Case 110 – summary

Thankyou for all your help this week

This week we had a look at 4 films where there were visible organisms.

Film 1 – babesia

Film 2 – malaria – p.vivax

Film 3 – malaria – p.falciprum

Film 4 – diplococci – neisseria meningitidis

When looking at films where there is a suspicion on infection clinical details are very important. This will enable the appropriate tests and blood film preparations to be made to aid diagnosis. Travel history is very important to aid diagnosis.

Film 1 – babesia.

Babeosis is a tick borne protozoan infection that is see in Europe, Asia and north west and north eastern america. Humans are usually affected by babesia microti. Many patients will have no, or only mild symptoms. Symptoms can include fever, headache, myalgia and nausea/vomiting. In patients who are asplenic or immunocompromised severe disease may occur.

Symptoms are usually related to the parasitaemia of red cells by babesia. Infected red cells can contain more than one merozoite. The ring forms may be mistaken morphologically for p.falciprum malaria so travel history is very important when looking at individual cases.

Haemolytic anaemia and haemoglobinuria can be present in severe infections. Some patients may also develop ARDS and/or multi organ failure.

Although the majority of cases are transmitted via bites from infected ticks. Transmission has also been seen from blood transfusions from infected donors. Perinatal and transplacental infection can also occur.

Symptoms can persist for several months after initial infection, and can also recur, particularly in asplenic patients and those on immunosuppressive treatment.

In patients with lower parasitaemia multiple thin films or stained buffy coat preperations may be needed to identify the parasite. Wright or giemsa stained thin films can show the ring forms. In some cases the ‘maltese cross’ made up of merozoites. P.falciprum can be mistaken for babesia, Maltese crosses are not seen in p.falciprum, there is also a lack of hemozoin in babesia.

Serological testing and PCR to investigate for babesia can be performed.

Patients with babeosis will need treatment with antibiotics and may need HDU/ITU care in severe cases. All suspected cases should be discussed with local infectious disease/microbiology team. In severe cases exchange transfusion may be considered.

Case 2 – p.vivax malaria

Case 3 – p.falciprum malaria

Travel history is again very important when malaria is suspected. Not only when trying to establish the likely parasite, but also establish the likelihood of drug resistance.

P.vivax is the most common human malaria transmitted globally, although p.falciprum has a higher mortality.

Patients may present with fever, myalgia, headache, nausea/vomiting, and can present with symptoms of haemolysis and organ failure in more severe cases. Occasionally patients can present with features of cerebral malaria including seizures and altered consciousness.

When examining blood films identification of parasites can be made on thin films, however it is important to look at think films as low levels of parasites may be missed on thin films. Thick films should be stained with giemsa or field stain, and thin films with giemsa or leishman stain. A thick film should be examined for around 10 minutes, which equates to around 200 oil immersion fields before it is declared negative. Each thick film should be reviewed by 2 people.in p.falciprum and p.knowelsi the percentage of cells with parasites should be calculated and reported as this may effect the choice of treatment. If there is doubt as to whether parasites can be seen on the thick film, the entire thin film should be reviewed.

Rapid diagnostic tests(RDT) can be used when suspecting malaria, but are not a substitute for microscopy.

Quantification of parasites should be done daily until no parasites are seen

Patients who have traveled to the Asia-Pacific area who are thought to have p.malariae should have samples sent urgently to the malaria reference lab for pcr as p.malariae and p.knowlesi are very difficult to distinguish from one another.

Samples should be sent to a malaria reference lab if there are positive results, if there is discrepancy between films and

RDT or if there is strong clinical suspicion after discussion with ID team but no positive results. If films are negative then team should consider repeating the film in 12-24 hours, and then again at 24 hours.

PCR is more sensitive than microscopy for malarial parasites however is not widely available, but is used in the reference lab, and can be particularly useful in patients with mixed infection.

All labs involved in testing for malarial parasites should be involved in EQA schemes for parasites.

When diagnosing p.vivax, it is important to consider testing for g6pd deficiency as treatment may involve primaquine which can precipitate haemolysis in patients with g6pd deficiency.

As p.vivax can lie dormant in liver cysts recurrent infections can occur.

The treatment of p.falciprum is guided by the severity of the disease. Severe infection can be rapidly fatal so prompt treatment can be life saving.

In severe cases of malaria red cell exchange can be considered.

Links at the bottom show some aids to diagnosing malaria from the CDC. There is also a link to the bsh guidelines for malaria diagnosis.

Film 4 – diplococci – neisseria meningitidis

In this case a patient was admitted collapsed and unwell with no collateral history and they were subsequently diagnosed with neisseria meningitidis bacteraemia and suspected meningitis.

The blood film demonstrates diplococci. It is unusual to see bacteria on blood films and when this is seen it should rapidly be reported to the caring physician to enable appropriate treatment as these patients are usually extremely unwell. If the patient has no signs or symptoms of infection then contamination can be considered.

Thankyou for all your help this week. This week we looked at 4 cases where microscopy was important in the diagnosis of infections.

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Bsh guideline on laboratory diagnosis of malaria

https://onlinelibrary.wiley.com/doi/full/10.1111/bjh.12572

CDC information on malaria

https://www.cdc.gov/dpdx/malaria/index.html

CDC bench aid to p.vivax diagnosis

https://www.cdc.gov/dpdx/resources/pdf/benchAids/malaria/Pvivax_benchaidV2.pdf

CDC bench aid to p.falciprum diagnosis

https://www.cdc.gov/dpdx/resources/pdf/benchAids/malaria/Pfalciparum_benchaidV2.pdf

CDC bench aid to p.ovale diagnosis

https://www.cdc.gov/dpdx/resources/pdf/benchAids/malaria/Povale_benchaidV2.pdf

CDC bench aid to p.malariae diagnosis

https://www.cdc.gov/dpdx/resources/pdf/benchAids/malaria/Pmalariae_benchaidV2.pdf

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