The killer kissing bugs and Chagas Disease.

Think back to the last time you were bitten by a mosquito. Did the bite itch? If so, did you scratch it? The body’s instinctive reaction to an itch is to scratch, so it’s highly likely you did give in to the temptation. In the case of our humble mosquito bite, scratching may exasperate and prolong the irritation or even lead to secondary infection. If you think these are serious complications of a little relief via scratching, perhaps we should compare it to the potential consequences of scratching a triatomine bug bite.

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The triatomine bug (Source: CDC)

Triatomine bugs- also known as “kissing bugs” or “assassin bugs”- are large bloodsucking insects that occur mainly in Latin America and Southern USA (WHO, 2017). They can be found in low socioeconomic domestic environments in areas such as under porches, in poorly constructed walls or roofs, between rocky structures, under cement, or in chicken coops, and are all potential vectors of the Chagas Disease parasite- Trypanosoma cruzi. The kissing bugs hide during the day and become active at night when they feed on human blood, typically taking advantage of an exposed area of skin such as the face. The parasite is then deposited when the bugs defecate near the bite. Instinctive scratching or rubbing can smear bug faeces or urine into the bite, eyes, mouth, nose, or any other break in skin, permitting T. cruzi to access the bloodstream unbeknownst to the host. Other modes of transmission account for just 20% of transmissions (Aiga, 2012) and include consumption of food contaminated with T. cruzi, blood transfusion or organ transplantation from infected donors, and passage from an infected mother to her newborn.

 

Shortly after inoculation, a high number of parasites circulate in the blood stream, with the acute phase commencing. Symptoms are present in less than 50% of cases (WHO, 2017) and may include:

  • Fever
  • Fatigue
  • Body aches
  • Diarrhea
  • Nausea
  • Vomiting
  • Hepatosplenomegaly
  • Swelling at the site of inoculation (notably the eye which is known as Romaña’s sign)

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Romaña’s sign (Source: CDC)

These are most severe in individuals with a compromised immune system (CDC, 2010). Although these symptoms often resolve spontaneously, even with treatment, the disease will progress to the chronic phase. Most patients will be unaware of their infection during this phase, however 30-40% of cases will develop complications, the most frequent and severe (being potentially fatal) of which is chronic cardiomyopathy (RAGCP, 2014). Other patients suffer from digestive complications (typically enlargement of the oesophagus or colon), neurological, or mixed alterations.

 

Global estimates for the number of people infected with T. cruzi range from 8 million to 12 million, whereas the estimates for the number of annual deaths attributable to Chagas Diseases are less variable ranging from 10, 600 to 12, 500(Stanaway, 2015). As a low-mortality high-morbidity disease, much like many of the other NTDs, the majority of the global health burden stems from the health care requirements, non-fatal health loss and chronic disability. Chagas is estimated to be responsible for 550, 000 disability adjusted life years (DALYs), precipitating an economic burden of USD $7.19 billion per year. This places the economic burden of Chagas well in excess of other prominent diseases in all socio-economic populations such as rotavirus ($2.0 billion), cervical cancer ($4.7 billion) and Lyme disease ($2.5 billion) (Stanaway, 2015).

 

With no vaccination available for Chagas Disease, vector control is currently the most effective method of prevention. Bearing this in mind, it is surprising that we don’t invest more in this intervention. In Colombia alone, the economic burden of medical care for Chagas Disease (not factoring in loss of productivity) was estimated to be USD $267 million in 2008. Only USD $5 million was allocated to vector control via insecticides (WHO, 2017). This amounts to less than 2% of the funds allocated to medical care, despite triatomine bugs accounting for 80% of all transmissions of T. cruzi. We must advocate the cost effective nature of vector control prevention and make better use of the resources we have. From both a humanitarian and economical perspective, prevention is superior to treatment. This becomes even more evident when we consider the current treatments for Chagas are unsatisfactory. The drugs of choice Benznidazole and Nifurtimox are not cost effective and produce an elaborate concoction of side effects. Additionally, they are of no use in patients who have already developed heart damage (Ross, 2017).

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An example of the impoverished environment triatomine bugs thrive in (Source: Stanford University)

The elimination of Chagas Disease is fundamental in breaking poverty cycles. The kissing bugs invade dilapidated, poorly constructed houses and their impoverished inhabitants. Subsequent poor access to health and decreased productivity entrap these people in the poverty cycle and it continues to gain momentum. There is an urgent need for more research and development. A greater emphasis must be put on vector control and developing a vaccination. More effort must be dedicated to screening and etiological treatment. If a humanitarian perspective isn’t enough to motivate many of us to act, as it seems has been the case with many Neglected Tropical Diseases for numerous years, perhaps the fact that some scientists have predicted that Chagas may become more common in developed areas, as we increase infrastructure in areas where triatomine bugs are found, or that they could spread North to the USA with climate change would hit a bit closer to home and force us to act (Ross, 2017). Either way, we must kill the killer kissing bugs.

BY JEMMA SAXTON
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