Liver infections are caused by viruses, bacteria, parasites, or fungi that reach the liver through contaminated food and water, blood-to-blood contact, or migration from the gut. Viral hepatitis accounts for the vast majority of cases, with an estimated 304 million people living with chronic hepatitis B or C worldwide as of 2022. But the full picture includes bacterial abscesses, amoebic infections, and fungal pathogens that target people with weakened immune systems.
Viral Hepatitis: The Most Common Cause
Five main hepatitis viruses (A through E) infect the liver, but they spread in fundamentally different ways and carry different risks. Understanding which type you’re dealing with matters because some clear on their own while others can quietly damage the liver for decades.
Hepatitis A and E: Spread Through Contaminated Food and Water
Hepatitis A travels by the fecal-oral route, meaning you get it by swallowing food or water contaminated with stool from an infected person. This can happen through untreated drinking water, raw shellfish harvested from polluted waters, or food prepared by someone who didn’t wash their hands. The virus can also spread through close physical contact, including oral-anal sex. After exposure, symptoms typically appear within 14 to 28 days. Hepatitis E spreads through a similar route and is especially common in regions with poor sanitation. Both viruses cause acute infections that usually resolve without lasting liver damage, though hepatitis E can be dangerous during pregnancy.
Hepatitis B and C: Spread Through Blood and Body Fluids
Hepatitis B and C enter the body through contact with infected blood or other body fluids. For hepatitis B, the most common pathway globally is mother-to-child transmission during birth. It also spreads through unprotected sex with an infected partner, shared or reused needles, needlestick injuries in healthcare settings, and even tattooing or piercing with contaminated equipment. In areas where hepatitis B is highly prevalent, child-to-child transmission during the first five years of life is another significant route.
Hepatitis C spreads primarily through blood-to-blood contact, with shared needles being the dominant risk factor in many countries. What makes hepatitis C particularly concerning is its tendency to become chronic: roughly 70% of people who contract it will develop a long-term infection. Of those, 15% to 30% will progress to cirrhosis (severe scarring of the liver) within 20 years. Only about 30% of people clear the virus on their own within six months. Hepatitis B also becomes chronic in a significant number of cases, particularly when contracted in infancy.
Hepatitis D: A Virus That Needs Hepatitis B
Hepatitis D only infects people who already have hepatitis B. It requires the hepatitis B virus to replicate, so it occurs either as a simultaneous co-infection or as a secondary infection in someone with existing chronic hepatitis B. When both viruses are active, liver damage tends to be more severe and progress faster.
Bacterial Liver Abscesses
Bacteria can reach the liver through the bloodstream, the bile ducts, or directly from an abdominal infection. When they settle in liver tissue, they form pus-filled pockets called pyogenic liver abscesses. The most common culprit is Klebsiella pneumoniae, which was responsible for 76% of culture-positive cases in one large hospital study. E. coli came in second at about 10%, followed by various species of streptococci, staphylococci, and gut-dwelling anaerobic bacteria.
The pathway often starts in the intestine. Klebsiella naturally lives in the gut, and certain antibiotics that kill off competing bacteria without affecting Klebsiella can allow it to overgrow. Animal studies have shown that disrupting the gut’s normal microbial balance with ampicillin-type antibiotics promotes Klebsiella overgrowth, which can then lead to liver abscess formation. Biliary tract disease, recent abdominal surgery, and diabetes are other well-established risk factors.
Parasitic Infections
The amoeba Entamoeba histolytica is the leading parasitic cause of liver infection worldwide. You contract it by swallowing contaminated food or water. Once in the intestine, the active form of the parasite (called a trophozoite) invades the intestinal lining, enters the bloodstream, and gets filtered by the liver. There, it uses specialized surface proteins to latch onto liver cells and destroy tissue, forming large abscesses filled with a characteristic reddish-brown fluid sometimes described as “anchovy paste.” Amoebic liver abscess is most common in tropical and subtropical regions with limited sanitation.
Liver flukes are another parasitic threat. These are flatworms contracted by eating raw or undercooked freshwater fish. They settle in the bile ducts inside the liver, causing chronic inflammation that can persist for years. Long-term infection with certain species is a recognized risk factor for bile duct cancer. Liver fluke infections are concentrated in East and Southeast Asia, where raw fish dishes are part of traditional cuisine.
Fungal and Opportunistic Infections
In people with healthy immune systems, fungal liver infections are rare. But for those who have received a liver transplant or are living with advanced HIV, the liver becomes vulnerable to organisms that the body would normally keep in check.
Candida species are the most frequent fungal invaders, causing 68% to 93% of invasive fungal infections in liver transplant patients. Candida normally lives harmlessly on skin and in the gut and reproductive tract, but when immune defenses are suppressed, it can enter the bloodstream and colonize the liver. Aspergillus, a mold found in soil and decaying matter, accounts for another 1% to 9% of post-transplant fungal infections. Cryptococcal infections make up a smaller share at 0.5% to 5%.
Having a prior cytomegalovirus (CMV) infection significantly raises the risk: transplant patients with CMV are roughly 5.6 times more likely to develop an invasive fungal infection. Drug-resistant Candida strains, including Candida auris (identified in 2009 and now a global concern), have made these infections increasingly difficult to treat.
Environmental and Dietary Toxins
Not all liver damage from external agents involves a living organism. Two environmental contaminants deserve mention because they set the stage for liver disease in ways that often overlap with infection.
Aflatoxins are toxic compounds produced by mold species that grow on staple crops like groundnuts, maize, rice, and sorghum. High temperatures and humidity fuel mold growth, making tropical and subtropical regions most affected. Southeast Asia, sub-Saharan Africa, and parts of South America carry the highest exposure risk. Aflatoxin B1, the most dangerous of the group, may be responsible for between 25,200 and 155,000 liver cancer cases worldwide each year, with an estimated 40% of those in sub-Saharan Africa. When aflatoxin exposure combines with chronic hepatitis B infection, the cancer risk multiplies dramatically.
Microcystins are toxins released by blue-green algae blooms in freshwater lakes and reservoirs. Drinking contaminated water is the most common exposure route, though the toxins can also accumulate in fish and shellfish or become airborne as spray during recreational water activities. Chronic low-level exposure has been linked to liver damage and elevated liver cancer rates in regions of China, Central Serbia, and the southeastern United States.
How Liver Infections Are Detected
Blood tests measuring liver enzymes are typically the first step. Two enzymes, ALT and AST, leak into the bloodstream when liver cells are damaged. Normal ALT ranges from 4 to 36 IU/L, and AST from 5 to 30 IU/L. In acute viral hepatitis, these numbers can spike to more than 15 times the upper limit of normal. Doctors also look at the pattern of elevation: when ALT rises more than other markers like alkaline phosphatase, it points toward direct liver cell damage (the kind infections cause) rather than a blockage in the bile ducts.
Bilirubin, the pigment that causes jaundice, is another key marker. Normal levels sit between 2 and 17 µmol/L. When the liver is inflamed or overwhelmed by infection, it can’t process bilirubin efficiently, and levels rise. Depending on the suspected cause, your doctor may follow up with specific antibody tests for hepatitis viruses, blood cultures to identify bacteria, stool tests for parasites, or imaging like ultrasound or CT to look for abscesses.