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Infectious and Parasitic Liver Diseases

For medical students2 min readUpdated 2026-10-10

Infectious and parasitic liver diseases of non-viral etiology represent a broad group of pathological conditions. Unlike viral hepatitis, these disorders are caused by bacteria, pathogenic spirochetes, protozoa, and various helminthes. In pathomorphological practice, they are characterized by specific tissue changes ranging from focal necrosis and massive hemorrhages to the formation of non-caseating granulomas and mechanical biliary obstruction.

EtiologyDiseases are caused by bacteria, spirochetes, protozoa, and helminthes
LeptospirosisCauses focal fatty change, necrosis, and intrahepatic cholestasis
AscariasisIn 33% of patients, worms obstruct the common bile duct, causing cholangitis
GranulomasNon-caseating granulomas form in the liver in sarcoidosis and schistosomiasis

Leptospirosis (Weil's Disease)

Leptospirosis, also known in clinical practice as icteric leptospirosis or Weil's disease, is a severe infection with prominent systemic manifestations.

Etiology and Epidemiology: The causative agent is the pathogenic spirochete Leptospira icterohaemorrhagiae. Rats serve as the primary reservoir in endemic foci. Human infection occurs via three routes: through the skin, respiratory tract, or digestive tract. Occupational risk groups include individuals in contact with contaminated water and soil, such as sewage and irrigation workers, farmers, and fishermen. The incubation period ranges from 10 to 15 days.

Clinical and Morphological Features: The disease is generalized. Patients develop jaundice, conjunctivitis, lymphocytic meningitis, and hemorrhagic diathesis. The infection causes renal tubular epithelial damage, as well as focal necrosis of the myocardium and skeletal muscle.

Liver Microscopy: Histological examination reveals:

Prognosis: Mortality in leptospirosis reaches 15%. During the first week, patients may die from hemorrhagic pulmonary consolidation, while in later stages, renal failure becomes the cause of death.

Hepatobiliary Ascariasis

Ascariasis is a parasitic intestinal infection caused by the roundworm Ascaris lumbricoides.

Epidemiological Features: This helminthiasis is most prevalent among children. Endemic regions with the highest incidence traditionally include countries in Africa and the Far East.

Pathogenesis and Complications: Although the primary habitat of the parasite is the intestine, the disease poses a serious threat to the liver and biliary tract. In one-third of infected patients, adult ascarids migrate and invade the common bile duct. This condition inevitably leads to mechanical biliary obstruction and the subsequent development of severe inflammation—cholangitis.

Granulomatous Liver Disease

Pathologies accompanied by a productive granulomatous reaction warrant special attention. Their key morphological feature is the formation of non-caseating granulomas, which are nodules lacking caseous necrosis in their center.

Primary Liver Diseases: Granuloma formation is driven by primary conditions such as primary biliary cholangitis (PBC) and the parasitic disease schistosomiasis.

Secondary Involvement: In most cases, hepatic granulomas reflect generalized systemic processes. The most frequent cause is sarcoidosis. Secondary granulomatous inflammation is also triggered by various fungal infections, rickettsial diseases, and parasitic infestations.

Other Factors: Beyond infectious and autoimmune agents, a productive granulomatous reaction in hepatic tissue can be of allergic or drug-induced origin.

Mnemonic

To remember the risk groups for leptospirosis, think of contact with wet environments where infected rats reside (e.g., fishermen, sewage workers, agricultural field workers).

Frequently asked questions

What pathomorphological changes develop in extrahepatic organs during leptospirosis?

Leptospirosis affects multiple extrahepatic organs due to generalized capillarotoxicosis and hemorrhagic syndrome.

  • Kidneys — interstitial nephritis, tubular necrosis, and acute renal failure in severe cases.
  • Skeletal muscle — edema, myofibrillar vacuolization, focal necrosis, hemorrhages, and histiolymphocytic infiltrates.
  • Heart — myocarditis, petechial epicardial hemorrhages, pericardial effusion.
  • Lungs — hemorrhages, pneumonia.
  • Eyes — conjunctivitis, scleritis, hemorrhages, iritis, iridocyclitis, uveitis.
  • Adrenal glands — hemorrhages.
  • CNS — perivascular inflammation, serous meningitis, meningoencephalitis, hemorrhages, cerebral edema.

Erythrocyte hemolysis is also observed.

Which helminthiases, besides ascariasis and schistosomiasis, cause parasitic liver lesions?

In addition to ascariasis and schistosomiasis, parasitic liver lesions are caused by the following helminths:

  • Echinococcosis (Echinococcus granulosus) — hydatid cyst formation with a chitinous shell, brood capsules, and scolices inside.
  • Alveococcosis (Echinococcus multilocularis) — multilocular echinococcosis with infiltrative nodular growth of multiple small vesicles, prone to central necrosis and tumor-like metastasis.
  • Opisthorchiasis (Opisthorchis sinensis) — biliary tract infection with secondary purulent inflammation and adenomatous hyperplasia of the bile duct epithelium, considered a background condition for cholangiocarcinoma.

Hepatic echinococcosis and opisthorchiasis are also listed among the causes of secondary biliary cirrhosis.

Which protozoa cause infectious liver lesions?

The following protozoa are known to cause liver lesions:

  • Entamoeba histolytica — can cause amoebic liver abscess as a complication of amoebic dysentery.
  • Plasmodium — the malaria parasite; acute malaria causes hepatomegaly, with the liver appearing enlarged, hyperemic, and dark gray on cross-section. Microscopy reveals Kupffer cell hyperplasia and deposition of hemozoin (hematin) and hemosiderin pigment; chronic infection leads to marked hepatic fibrosis.

The dark gray discoloration of the liver in malaria is due to the malarial pigment hemozoin, produced during the parasite's digestion of hemoglobin.

What are the main causes of death in severe leptospirosis?

The overall mortality rate for Weil's disease is about 15%. If a patient dies in the first week, the cause is usually hemorrhagic pulmonary consolidation. In later stages, critical renal tubular epithelial damage leading to renal failure becomes the primary factor.

What is the primary danger of ascariasis to the liver?

The roundworm Ascaris lumbricoides primarily infects the intestine. However, in 33% of infected patients, helminthes invade the common bile duct, causing obstruction and precipitating cholangitis.

Which systemic diseases most frequently cause hepatic granuloma formation?

Secondary granulomatous liver lesions reflect generalized systemic processes. Sarcoidosis is the most common cause. Additionally, fungal infections, rickettsial diseases, and parasitic infestations can trigger this reaction.

What is the key morphological feature of granulomas in these conditions?

The main pathomorphological characteristic of granulomas in primary biliary cholangitis, sarcoidosis, and schistosomiasis is their non-caseating nature, meaning there is a complete absence of central caseous necrosis within the inflammatory nodule.

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