This parasite can generate a series of clinical symptoms, such as diarrhea or dysentery.
Even so, knowing the infectious dynamics of this parasitic microorganism is of great interest to anyone interested in the world of epidemiology. That is why here we tell you everything you need to know about balantidiasis and its causal agent.
Balantidiasis: an easily treated disease
As is common in any disease of parasitic origin, knowing the causal agent is the first key to being able to deal with it. For this reason, below we present you in a general way the protozoan Balantidium coli.
Characteristics of the parasite
Balantidium coli is the largest protozoan that parasitizes man. In addition, it is a general microorganism, as it is capable of infecting people, pigs, cows, camels, primates, horses and rodents. Like many other pathogens, it presents two forms in its life cycle:
- Cyst : state of rest and inactivity of the microorganism that allows it to endure in the environment.
- Trophozoite : activated vegetative form, which feeds, reproduces and moves thanks to its ciliated structures. It measures up to 155 micrometers.
Both forms are easily recognizable because they present a kidney-shaped macronucleus and a circular shape in the case of the cyst and pear-shaped in the case of the trophozoite.
A simple life cycle
Cysts are the forms responsible for balantidiasis. Normally, these microorganisms are ingested by man or other animals through infected food or water. From here, the cysts transform into mobile phases (trophozoites) and these settle in the large intestine.
Here, the trophozoites carry out their vital functions and reproduce by binary fission, an asexual process based on the division into two genetically equal copies of the first microorganism. Subsequently, encystment occurs again, preparing the parasite to exit with the host’s faeces. The trophozoites can also come out with the fecal material, surviving several days in the environment, to later give rise to the aforementioned encystment.
Possible hosts
One of the essential keys to understanding any epidemiological cycle is knowing perfectly the hosts that can transmit the disease. According to a large animal study in Bangladesh (103 samples), the carriers of balantidiasis are as follows:
- 54.7% of the contaminated fecal samples were from cows.
- 42% corresponded to pigs.
- More than 70% of the infected cows were adult.
- In the case of pigs, 65% of those infected were young.
Although the epidemiological bias by age and sex in farm animals is not yet completely clear, one thing can be elucidated: the main reservoirs are cows and pigs.
Naturally, humans become infected by handling the meat products of these mammals, or by coming into contact with water or surfaces contaminated with their faeces.
Clinical considerations of balantidiasis
Understanding any disease requires several steps. The first of these, as we have seen, is to describe the causal agent, its biological cycle and the possible sources of infection. These are attributes of the parasite itself, which is why we have focused on the biological features of the disease.
Now, how does this pathogen spread around the world? What symptoms does it cause and how serious are they? are there treatments? All these questions are medical considerations to take into account once the parasite has been described. Therefore, here are the answers.
1. Epidemiology (causes)
Balantidiasis is a disease with worldwide distribution, although its prevalence is low. Various studies report that it is more common in tropical and subtropical areas, especially when population centers are in close contact with their livestock. Worldwide, various studies estimate that the percentage of people affected is less than 0.1%.
Even so, there are areas that are more affected by the pathogen, especially when the health and hygiene conditions are not adequate. For example, in Latin America it is estimated that 1% of the population is infected, with certain foci where it can reach 2.3%.
To put into perspective the little clinical relevance of balantidiasis, a study in 1988 reported that, to date, only 1,000 cases had been detected in humans and 100 in monkeys. In any case, these numbers seem to underestimate the true prevalence of the disease, since diagnosing it in low-income areas is a complicated task. Among the areas most affected by the pathogen we find the Philippines, Mexico, South America and Papua New Guinea.
A different story is when we consider infectious episodes in non-human animals, such as pigs. This disease causes economic losses in livestock activities throughout the world, since it decreases the production of meat and promotes the slaughter of large groups of livestock when it is detected. In the case of pigs, for example, the prevalence (proportion of infected individuals) can be 80 to 100% in certain sources of infection.
It is not necessary to resort to theoretical frameworks to understand the number of pigs infected with balantidiasis in the world. For example, in Brazil it has been calculated that 60.9% of the pigs that live there are contaminated with Balantidium coli. In other geographic areas such as Iraq, a prevalence of almost 30% was observed in cows. All these percentages, although they are a bit dizzying, underline the presence of this pathogen in the animals of the agricultural industry .
2. Symptoms
The disease is usually asymptomatic and has a very good prognosis. Still, as is the case with all parasitic infections, immunocompromised people are at risk, as they may not be able to cope with the pathogen. There are three clinical manifestations of balantidiasis :
- Asymptomatic or with very mild diarrhea , the most frequent.
- Severe dysentery, bloody diarrhea in prolonged infections. Rare.
- Chronic infection with abdominal pain, nausea, vomiting, and weight loss.
All these clinical manifestations are produced by the mechanical action of the movement of the trophozoites, as well as by their hyalunoridase activity, which produce ulcerative lesions in the colon tissue.
According to the Centers for Disease Control and Prevention (CDC), extraintestinal infection of the parasite is rare, but not impossible. Pathologies such as peritonitis or liver abscesses can occur if Balantidium coli manages to perforate the intestine. This is the most serious representation of balantidiasis.
3. Diagnosis
As we have said before, this parasite is the largest protozoan capable of infecting humans. Due to the considerable size (within the micrometric scale, of course) of both the trophozoites and the cysts, a microscopic coprological analysis is sufficient to diagnose the disease. To do this, fecal samples are obtained from the patient and the infective forms of the parasite are sought in them.
4. Treatment
The recommended treatments to combat balantidiasis are tetracycline, metronidazole or iodoquinol.
In the case of metronidazole, various studies have investigated its efficacy and interaction with the parasite . In one of them, after ingestion of 5 grams over 5 days or 12.5 grams spread over 10 days in adults, the infection remitted in all patients on the fourth day of treatment. All subsequent fecal samples appeared negative (no sign of the parasite) and no negative effects of its administration were described.
These results underscore the ease and efficacy of drugs in addressing the disease.
Conclusions
Balantidiasis is a disease with very little incidence in humans, but of course it is close to us if we look at cattle. As in almost all parasitic cycles, unsanitary conditions and the proximity of population centers to livestock activities are perfect breeding grounds for the transmission of the disease.
Also, not all probability of infection is reduced to being in contact with the feces of infected animals. Due to the resistance of both the cyst and the trophozoite, an act as simple as that of a pig defecating in an unpurified water hole can infect an entire community.
That is why it is essential, within possible limits, to maintain hygienic conditions, food analysis procedures and maximum health to avoid outbreaks of balantidiasis within the population.
Bibliographic references
- Mata, C.S., & Chaves, H.M. (2011). Balantidiasis presentation of a clinical case. Medical Journal of the University of Costa Rica, 5(1), 58-62.
- Hernandez, F., & Rivera, P. (1992). Balantidiasis: compilation of concepts. Costa Rican Journal of Medical Sciences, 13(1-2), 67-75.
- Balantidiasis, CDC. Retrieved July 13 at https://www.cdc.gov/dpdx/balantidiasis/index.html
- Woody, N. C., & Woody, H. B. (1960). Balantidiasis in infancy: Review of the literature and report of a case. The Journal of Pediatrics, 56(4), 485-489.
- Paul, T. R., Begum, N., Shahiduzzaman, M., Hossain, M. S., Labony, S. S., & Dey, A. R. (2019). Balantidiasis, a zoonotic protozoan infection, in cattle and domestic pigs. Bangladesh Journal of Veterinary Medicine (BJVM), 17(1), 31-37.
- Garcia-Laverde, A., & De Bonilla, L. (1975). Clinical trials with metronidazole in human balantidiasis. The American Journal of Tropical Medicine and Hygiene, 24(5), 781-783.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.
