I’ve been lucky enough to head to Peru twice. A while after the second trip, I decided to be a blood donor for the first time. It cropped up that I’d been to Peru and the lady suddenly looked worried.
Lady: “Hang on, I just need to go and get my colleague.”
Both come back: “When were you there, how long for, did you sleep under any thatched roofs….?”
Now to anyone not interested in parasites or working in healthcare, this might seem like an odd question. But what these folks were really asking me was:
“Have you been bitten by this?”
Image from wikipedia
“…and infected by this?”
Image from CDC
Chagas disease is a disease spread by the Triatomine bug (aka “Kissing Bug”) and is also known as American Trypanosomiasis. If you’ve ever heard of Sleeping Sickness in Africa, this parasite, Trypanosoma cruzi is closely related to the parasite that causes that disease. These bugs feed on everything and live in thatched roofs, cracks and crevices. So as you can imagine, poorer rural folk, often with limited healthcare, are sadly predominantly affected. I have it in my notes that 50% of bugs are infective.
I couldn’t remember why they were called Kissing bugs but a quick google confirmed a nightmare (which makes sense when I tell you the signs and symptoms in a minute)- it’s because the bug bites humans around the eyes and mouth…while you sleep…
Honestly, these bugs are plain rude and the most ‘UN-BRITISH’ bugs ever.
They have a bad habit of pooing on your skin as they feed from your blood, leaving you to scratch the poo into your own bite accidentally! And incidentally, scratching in T cruzi. I should add that they don’t need to bite you. Those lovely juice drinks you might have had in rural South America? They may well have ground up bug or bug poo in it and oral transmission is BAD (yes, I drank them too). Furthermore, as might be inferred from the conversation I had at the Blood Donation centre, transmission via infected blood products is also possible.
More About the Parasite
But whilst I might be a little light-hearted about the method of transmission, about the disease itself I most definitely am not. The WHO estimates that 6-7 million people are affected by Chagas disease (WHO 2017). Most of these are in South America but there is Chagas in Spain.
T. cruzi has a complex life cycle split into two stages- those that occur in the bug, and those in the human. They multiply in the midgut of the bug to form the infective form in the picture above- metacyclic trypomastigotes. Knowing the life cycles of parasites can help us to decide treatment strategies.
If anyone is particularly interested in learning parasitology, I always think of T cruzi‘s trypomastigotes as being more ‘C’ shaped than T brucei (African form)- C for cruzi.
Image from CDC
Signs, Symptoms and Diagnosis
Patients may be symptomless in the chronic form but there is usually an acute phase within 3 weeks of the bite, where the patient may feel like they have a viral illness- they might get a fever, go off their food, get a bit of lymph node swelling. Some notice the bite site itself- a firm small swelling, sometimes discoloured, called a chagoma. Others yet may present with Romana’s sign- painless swelling of the eyelids and associated conjunctivitis caused by the parasite entering through the eye.
The problem is the chronic form. For ages, years even, the parasite can ‘hide’ where it multiplies, often within ‘smooth’ muscle- namely usually the gut. Worst still though, it can affect the nervous system and also the heart, where it can cause: ‘heart blocks’ (where the normal electrical rhythm of the heart, the one that times your heart beat, gets disturbed); deformities of the heart; heart failure, and even sudden death.
Diagnosis is based on lab tests of the blood (Giemsa stains, serology, PCR, buffy coat analysis, culture…) but my FAVOURITE way it is diagnosed is by xenodiagnosis- we give it back to the bug- HA!
Because chronic disease carriers can be tricky to diagnose, some doctors use ‘clean’ lab grown Kissing Bugs and get them to bite the patient. We then examine the gut of the bug later to see if the parasite is there- clever isn’t it?
There are two treatments for Chagas- benznidazole (which from what I’ve read and learnt, seems better tolerated and is oral) and nifurtimox. They can be almost 100% effective in the early stages of the disease (WHO 2017) but if caught later, or during the chronic phase, they are not nearly as good. This is to the point that my notes suggest that treatment in chronic cases might be pointless as the risk from the drugs is higher than their benefit. Furthermore they can’t be used to treat pregnant women. Note that there are cases of reactivation of infection and these respond fairly well, occurring typically in patients with immunosuppression (HIV+, cancer…). There’s a lot of work though that is based on getting rid of the Kissing Bug itself (“vector control”).
I had the good fortune to see someone from the Drugs for Neglected Diseases initiative (DNDi) give a lecture the other day. This fabulous organisation, funded by charitable donations, works to make drugs for Neglected Tropical Diseases (NTDs) and neglected populations. Within this category are children. Developing drugs for children is tricky: drugs are processed differently by their growing bodies; trying any research on children is always understandably a trickier ethical approval process and, frankly, if children don’t like something they won’t have it. DNDi has developed an oral formulation of benznidazole specially for kids and continues to work finding other treatment options for other NTDs too.
The problem with treating NTDs isn’t solely ‘heartless’ Big Pharma. I’m not one to generally defend massive drug companies but I try to be a realist and I try to be fair. Their help is essential in creating and distributing many of the drugs that DNDi are developing, and many of them now have charitable arms working for good causes in Africa… The problem with NTDs is that they are often tricky organisms to treat and that where they occur is often fraught with issues. Lower Income Countries are often constrained by infrastructure (drug procurement and distribution issues, adequate staffing, poor monitoring and evaluation, patient follow up is difficult…) and anything intravenous is reliant on extra equipment, trained staff, additional time and infection control issues. Obviously, the drugs also need to be cheap. Therefore oral is often preferable. DNDi have their work cut out for them for a lot of NTDs but interesting work it certainly is.
If you’re interesting in supporting their work, please visit the ‘donate’ part of their webpage.
Oh, and if you’ve not had a Kissing Bug bite- please give blood.
If you have, please seek help.
Mostly my own notes from my DTM&H course
World Health Organisation: http://www.who.int/mediacentre/factsheets/fs340/en/
Centre for Disease Control and Prevention: http://www.cdc.gov/parasites/chagas/index.html
Thanks to Wikipedia too for some of the CC pictures