Category Archives: Chagas' Disease Primer

A Chagas’ Disease Primer: Part 6

Chronic Chagas’ Disease

This is where the problem is.
Most people won’t get signs of acute infection, so they won’t know that they are infected.
In 70% of cases, that’s fine. As far as we know, nothing will come of that.

But the other 30%, anywhere from 10 -30 years later, will go on to develop chronic Chagas’ Disease.

Let’s review. We have our  assassin bug,

Triatoma dimidiata, important vector in Mexico

which transmits the single-celled protozoan parasite, Trypanosoma cruzi (in its feces)

A T. cruzi parasite, among red blood cells on a slide

The bug poop gets rubbed into a mucous membrane (like the conjunctiva around the eye) or the bite made by the bug.
Let’s look at the life cycle again:

For those of you who care, the trypomastigote is the infective stage, that is the stage that can be passed from bug to mammal and mammal to bug. The amastigote is the stage that multiplies in tissue.

Don’t get hung up on the names. It’s just to see that different stages do different things–one goes around to infect different cells, the other works inside the cells.

Detail of above diagram

Trypomastigotes have flagella, whip-like structures that allow them to move around, amastigotes don’t. On a blood smear you can see the trypomastigotes squiggling around among the blood cells.

Amastigotes seem to like replicating in the cells of the heart’s muscle.

That is not a good thing.

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A Chagas’ Disease Primer: Part 5

If you wish to read the Chagas’ Disease primer in order, click here to go to Part 1 and follow the links.

Acute Chagas’ Disease? What are the chances?

If a person gets bit by an infected chirimacha or vinchuca (the Peruvian and Argentine words for the assassin bug, respectively, is it likely that acute illness will ensue? What percentage of persons bit will get the symptoms that the previous primer post elaborated?

Fortunately, very few will get sick, perhaps less than 5%.These people won’t get the flu-like illness, nor will they get the chagoma. Life will go on as if nothing had ever happened.

Which is good, right?  After all, current estimates (we’ll talk more about these estimates later)  put the number of those at risk for getting assassin bug bites at around 100 million.

As it turns out, it might be better to know that you’ve been bitten. While feeling kind of punk for a few weeks would really stink, it would be good to get some kind of sign that the little parasites were working their way through your system. As it turns out, acute Chagas’ Disease isn’t the problem. It’s the chronic form that shows up 20-30 years later, when it’s too late to do much about it.  30% of those infected will get the chronic form, which could be anywhere (once again, those wildly-ranging estimates) from 8 million to upwards of 12 million people in Latin America.

A Chagas Disease Primer: Part 4

If you wish to read the Chagas’ Disease primer in order, click here to go to Part 1 and follow the links.

Acute Chagas’ Disease

When a person gets infected with T. cruzi, what happens? (Quick review: the patient has been bitten by a kissing bug, also known as an assassin bug. The bug defecated on the person it was biting, and the patient scratched the bite, smearing the bug poop–filled with parasites–into the wound)

The parasites–in the infective trypomastigote stage (see the life cycle diagram from Part 3)–entered the patients blood stream and began to multiply, causing the acute form of Chagas’ disease.

Symptoms of acute Chagas’ Disease

Getting acute Chagas’ Disease is sort of like the flu. If you were unlucky enough to get infected, you might get a mild case, to the point where it’s inapparent. On the other hand, you might get pretty sick. However, even if you do get pretty sick, chances are that you’ll recover.

The flu-like symptoms are typical: Fever, headache, fatigue, body aches, vomiting, diarrhea.

One  symptom of note is the chagoma, a swelling that occurs at the bite site. This is  not an influenza-like symptom, and can often be an important aid in diagnosis, especially in pediatric cases where the patient still hasn’t learned to speak or may be unaware of the bite (assassin bugs are strictly noctrnal). A chagoma that occurs over the eye is called Romaña’s sign. Because victims are often bit in bed, the face is a common site for bites to occur (thus the name “kissing bug”). Bug feces are capable of infecting through the conjunctiva as well as through breaks in the skin.

Romaña's Sign

A Chagas’ Disease Primer: Part 3

If you wish to read the Chagas’ Disease primer in order, click here to go to Part 1 and follow the links.

Life Cycle of Trypanosoma cruzi
Below is the life cycle of T. cruzi.

Countless medical and veterinary students have been up late nights cursing life cycles, trying to remember the difference between Strongyloides stercoralis, Strongyles vulgaris, and Aelurostrongylus abstrusus . Parasitologists (at least male, heterosexual parasitologists), however, would rather look at complicated life cycles than pictures of Anita Ekberg in her prime.

The recommendation of this blog is to read this and get familiar with it. You don’t need to memorize it to understand Chagas’ disease. (Click on the diagram for a larger, more legible view.)

As far as life cycles go, it’s relatively uncomplicated. Write to us if you have any questions. Thanks to the CDC for the diagram.

A Chagas’ Disease Primer: Part 2

If you wish to read the Chagas’ Disease primer in order, click here to go to Part 1 and follow the links.

OK, where were we?

Chagas’ Disease is caused by the protozoan parasite Trypanosoma cruzi, and is spread by the bite of something called the kissing or assassin bug. We compared it to malaria, another protozoan, vector-borne disease.

But whereas most vector-borne diseases are spread via the saliva of the vector (the parasite malaria, the bacterium Lyme disease, the virus Yellow Fever), Chagas’ Disease is spread by feces of the assassin bug. The bug defecates while it eats, depositing its parasite-laden feces onto the host’s skin. When the host scratches the area, rubbing the feces  into the wound made by the bite, he (or she) becomes infected.

The Assassin Bug: Approximately 2 cm. of repugnant, disease-spreading ugliness

A Chagas’ Disease Primer: Part 1

As  Chagas’ Disease is rather unknown here in the Northern Latitudes, this blog has decided that it’s time to give our readers (assuming that we have any) a good background on this malady. It’s our goal to get Chagas’ Disease–with anywhere from 8 to 15 million persons infected–the attention that it deserves. 

What is Chagas’?
Chagas’ Disease is infection with the parasite Trypanosoma cruzi. T. cruzi is a protozoan parasite, meaning it’s a single-celled eukaryotic pathogen, as opposed to the worms (like tapeworms and roundworms) and insects (like fleas, lice and ticks ) that we normally think of. Think more of malaria  ( a protist that infects the liver and red blood cells) , amoebic dysentery, or cryptosporidiosis.

Like malaria (but unlike amoebic dysentery or cryptosporidiosis), Chagas’ Disease is a vector-borne disease. The vector in Chagas’ disease is a bug, commonly known as a kissing bug (because it often bites its sleeping victims on the face) or an assassin bug (the name we clearly prefer on this blog).

Parasitic diseases generally rank highest on the gross-out scale, above viruses, bacteria, and fungal infections.While the manifestation of clinical Chagas’ Disease isn’t as outwardly repulsive as, say, Guinea worm, its mode of transmission is. Stay tuned for Part II.