carriers. More worrying is that a patient from Australia developed infection when suddenly immunosuppressed, 10 years after travel related exposure. This means that there is the potential for anyone who has been to an endemic area to develop infection later in life if they are immunosuppressed… and that includes me as I have been to Northern Thailand and Hong Kong… It also shows that increasingly, with worldwide travel so commonplace, a travel history is now very relevant and so important!
How is talaromycosis diagnosed?
Talaromycosis is diagnosed by culturing the fungus from blood, skin, bone marrow or lymphoid tissue. The key to the diagnosis is to recognise that growing moulds from blood, bone marrow and lymphoid tissue is very rare; in reality the only moulds to grow in these samples are dimorphic fungi and Fusarium spp. so alarm bells should ring when this happens. On the other hand, fungal infections of skin are common and so there is more danger of missing the diagnosis if a skin sample is the only sample available.
T. marneffei is a Biological Safety Level 3 microorganism and all samples should be handled in a Level 3 Biological Safety facility.
A provisional diagnosis can be made based on the Gram film appearance of the yeast with oval or elongated shaped buds with a clear central septum. Further identification is then made after demonstrating that the fungus grows as a yeast at 37oC and a fluffy mould at 25-30oC. The fluffy mould is green on the surface and red underneath due to a red pigment; the pigment also diffuses out into the clear agar. Apparently MALDI-ToF can identify the yeast and mould forms but note, an extraction step prior to MALDI-ToF is required.
Where does Talaromyces marneffei come from?
T. marneffei is found endemically in South East Asia (Thailand, Vietnam, and Cambodia) as well as Northern India, Southern China, Hong Kong, Taiwan and Malaysia. Only humans and bamboo rats are known to be hosts for this fungus however the exact environmental reservoir isn’t known… so we can’t just blame the rats!
The assumption is that T. marneffei is a soil organism as the number of cases increase during wet periods and are highest in those who have exposure to soil, however no one has as yet grown the fungus reliably from soil. It could also be that those particular warm, wet conditions favour a species e.g. the rats again, and so there is an association with the condition without there being a direct causal route.
Infection with T. marneffei has only been described in people who live in or have travelled to endemic countries.
How does infection with T. marneffei present?
T. marneffei is an opportunistic pathogen; it requires a defect in the host immune system to cause infection. The most common immunodeficiency linked to infection with T. marneffei is Human Immunodeficiency Virus (HIV) infection, in particular when the CD4 count is <100 cells/microL. Between 1991 and 2004 there were >6000 cases in Thailand associated with HIV.
The main route of acquisition is thought to be through inhalation of spores, although a case of localised infection did occur after a needlestick injury in a lab.
Infection with T. marneffei, known as talaromycosis, should be suspected in any HIV positive patient from an endemic country. It should also be suspected in anyone who has travelled to an endemic country who has become immunosuppressed. Presentations are split into mild, moderate and severe:
- Mild (skin lesions only)
- Moderate (multi-organ involvement but with stable respiratory and cardiovascular function)
- Severe (multi-organ involvement with respiratory and cardiovascular failure)
More specific symptoms by body system, in addition to fever, include:
- Reticuloendothelial system - widespread lymphadenopathy, splenomegaly and hepatomegaly
- Respiratory - cough, shortness of breath and chest pain, diffuse infiltrates on chest x-ray
- Gastrointestinal – diarrhoea and abdominal pain
- Skin - papules on face, chest and extremities in 70% of patients; papules become necrotic and collapse in the centre
- Mucosa – similar appearance to skin lesions occurring in mouth, oropharynx, stomach, colon and genitalia
- Neurological – altered mental state, confusion, decreased consciousness
- Musculoskeletal - occasionally septic arthritis or osteomyelitis
It is also possible to become a chronic carrier of T. marneffei. A study from Thailand showed that 10% of the population tested had evidence of latent infection with the fungus; they had essentially become carriers. More worrying is that a patient from Australia developed infection when suddenly immunosuppressed, 10 years after travel related exposure. This means that there is the potential for anyone who has been to an endemic area to develop infection later in life if they are immunosuppressed… and that includes me as I have been to Northern Thailand and Hong Kong… It also shows that increasingly, with worldwide travel so commonplace, a travel history is now very relevant and so important!
How is talaromycosis diagnosed?
Talaromycosis is diagnosed by culturing the fungus from blood, skin, bone marrow or lymphoid tissue. The key to the diagnosis is to recognise that growing moulds from blood, bone marrow and lymphoid tissue is very rare; in reality the only moulds to grow in these samples are dimorphic fungi and Fusarium spp. so alarm bells should ring when this happens. On the other hand, fungal infections of skin are common and so there is more danger of missing the diagnosis if a skin sample is the only sample available.
T. marneffei is a Biological Safety Level 3 microorganism and all samples should be handled in a Level 3 Biological Safety facility.
A provisional diagnosis can be made based on the Gram film appearance of the yeast with oval or elongated shaped buds with a clear central septum. Further identification is then made after demonstrating that the fungus grows as a yeast at 37oC and a fluffy mould at 25-30oC. The fluffy mould is green on the surface and red underneath due to a red pigment; the pigment also diffuses out into the clear agar. Apparently MALDI-ToF can identify the yeast and mould forms but note, an extraction step prior to MALDI-ToF is required.
Click for larger image
You might also discover talaromycosis inadvertently when investigating a fungal infection; a positive galactomannan (a fungal antigen), often detected in the blood of patients with invasive aspergillosis, can also be found in talaromycosis although the galactomannan levels are lower than in aspergillosis.
How is talaromycosis treated?
The mortality for untreated or delayed treatment of moderate or severe talaromycosis is 97%; so rapid treatment is required.
Treatment is divided into induction and maintenance phases. Treatment should continue until the patient’s immune system has recovered; if this has occurred before the maintenance phase then the treatment can be stopped after induction.
How is talaromycosis treated?
The mortality for untreated or delayed treatment of moderate or severe talaromycosis is 97%; so rapid treatment is required.
Treatment is divided into induction and maintenance phases. Treatment should continue until the patient’s immune system has recovered; if this has occurred before the maintenance phase then the treatment can be stopped after induction.
Click for larger image
Laboratory exposure
As T. marneffei is classified as a Biological Safety Class 3 microorganism samples from a suspected patient should be processed in Containment Level 3 in the same way as other Class 3 organisms like Brucella spp.. Having said this, the risk of laboratory acquisition of T. marneffei is much lower than for other high risk microorganisms. However the risk occurs with handling the mould form (25-30oC); there is no risk in handling the yeast form (37oC). You still need to process this in Cat 3 though as if it is left out on the bench it will start to grow the risky mould form!
In fact to date there are only two reported cases of talaromycosis laboratory acquisition; one was the needlestick injury mentioned above and the other was a Doctor with HIV who developed talaromycosis (despite no travel to an endemic country) after walking through a laboratory where the fungus was being handled on an open bench! It was actually this laboratory acquired case in the 1990s that lead to the introduction of Biological Safety Level 3 rather than Level 2 to process specimens.
If a laboratory exposure does occur then the incident should be managed in the same way as previously discussed for brucellosis. This involves identifying at risk staff, notifying the Trust, Public Health England and the Health and Safety Executive through RIDDOR. The main difference from brucellosis is in the prophylaxis offered to staff members handling the mould form; talaromycosis prophylaxis is PO Itraconazole 200mg BD for 6 weeks (with their levels being checked after a week).
So the Microbiologist immediately checked to make sure the patient was on IV Liposomal Amphotericin B which they were. The fungus was confirmed as Talaromyces marneffei and a number of staff were identified as having been exposed. The staff members were started on PO Itraconazole. The Trust, PHE and HSE were all told and an investigation started to see if there were any lessons which could be learnt to stop this happening again… one option the Trust Risk Office thought of was “to stop a particular Microbiologist being on duty as he always seemed to “find” trouble…
As T. marneffei is classified as a Biological Safety Class 3 microorganism samples from a suspected patient should be processed in Containment Level 3 in the same way as other Class 3 organisms like Brucella spp.. Having said this, the risk of laboratory acquisition of T. marneffei is much lower than for other high risk microorganisms. However the risk occurs with handling the mould form (25-30oC); there is no risk in handling the yeast form (37oC). You still need to process this in Cat 3 though as if it is left out on the bench it will start to grow the risky mould form!
In fact to date there are only two reported cases of talaromycosis laboratory acquisition; one was the needlestick injury mentioned above and the other was a Doctor with HIV who developed talaromycosis (despite no travel to an endemic country) after walking through a laboratory where the fungus was being handled on an open bench! It was actually this laboratory acquired case in the 1990s that lead to the introduction of Biological Safety Level 3 rather than Level 2 to process specimens.
If a laboratory exposure does occur then the incident should be managed in the same way as previously discussed for brucellosis. This involves identifying at risk staff, notifying the Trust, Public Health England and the Health and Safety Executive through RIDDOR. The main difference from brucellosis is in the prophylaxis offered to staff members handling the mould form; talaromycosis prophylaxis is PO Itraconazole 200mg BD for 6 weeks (with their levels being checked after a week).
So the Microbiologist immediately checked to make sure the patient was on IV Liposomal Amphotericin B which they were. The fungus was confirmed as Talaromyces marneffei and a number of staff were identified as having been exposed. The staff members were started on PO Itraconazole. The Trust, PHE and HSE were all told and an investigation started to see if there were any lessons which could be learnt to stop this happening again… one option the Trust Risk Office thought of was “to stop a particular Microbiologist being on duty as he always seemed to “find” trouble…
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