The Thai liver fluke causes quite a bit of human misery. This parasite infects fish living in the rivers of Southeast Asia, which, in turn, infects people who eat the fish.

Raw and fermented fish make up a big part of the diet of people in Southeast Asia. For example, in Thailand, a popular culinary item is called sour fish. This “delicacy” is prepared by mixing raw fish with garlic, salt, seasoning, and rice. After rolling the mixture into a ball, it is placed in a plastic bag and left to ferment in the hot sun for several days.

The fermentation process isn’t sufficient to kill the cysts of the Thai liver fluke embedded in the muscles of the infected fish. So, when people eat sour fish (or raw fish), they risk ingesting the parasite.

The Thai Liver Fluke Life Cycle

After ingestion, the cysts open in the digestive track of the human host, releasing the fluke. This parasite travels through the bile duct, making its way into the liver, where it takes up residence.

Once in the liver, the fluke lays eggs that are carried into the host’s digestive track by bile secreted by the liver. In turn, the eggs are released into the environment with human excrement. After being ingested by snails, the eggs hatch, producing larvae that escape from the snail. The free-living larvae infect fish, forming cysts in their skin, fins, and muscle.

Image: Life cycle of Opisthorchis viverrini. Image source: Wikipedia

The Thai liver fluke is a master of disguise, evading the immune system of the human host and living for decades in the liver. Unless the infestation is extreme, people infected with the fluke are completely unaware that they harbor this parasite.

Estimates indicate that 10% of the Thai population is infected with the Thai liver fluke. But in the villages of northern Thailand, where the consumption of raw and fermented fish is higher than in other areas of the country, 45% of the people carry the parasite.

The Thai Liver Fluke and Cancer

The Thai liver fluke can live for several decades in the host’s liver without much consequence. But eventually, the burden of the infection catches up with the human host, leading to an aggressive and deadly form of liver cancer that claims about 26,000 Thai lives each year. Once the cancer is detected, most patients die within a year.

Biomedical researchers think the liver cancer is triggered by the Thai liver fluke, which munches on the host’s liver. Interestingly, the fluke’s saliva contains a protein (called granulin-like protein) that stimulates cell growth and division. These processes help the liver to repair itself after being damaged by the fluke. In effect, the parasite eats part of the liver, supercharges the liver to repair itself, and then eats the new tissue, repeating the cycle for decades. The repeated wounding and repairing of the liver tissue accompanied by rapid cell division eventually leads to the onset of cancer.

The Thai Liver Fluke and God’s Goodness

The problems caused by the Thai liver fluke are not limited to the biomedical arena. This parasite causes theological issues, as well. Why would a good God create the Thai liver fluke? Questions like this one fall under the problem of evil.

Philosophers and theologians recognize two kinds of evil: moral and natural. Moral evil stems from human action (or inaction in some cases). Natural evil proceeds from nature itself—earthquakes, tornadoes, floods, diseases, and the like.

Natural evil seems to present a greater theological challenge than moral evil does. Skeptics could agree that God can be excused for the free-will actions of human beings who violate his standard of goodness, but they reason that natural disasters and disease don’t result from human activity. Therefore, this type of “evil” must be attributed solely to God. 

Are Some Forms of Natural Evil Actually Moral Evil?

As I have previously argued, many times natural evil is moral evil in disguise. (See the Resources section below.) In other words, the suffering humans experience stems from human moral failing and poor judgment, not the actual natural phenomenon.

This most certainly seems to be the case when it comes to the Thai liver fluke. Liver cancer caused by parasite infestations would plummet if people stopped eating raw fish and developed better public sanitation systems and practices.

So, is it God’s fault that humans become infected with the Thai liver fluke? Or is it because the people of northern Thailand suffer from poverty and a lack of sanitation—ultimately, conditions caused by human moral failing? Is it God’s fault that people of Southeast Asia develop liver cancer from fluke infestations, when they eat raw and fermented fish instead of properly cooking the meat, knowing the adverse health effects?

Parasites Play a Critical Role in Ecological Systems

Still, the question remains: Why would God create parasites at all?

As it turns out, parasites play an indispensable role in ecosystem health.¹ Though these creatures make minor contributions to the biomass of ecosystems, they have a significant effect on several ecosystem parameters, including biodiversity. In fact, some ecologists believe that an ecosystem becomes more robust and functions better as parasite diversity increases.

Considering this insight, a rationale exists as to why God would create the Thai liver fluke to be a member of the ecosystems of the rivers in Southeast Asia. This parasite infects any carnivore (dogs, cats, rats, and pigs) that eats fish from these rivers, not just humans. Undoubtedly infecting these carnivores influences a variety of ecosystem processes, such as species competition, and energy flow through the ecosystem. The harm this parasite causes humans is an unintended consequence of imprudent human activities—not the inherent design of nature.

Parasites and God’s Providence

Remarkably, recent work by scientists from the Australian Institute of Tropical Health and Medicine (AITHM) indicates that the suffering caused by the Thai liver fluke may fulfill a higher purpose—a greater good.

These researchers believe that the Thai liver fluke may hold the key to effectively treat slow- and non-healing wounds caused by diabetes.²

High blood glucose levels associated with diabetes compromise the circulatory and immune systems. This compromised condition inhibits wound repair due to restricted blood flow to the site of the injury. It also makes the wound much more prone to infection.

The AITHM researchers realized that the granulin-like protein produced by the Thai liver fluke could be used to promote healing of chronic wounds because it promotes rapid cell proliferation in the liver. If incorporated into a cream, this protein could be topically applied to the wounds, stimulating wound repair. This treatment would dramatically reduce the cost of treating chronic wounds and significantly improve the treatment outcomes.

Ironically, the properties of the granulin-like protein that make this biomolecule so insidious are exactly the properties that make it useful to treat diabetics’ wounds. To put it another way, the Thai liver fluke is beneficial to humanity.

The idea that God designed nature to be useful for humanity is a facet of divine providence. In Christian theology, this idea refers to God’s continual role in: (1) preserving his creation; (2) ensuring that everything happens; and (3) guiding the universe. The concept of divine providence also posits that when God created the world he built into the creation everything humans (and other living organisms) would need. Accordingly, every good thing that people possess has been provided and preserved by God, either directly or indirectly.

On this basis, as counterintuitive as this may initially seem, it could be argued that as part of his providence, God created the Thai liver fluke for humanity’s use and benefit.

And we know that in all things God works for the good of those who love him, who have been called according to his purpose.

–Romans 8:28

Check out more from Dr. Rana @Reasons.org