Babesiosis is normally an infection of cattle, causing a condition called red water fever (probably because it causes the cattle to pee blood and have a fever!). It is therefore yet another zoonotic infection in humans.
Babesiosis is an infection caused by the parasite Babesia spp. There are a number of different subspecies that cause disease depending on where you are in the World. In Europe (France, Ireland, Finland, Sweden, Norway, Poland, Croatia, Spain and Portugal) it is caused by B. divergens whereas in the USA (New England, New York, New Jersey, Minnesota also and Wisconsin) it is mainly caused by B. microti. Other subspecies include B. duncani and B. venatorum. Studies from the USA have shown evidence of past infection in up to 16% of people in high incidence areas.
Babesiosis is transmitted by infected ticks; Ixodes ricinus in Europe and Ixodes scapularis in the USA. It is usually the juvenile nymph tick that bites, often in the spring and summer. There have also been cases of transmission by blood transfusion (200 cases), organ transplantation (2 cases) and also congenitally (11 cases) though these cause are still thankfully uncommon.
Babesiosis is fairly common in the USA with over 2,000 cases per year but fortunately it is rarely acquired in Europe, only 37 recorded cases. Up until recently there had only been 11 “imported” cases in the UK, well until July this year when someone acquired the infection here in North Devon! Apparently there have been cases of red water fever in cattle in North Cornwall as well. Okay, that’s a couple more potential stay-cation destinations crossed off my list for this year!!
How does Babesiosis present?
The incubation period for babesiosis is 1-4 weeks, although when transmitted by blood transfusion it can be 1-6 months. Babesiosis is asymptomatic in 20% of adults and 40% of children. Most infections are mild-to-moderate but severe life-threatening infections can occur.
- Mild-to-moderate (<4% parasitaemia) - fever, flu-like illness
- Severe (>4% parasitaemia) - jaundice, haemolytic anaemia, renal failure, acute respiratory distress syndrome (ARDS), cardiovascular instability, liver failure, disseminated intravascular coagulation, coma and death
Severe infections usually only occur in patients with underlying immunodeficiency such as splenectomy, organ transplantation, chemotherapy, HIV infection, immunomodulation (with etanercept, infliximab, rituximab) and also in neonates.
The mortality is 3-9% of all those unwell enough to be admitted to hospital, 20% if they are also immunodeficient and 37% if they develop ARDS as part of their illness.
Chronic infection for over 1 year with babesiosis is common, even in asymptomatic people. However if these “chronic carriers” are immunosuppressed in some way e.g. chemotherapy, splenectomy, HIV infection, then they can become symptomatic and develop severe disease without any “recent risk factors” for tick bites… sneaky huh!?
How is Babesiosis diagnosed?
The parasites cause a parasitaemia (they are in the blood stream) where they enter red blood cells; this is identical to malaria which also enters red blood cells.
Also like malaria the diagnosis is usually made by seeing trophozoites (parasites) in the red blood cells on a thin blood smear. This is technically difficult though and requires an experienced microscopist (this is the kind of thing you need a senior haematology BMS or Consultant haematologist for). A blood smear also allows an estimation of the number of red blood cells affected which helps to predict the risk of severe disease (again the same as malaria).
Another way of diagnosing babesiosis is using PCR on blood, but this is a reference laboratory test. The PCR can stay positive for 1-2 years after treatment in some people; presumably fragments of parasite DNA hang around in various parts of the blood stream making the test positive. It does mean that PCR is not a good way of detecting relapsed or reacquired infections.
It is important to consider co-infection with other tick borne diseases e.g. Lyme disease (4-13% of cases) as many tick-borne diseases are transmitted by the same types of ticks.
How is babesiosis treated?
Asymptomatic babesiosis doesn’t need treating… which is good as the patient and the “average doctor” probably won’t know or think about it!
Mild-to-moderate infection is usually treated with PO Azithromycin PLUS PO Atovaquone but usually does not require hospitalisation.
Severe infection is usually treated with IV Clindamycin PLUS PO Quinine, as an inpatient. Severe infection will also require supportive care e.g. renal replacement therapy, mechanical ventilation, cardiovascular support etc. The normal duration of treatment is 7-10 days.
So as if we didn’t have enough to worry about with all of those weird infections returning travellers bring back from exotic holidays we now have to be aware that those same weird infections are “appearing” in the UK… marvellous! Maybe I’ll just hide under my duvet for my holiday this year… it just seems a bit safer…. [BUT!!! You said we could clear out the garage!] Maybe North Devon does sound better after all.