Since the first reported evidence of oral transmission in 1965, outbreaks of oral Chagas disease have gained importance as an emerging route of transmission. In some regions, it is considered to be the transmission mode in up to 50% of cases in certain geographical locations like in the Amazon basin ^[1][40]. Due to the severity of the disease, many who become infected via oral ingestion will manifest significant signs and symptoms of acute CD, which can lead to fulminant myocarditis and heart failure, meningoencephalitis, and even life-threatening shock from parasitemia ^{[1][2][3][4][5][6][7][8]}[11,12,13,14,17,18,40,41].

The incubation period following the oral ingestion of T. cruzi-contaminated products is approximately 3–22 days, in contrast to 4–15 days for vectorial transmission and 8–160 days for transfusion- and transplant-related transmission ^[9][1]. A shorter incubation period is likely due to the overall significantly increased parasite load compared to the other routes of transmission. Symptoms and rapid disease progression in those who are immunocompetent are not common among other forms of transmission like vectorial, congenital, or transfusion-related transmission ^[10][4]. The vast majority of those with acute oral Chagas have fever (71–100%), but other systemic symptoms are notable and include facial edema, lower extremity edema, myalgia, generalized lymphadenopathy, abdominal discomfort, dyspnea, vomiting, diarrhea, hepatomegaly, splenomegaly, headache, chest pain, cutaneous erythematous rash, jaundice, arthralgia, epistaxis, hematemesis, melena, and palpitations ^{[1][2][3][4][5][6][7][8]}[11,12,13,14,17,18,40,41]. Facial edema, typically involving the entire face and portions of the lips, is present in 57–100% of those with acute oral CD ^[1][10][4,40]. This can be differentiated from vectorial transmission, where we more commonly see unilateral periorbital swelling (a.k.a. Romaña’s sign) in those with acute symptoms ^[1][10][4,40]. The robust systemic immune response that is seen in those with acute oral CD is suggested to occur due to a more efficient transmission after penetration through the oral, pharyngeal, and gastric mucosa. In addition, we also see many-fold higher parasitic loads present in contaminated food and drink products as compared to vectorial transmission, and thus exacerbated clinical signs and symptoms of infection. It has been estimated that a single crushed triatomine harboring T. cruzi can contain 600,000 metacyclic trypomastigotes as compared to 3000 to 4000 per microliter of infected triatomine fecal material ^[10][4].

The largest outbreak of orally transmitted Chagas was linked to contaminated guava juice consumption in a Venezuelan elementary school located in Caracas ^[4][13]. The outbreak reported a total of 119 confirmed and suspected cases of CD. Clinical courses of those confirmed or suspected cases reported 75% were symptomatic and 20.3% required hospitalization. One five-year-old child died of acute myocarditis ^[4][13]. These percentages differ from those reported in vectorial transmitted Chagas, reported to be asymptomatic for the acute phase of infection in up to 95–99% of cases ^[9][1]. Cardiac abnormalities are seen more frequently after oral transmission of T. cruzi as opposed to vectorial transmission ^{[1][8][11][12]}[40,41,42,43]. Of these, electrocardiographic abnormalities are reported in a majority of patients, specifically ventricular polarization disturbances and pericardical involvement in young soldiers in Colombia ^[1][11][40,42]. Electrocardiographic abnormalities in oral Chagas, as described in the largest reported outbreak (N = 103), were present in 66% of confirmed cases and are reported with a predominance in children under 18 years old compared to adults (69.7% vs. 56%) who were infected ^[11][42]. The more frequently observed electrocardiogram (ECG) alterations include ST segment and T wave abnormalities (37%) as well as QT prolongation (2.9%) ^[11][42]. The right bundle branch block, which is common in chronic Chagas heart disease (5–25% of chronic Chagas heart disease), was also seen in acute oral CD but with a much lower frequency at 1.94% (N = 2/103), and the left bundle branch block was seen at 2.9% (N = 3/103) ^[11][42]. ST segment and T wave abnormalities were seen between both age groups and were more common in <18 years (72% versus 19%) as opposed to adults ^[11][42]. Echocardiograms in the mentioned study were performed if the ECG was abnormal (66%; N = 68/103). This revealed 32% (N = 22) with mild to moderate pericardial effusion seen on echocardiogram as well as 33% (N = 33/103) with arrhythmias. This includes 22% (N = 23/103) supraventricular arrhythmias, ventricular arrhythmias 5.8% (N = 6/103), and atrioventricular block 2.9% (N = 3/102) ^[11][42]. Ventricular dysfunction with low ejection fraction has also been described in 27% of cases of oral CD ^[8][41].

Trypanosoma cruzi is a generalist parasite that can infect >136 triatomine vector species, essentially any mammal, and almost all mammalian tissues ^[13][14][44,45]. A flagellate kinetoplast, this parasite’s life cycle involves three distinct forms, with the trypomastigote and amastigote forms of clinical relevance. The traditional T. cruzi pathogenesis follows the route of trypomastigote systemic circulation, adherence to smooth muscle tissue, conversion to the amastigote form, intracellular amastigote reproduction and nest expansion, eventual cellular damage yielding parasite egress, and the cycle repeats with newly formed trypomastigotes systemically circulating ^[15][46]. T. cruzi demonstrates tropism for cardiac and gastrointestinal smooth muscle tissues, although the parasite can be found disseminated throughout the human body ^[14][16][45,47]. Intracellular parasite growth produces a pronounced inflammatory infiltrate response, with cellular damage presenting as inflammatory lesions and fibrosis ^[15][46]. The inflammatory infiltrate can directly destroy neurons and cardiac fibers, in contrast to the physical fibrotic damage caused by necrotic amastigote nest hollows ^[16][47].

This cycle slows down and becomes subclinical during the intermediate phase, which lasts indefinitely without chemotherapeutics. In approximately 30% of patients, this cellular damage cycle cryptically continues at an accelerated pace until advanced disease clinically manifests. The factors that contribute to pathogenesis and reactivation are largely unknown but are hypothesized to correlate with parasite discrete typing unit ^[17][18][19][48,49,50], high-fat diets ^[20][21][51,52], co-infections ^[22][23][53,54], and host immunogenetics ^[24][55]. Murine models indicate three potential pathogenic pathways collectively, independently, or in verse contribute to cellular damage: autoimmune, neurogenic, or pro-inflammatory damage mediated by certain cytokines such as interleukin (IL)-6 and IL-17 ^{[15][25][26][27][28][29][30][31]}[3,46,56,57,58,59,60,61]. While evidence supports all three pathways, the strongest contemporary evidence supports a hybrid pathogenic mechanism of host autoimmune activation and persisting parasitic material that stimulates inflammatory host response ^[30][60].

Most people who have been infected with the parasite are thought to have acquired T. cruzi via the vector-borne route. This involves an infected triatomine defecating fecal material containing metacyclic trypomastigotes on an individual while being bitten. The parasite can then enter the body through the mucosa or a breach in the skin at or near the bite site. The rest of those who acquire the infection may do so via oral consumption, pregnancy, or other avenues. Given the recent emergence and rarity of oral T. cruzi transmission, the pathophysiology scientific literature is limited. Case reports verify that this mechanism is associated with greater disease manifestations and high mortality, suggesting an alternative acute disease pathogenesis process occurs. More research is needed to better understand this neglected route of T. cruzi infection.

Oral CD in Colombia has been associated with the possible consumption of contaminated fruit juices and food. In other mammalian hosts, the oral way is the most important transmission form ^[32][62]. In humans, it is debated which are the main sources of oral infection, from contaminated food through triatomine feces or directly macerated triatomines in beverages and fruit juices ^[25][3]. These contaminated food sources combine specific aliments that are more likely to be contaminated by insects or insect feces; however, any food or drink left unattended could potentially become contaminated from possible animal scent gland secretions ^[5][33][14,63]. Most of the time, the source of these oral transmissions is not described; however, there are two beverages in Colombia that have been associated with oral CD: palm wine and tangerine juice ^[25][34][35][3,26,27]. In 1999, during an outbreak in Guamal (Magdalena) municipality, 18 cases were found associated with palm wine (“vino de palma”), a fermented drink common in some Colombian regions ^[36][20]. This drink is prepared by performing a deep cut in the palm to reach the heart to obtain the sap, collecting several liters that are left to ferment. Sometimes, this drink is consumed immediately, and it could be infected by triatomine feces, which could then transmit the parasite orally. An outbreak in 2008 was associated with tangerine juice and was described as a source of orally acquired CD in Santander. It affected nine individuals who visited the same farm, and all had the same juice for breakfast ^[37][38][21,23]. The possible source was thought to be orange juice contaminated with insect feces contaminating the oranges which made the juice, or infected triatomines macerated within the sugar cane, that would have been posteriorly mixed with the juice and infecting the individuals consuming that juice ^[4][39][13,64]. Since orange juice is not macerated but squeezed, it is not clear how the juice becomes contaminated, and thus, the speculation on sugar cane contamination. A case series published in 2022 described two pediatric cases of acute oral Chagas disease, supposedly related to the consumption of sugar cane juice, also called “guarapo de caña” in Spanish ^[6][17]. Similarly, animal studies demonstrate sugar cane juice can remain infective for up to twenty-four hours post-inoculation ^[39][64].

Açai juice is a common source of orally acquired Chagas disease in Brazil, although Colombians have some national açai fruit farms and regularly import this juice from Brazil. It is thought the infected triatomines or triatomine feces-contaminated fruits are macerated with the fruits, thus contaminating the drink ^[32][62]. In an experimental study, they observed the parasite to survive between 24 and 72 h in several drinks, including mandarin, guayaba, and guanabana, and up to 384 h in guanabana when preserved at 4 °C; results were reproduced in a separate study with similar conditions for açai juice ^[40][41][65,66]. Further, some populations culturally use açai juice as a way to wean infants off breastmilk, and infants have developed Chagas cardiomyopathy following consumption of contaminated açai juice ^[42][67]. Considering juices are usually consumed within a short amount of time after preparation, it is important to note how 24 h would make this transmission route feasible and the most likely. No other juices and foods have been directly documented to be the source of infection in Colombia, but other ways of contamination of food and beverages can happen and should be considered.

When considering CD as food-borne, we need to look at the parasite’s life cycle. In the T. cruzi life cycle, the trypomastigotes in the blood will turn into an amastigote inside the muscle cells of the infected animals and humans ^[43][68]. It is discussed whether the infected muscle cells can be a source of infection in humans when eating infected mammalian meat. It has been demonstrated experimentally that opossums (Didelphis albiventris) can become infected by feeding on mice infected with T. cruzi, thus bringing attention to the possibility of oral transmission in humans through consumption of undercooked or raw infected meat ^[32][62]. In 2016, Sangensis et al. performed a systematic review evaluating the transmission of T. cruzi through the consumption of game meat, such as the nine-banded armadillo (Dasypus novemcinctus) ^[44][69]. The transmission through infected meat is considered rare, though possible, and at the same time has brought some controversies on whether there might have been infection through manipulation of the animal carcass during the butchering of the animal and the cooking process that led to cross-contamination and later infection ^[45][70]. In Colombia, the consumption of possibly infected wild animals such as armadillo (Dasypus species), opossum (Didelphis species), and lowland paca (Cuniculus paca) is common, regardless of being reservoirs for zoonotic diseases, and the butchering process is usually performed under unhygienic conditions that could potentially expose those manipulating animals and causing cross-contamination of the instruments used for cooking ^{[46][47][48][49]}[24,71,72,73]. Although there is a lack of evidence of transmission of T. cruzi from infected mammalian meat to humans, lowland paca (also known as “lapa”, “guagua” o “guartinaja”) has been associated with T. cruzi infection vectored by P. geniculatus. This bush meat is one of the most appreciated meats in the country, thus, infection through this route should be considered and evaluated ^[50][74]. Subsistence hunters among indigenous and rural communities within the southern Colombian Amazon, including the departments of Amazonas, Putumayo, Caquetá, Guainía, Guaviare, Vaupés, and other sections of Cauca, Meta, and Vichada, likely consume other known T. cruzi infected mammals, including the Nasua nasua or South American coati, the “kinkajou” (Potas flavus) and non-human primates ^[51][52][75,76]. Risks for consuming un- or undercooked T. cruzi-infected mammalian bush meat are not well understood among this population and could be considered a source of oral ingestion of the parasite.

In addition to the “traditional” food-borne transmission route by manipulating contaminated carcasses and contaminated food sources, some traditional cultural practices relate to the oral T. cruzi transmission. An example of those in Colombia and other Latin American countries is the use of armadillo blood (D. novemcinctus) and other body parts for their believed medicinal properties ^[47][53][71,77]. Nine-banded armadillos, called “gurre” in the Andean region of Colombia, are well-distributed wildlife in Colombia, and these are insectivorous mammals and can become T. cruzi reservoirs from ingestion of triatomine bugs, potentially becoming a source of infection ^[5][14]. Besides being used as a meat source, armadillos are captured and used for their supposed medical properties: the tail and shell are turned into a powder to relieve adverse effects of pregnancies, its fat is used to cure inflammation and ear pain, or varicose veins, and the blood is drunk to relieve asthma symptoms and other respiratory conditions ^{[54][55][56][57]}[78,79,80,81]. This cultural practice can bring undesired infections, especially the consumption of infected blood and undercooked meat ^[58][59][82,83]. In 2019, in Chocó, San José del Palmar, two family members were diagnosed with T. cruzi infection within a short period of time after both cases had allegedly consumed armadillo blood and, thus, obtained the infection from the consumption of such blood ^[60][31]. As a traditional cultural practice, it is important to consider this infection route to develop targeted interventions that are culturally sensitive to prevent additional cases.

Oral CD transmission is most recognizable when a cluster of acute CD cases is seen, presenting with clinical manifestations which is less likely to be seen in vector-borne transmission ^[10][4]. Accidental bug ingestion has been considered a possibility of oral transmission, which can occur if a triatomine becomes macerated within the food or beverages being prepared ^{[10][46][55][56]}[4,24,79,80]. The possibility of infection through ingestion of the bug relies on the triatomine parasite load, which can vary between species and the timing of previous infectious blood meal ^[61][62][63][84,85,86]. Although it is difficult to assemble evidence of an orally acquired infection after ingesting an infected triatomine insect, it is a plausible route of oral T. cruzi infection in humans. Some other forms of ingestion have been discussed in the literature. It has been considered that acutely infected mothers who were breastfeeding could potentially transmit the parasite orally from their breast milk ^[64][87]. Trypomastigotes have been found in the breast milk of several mothers that were in the acute and chronic phase through direct examination of the parasite; however, only one has been seen positive using xenodiagnoses, suggesting it to be unlikely to transmit the infection orally ^[65][66][67][88,89,90]. Some authors suggest that breast milk is a poor mechanism of transmission and that breast milk could potentially become cross-contaminated in mothers who have bleeding nipples and not from the milk itself ^[65][88]. Although it seems unlikely, in experimental settings, successful transmission of T. cruzi using unpasteurized human milk has been observed in mice ^[68][91]. However, no clinical evidence supports oral transmission naturally through breast milk, and further research should be conducted to consider this source of oral transmission. Water contamination has been mentioned as a source of T. cruzi infection ^[32][46][24,62]. Referencing an outbreak in Brazil, where the source of infection was suggested to be inadequately stored soft drinks and/or water ^[69][92]. The authors did not confirm water as the source of infection; thus, the suggestion has been considered not plausible, from experimental studies where the parasite does not show survival in water, eliminating the possibility of water being a source of infection ^[40][70][65,93]. Given the lack of evidence supporting water as the source of infection, it is likely that it is not a good transmission mechanism, and epidemiological studies should probably not consider it as the source of infection.

4. Opossums and Odoriferous Gland T. cruzi-Infected Secretions

The significance of Didelphis species as an indicator of environmental disruption and its role as a primary reservoir of T. cruzi in human-impacted ecosystems has been described in Colombia and other regions of continental Latin America ^[71][72][73][104,105,106]. Didelphis marsupialis is a synanthropic mesomammal that plays an important dual role in both sylvatic and peridomestic T. cruzi transmission cycles. Domestic transmission is also postulated, and D. marsupialis has been found infected with T. cruzi near populated metropolitan regions ^[74][107]. Multiple studies have shown that Didelphis species harbor T. cruzi and infectious trypomastigotes ^[75][76][77][108,109,110]. In Colombia, T. cruzi DTU TcI has been detected from anal gland fluid collected among trapped opossums in regions where active vector-borne and oral outbreaks have been described, most notably in the eastern plains and Caribbean regions ^[5][77](Figure 5) [14,110]. Employing molecular tools such as next-generation sequencing (NGS) of T. cruzi isolates collected from humans and D. marsupialis in Colombia have demonstrated genetic similarities that point toward anal gland secretions as a source of human infection ^[78][111]. A recently described investigation of a suspected oral outbreak of CD in Cubara, Boyacá, Colombia, found a possible epidemiological linkage between humans and D. marsupialis. Among the five index human cases, all had T. cruzi DTU TcI detected in the blood, and subsequently, the same was found among the five D. marsupialis captured near the human dwelling. Only one triatomine (P. geniculatus) was found, and it was negative for T. cruzi ^[79][35]. The epidemiological importance of Didelphis species as a potential zoonotic source of oral transmission via anal gland secretions needs rigorous investigation. However, evidence suggests this is likely another potential source of oral transmission of T. cruzi to susceptible hosts, such as humans and companion animals.