Non-Hepatotropic Viral, Bacterial and Parasitic Infections of the Liver

Yellow fever

Yellow fever (YF) is a member of the Flaviviridae family of viruses and is endemic in tropical Africa and South America, where the Aedes and Haemagogus mosquito vectors reside. The true incidence of disease remains unknown, but the World Health Organization (WHO) has estimated that 84,000 to 170,000 cases and up to 60,000 deaths occur annually, the majority in Africa. Disease outbreaks are more often reported in West Africa, particularly in areas where mass vaccination campaigns have been interrupted, but large outbreaks have also erupted in Uganda, Sudan and Ethiopia. ^, Severe re-emergence events have also occurred in Brazil where nonendemic areas have experienced major outbreaks with case fatality rates up to 43%. In a 2017–2018 outbreak of YF in Brazil, among the 2585 reported cases, 571 cases were confirmed in Sao Paulo, the most developed state. The YF pattern was ‘rural’ or sylvatic but cases emerged in the neighbourhoods of large cities.

Approximately 30% of those infected with YF will manifest symptoms. The clinical stages of disease (acute infection, remission, intoxication) begin with sudden onset of fever and headache associated with nausea and vomiting lasting 3–4 days; high fever can be accompanied by paradoxical bradycardia (Faget sign). Liver enzymes are modestly elevated early in the disease. Symptoms may resolve for up to 2 days but return in the stage of ‘intoxication’ with fever, vomiting and jaundice. During this stage, aminotransferase levels are greatly elevated. Aspartate transaminase (AST) is typically higher than alanine transaminase (ALT), unlike in viral hepatitis, which shows the reverse profile. In the third and final stage of disease, patients develop jaundice, severe coagulopathy and a bleeding diathesis leading to multiorgan failure and death. There is no specific treatment for YF apart from supportive care. The diagnosis can be suspected based on clinical features and travel history and is usually confirmed by the serological demonstration of specific immunoglobulin M (IgM) using enzyme-linked immunosorbent assay (ELISA). Specialized testing of tissue samples using IHC or viral culture can also be performed by the CDC.

At autopsy, the gross appearance of the liver belies the microscopic severity of disease, as the liver typically maintains its size (or is slightly enlarged) and contour. If autopsy is performed on patients promptly after death, the external surface of the liver is typically reddish grey, but if autopsy is delayed for 6–12 hours, the surface may appear yellow. On cut section, the parenchyma is also variably yellow due to steatosis ( Fig. 7.1A ). Microscopically, the classic histopathological features include hepatocyte swelling, confluent midzonal necrosis with sparing of periportal and centrizonal hepatocytes, and steatosis. Inflammation is scant, and cholestasis is unusual. Apoptosis is the predominant mechanism of cell death and is manifested by acidophilic degeneration of hepatocytes with loss of nuclei forming the classic but nonspecific acidophilic (‘Councilman–Rocha Lima’) bodies ( Fig. 7.1B, C ). The preferential midzonal localization of apoptosis can be attributed to direct injury by virus, hypoxia and cell-mediated immunity. Rarely, eosinophilic intranuclear inclusions (Torres bodies) are present. Immunohistochemical stains highlight the distribution of abundant YF antigens in hepatocytes and Kupffer cells throughout the hepatic midzone ( Fig. 7.1D ). Electron microscopy (EM) can be used to demonstrate the ultrastructural characteristics of the 40-nm virions ( Fig. 7.1E ). Fatty change, particularly prominent in the perivenular zone, is typical of YF and includes large- and small-droplet macrovesicular steatosis, as well as microvesicular steatosis, the latter demonstrated by EM. The surviving liver shows hepatocyte swelling and regenerative hyperplasia with frequent multinucleated hepatocytes. A mild portal-based lymphocytic infiltrate may be observed, but inflammation is generally minimal. In their detailed series of 93 YF autopsies, Klotz and Belt did not observe a correlation between the clinical severity of disease and the extent of liver injury.

Although a prompt and complete hepatic recovery is anticipated to occur in patients who survive an attack of YF, a nonspecific lobular hepatitis was described in 1972 during an epidemic in Nigeria, in four patients biopsied from 16 to 62 days after the onset of acute illness; the authors thus suggested that liver damage associated with YF infection can persist, and healing may not be as rapid as previously thought. In a more recent study of the 2017–2018 Brazilian YF outbreak, Casadio et al. reported on the follow-up of 58 patients who survived severe acute YF and were negative for YF-RNA at the time of hospital discharge; these patients were followed as part of a clinical trial of sofosbuvir for the treatment of acute YF. Twenty-six (45%) of the patients in the trial presented with clinical and/or laboratory evidence of late-onset relapsing hepatitis, defined as a new elevation in aminotransferase levels within 6 months after the original improvement of liver function. The interval from hospital discharge to the new ALT peak was 59 ± 19 days and the duration of the altered ALT level ranged from 51 to 176 days. Nine of these 26 cases underwent liver biopsy, and the liver showed lobular necroinflammation, with many foci of spotty necrosis. Apoptosis and hydropic regeneration were found in all lobular zones, without the typical midzonal lesions of YF. Some of the patients had confluent necrosis and Kupffer cell hypertrophy was present in all cases. Unlike the immunohistochemical pattern of classic acute YF, immunohistochemical detection of YF antigens in all nine late-onset relapsing hepatitis cases was mainly localized to the cytoplasm of Kupffer cells. All 26 patients with late-onset relapsing hepatitis recovered clinically with normal levels of liver enzymes. These findings may substantiate a longer period of observation postinfection.

Orthotopic liver transplantation (OLT) was performed in seven cases from the 2017–2018 Brazil outbreak. Three patients recovered, but four patients died. Autopsies revealed characteristic histological features of YF hepatitis in all engrafted livers. YF antigen was detected by IHC in the heart in one case, liver and testis in three cases and the kidney and spleen in all four fatal cases. YF virus RNA was also detected by reverse-transcriptase polymerase chain reaction (RT-PCR) in the liver and in other organs in all of the fatal cases. These findings suggest that infection of the engrafted liver and other organs by YF, possibly combined with major ischaemic systemic lesions, may have led to the death of four of the seven patients undergoing OLT.

A live, attenuated YF vaccine is available for those living in countries where YF is endemic and for international travellers. Although serious adverse reactions to the vaccine are rare, cases of ‘YF vaccine-associated viscerotropic disease’ (YEL-AVD) emerged in 2001 and have been reported in countries worldwide, with an estimated incidence of 0.4 cases per 100,000 doses of vaccine. YEL-AVD is characterized by multiorgan failure and a high-level viraemia that can reach 1000 times greater than levels expected for vaccination alone.

There are notable histopathological and immunohistochemical differences between wild-type YF virus infections and YEL-AVD. In wild-type disease, inflammation is minimal and hepatic necrosis predominates; on IHC, YF antigens are detected in the liver and are predominantly localized within necrotic hepatocytes. In contrast, the features of YEL-AVD include a prominent portal-based mononuclear and sinusoidal infiltrate in the absence of confluent necrosis ( Fig. 7.1F ). On IHC in YEL-AVD, YF viral antigens are detected in portal-based mesenchymal cells as well as Kupffer cells lining hepatic sinusoids (also similar to the pattern seen in late-onset relapsing hepatitis). Importantly, viral antigens in YEL-AVD are also detected throughout visceral organs ( Fig. 7.1G ), unlike in wild-type disease, where antigens are limited to the liver.

The pathogenesis of YEL-AVD has not been fully elucidated. No definitive genetic predisposition has been identified in affected patients, and no significant mutations that alter the virulence of the vaccine strains have been detected. Studies have shown that those with thymic disease and individuals over age 60 harbour a greater risk of YEL-AVD, ^, but this adverse reaction has also been reported in patients as young as 4 years old and those without known underlying disease.

Dengue

Dengue virus is another flavivirus and is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. Initial exposure to one of the five viral serotypes can be asymptomatic or can result in dengue fever, a self-limiting influenza-like illness with symptoms of fever, rash, arthralgias and myalgias (‘breakbone fever’). The clinically more severe diseases, dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS), now defined as severe dengue, are caused by reinfection with a viral serotype that differs from the first infection. The pathogenesis of severe dengue is complex, including, among others, recent demonstration of strong systemic proinflammatory response. Thrombocytopenia leads to widespread petechial haemorrhage, capillary leakage and fluid depletion, resulting in multiorgan failure. ^, Children are disproportionately affected by severe dengue. Untreated, the mortality approaches 30%.

In DHF/DSS or severe dengue, the liver at autopsy is enlarged, pale from steatosis and blotchy from multifocal haemorrhage. None of the histopathological features seen in DHF/DSS is considered pathognomonic. Microscopically, there are variable amounts of spotty, confluent perivenular or midzonal hepatic necrosis, with little or no inflammation; cell death is through apoptosis ( Fig. 7.2A ). As with other VHFs, acidophilic bodies and steatosis may also be seen. On IHC, dengue viral antigens are predominantly identified within Kupffer cells ( Fig. 7.2B ), in contrast to YF, where hepatocytes are preferentially infected.

Ultrastructural findings in the liver have been described in a series of seven autopsy cases in children ages 3–9 years with fulminant DHF who died within the first week of illness. The features included abundant lysosomes with varied content and sizes, vacuolization, steatosis and damaged and swollen mitochondria with distorted or damaged cisternae as evidence of cellular injury. The endoplasmic reticulum and Golgi system showed dilated cisternae or vesicle formations. Viral particles were rarely found, however, and not in arrays within vesicles as previously reported in experimental infections. Although there was ample evidence of hepatocyte damage, no viral-induced replicating structure was identified in this study. Thus, in DHF, the evolution of liver injury in fulminant DHF may occur independent of active viral replication, but this remains an area of further study.

Lassa fever and other arenaviruses

Arenaviruses are classified into two broad groups: Old World viruses identified in the Eastern Hemisphere, such as Lassa virus and lymphocytic choriomeningitis virus (LCMV), and New World viruses identified in the Western Hemisphere, such as Junin virus and Machupo virus. This family of viruses is transmitted by various rodent species, but some viruses (e.g. Lassa, Machupo, Lujo) can also be spread from person to person. Most arenaviral infections cause a flu-like illness, but haemorrhagic fever (HF) syndromes can be caused by infections with LCMV, Junin virus (Argentine HF), Machupo virus (Bolivian HF), Guanarito virus (Venezuelan HF), Sabia virus (Brazilian HF), Chapare virus (Chapare HF) and Lassa virus. ^,

Lassa virus was first described in the late 1960s and is the most common arenavirus. The natural reservoir of Lassa virus is the multimammate rat, Mastomys natalensis , and humans are infected by direct exposure to its urine. After the alarming emergence of the disease in the early 1970s, serological surveys have shown that the infection is widespread in West Africa; however, clinical disease occurs in 5–10%, and the case-fatality rate is <25%. The clinical features include abdominal pain, pharyngitis and fever, but not jaundice. Hepatitis is common in Lassa fever but is mild or absent in the South American HFs. In contrast, haemorrhage, neurological involvement, leukopenia and thrombocytopenia are more often seen in the South American HFs than in Lassa fever.

Grossly, arenavirus infections cause mottling of the liver ( Fig. 7.3A ). Histologically, there is pauci-inflammatory necrosis, and individual hepatocytes or groups of cells throughout the acini appear acidophilic ( Fig. 7.3B ). There is no cholestasis or steatosis, but lipofuscin deposition is evident. Arenaviruses can be seen on EM, but there are no light microscopy viral inclusions. On IHC, abundant viral antigens can be seen lining hepatocytes and sinusoids ( Fig. 7.3C ).

The histopathological features of other arenaviral infections, including Argentine HF (Junin virus) and Bolivian HF (Machupo virus), are strikingly similar ( Fig. 7.4A–C ). Lujo virus is a novel, highly fatal arenavirus first identified in southern Africa in 2008 and is named for the cities involved in the disease outbreak (Lusaka and Johannesburg) ( Fig. 7.4D, E ). LCMV was the first arenavirus discovered and isolated in 1933 and is distributed worldwide. Infection can be asymptomatic in immunocompetent hosts but can cause severe disease, most notably aseptic meningitis, in immunosuppressed patients. Outbreaks of severe LCMV infection have been described in transplant recipients ^, ( Fig. 7.4F–H ).

Ebola and Marburg viruses

Viruses of the Ebolavirus and Marburgvirus genera (family Filoviridae) cause sporadic outbreaks of HF in Africa with high case-fatality rates. Marburg virus disease (MVD) was identified first in 1967 when a small cluster of laboratory workers in the university town of Marburg, Germany, became sick after working with African green monkeys imported from Uganda. Subsequent isolated cases occurred in Kenya and South Africa up until 1982, followed by sporadic outbreaks in the Democratic Republic of the Congo (DRC) and Angola in 1998 and 2004; an isolated case occurred in November 2014 in Uganda. Ebola virus disease (EVD) was first identified in 1976 in Yambuko, DRC, but was named after the Ebola River to the north. EVD is caused by one of four Ebolavirus species ( Zaire, Sudan, Tai Forest, Bundibugyo ), but Zaire ebolavirus is the most virulent. The virus known as Reston ebolavirus does not cause disease in humans, and swine have been identified as the natural hosts. Filovirus outbreaks and large epidemics are perpetuated by person-to-person transmission. Although the source of filoviruses in nature has not been definitively identified, the cumulative evidence implicates bats as reservoirs. ^, The clinical manifestations of MVD and EVD include vomiting, fever, widespread haemorrhage, shock and disseminated intravascular coagulation.

The hepatic pathology of filoviruses is similar to that of other VHFs; there is variable spotty to confluent hepatocyte necrosis with minimal inflammation and no cholestasis. ^, Characteristic eosinophilic and filamentous intracytoplasmic viral inclusions can be identified within hepatocytes and are usually numerous in EVD ( Fig. 7.5A ). The viral inclusions and distribution of antigens can be confirmed by IHC ( Fig. 7.5B ). Ultrastructurally, the inclusions are composed of aggregates of viral nucleocapsids ( Fig. 7.5C ). Experimental studies show that the Ebola virus is present in large quantities free in the blood, throughout the mononuclear phagocyte system, in endothelial cells and in hepatocytes; the reticular network of lymph nodes is also heavily infected and damaged.

Filovirus infections remain critically relevant. In 1995, 2000, 2007 and 2008, large Ebola virus outbreaks occurred throughout the DRC and Uganda, resulting in high mortality. The largest reported outbreak of EVD erupted in March 2014 in Guinea. The virus spread rapidly throughout West Africa, igniting an international public health emergency and resulting in more than 28,000 infections and 11,000 deaths. The potential for patients with VHF to travel to industrialized countries ^, was also realized during the 2014 Ebola epidemic, when a small number of imported cases occurred in Europe and the United States. ^, The more recent EVD outbreak in eastern DRC, which began in August 2018, was the world’s second largest, with a case-fatality rate of 66%, and was declared over in June 2020 as a new Ebola virus outbreak erupted in the west ( https://www.cdc.gov/vhf/ebola/outbreaks/drc/2018-august.html ).

Multiple Ebola vaccine candidates have been developed, as well as new therapeutic treatments, and four African countries now have licensed Ebola vaccines ( https://news.un.org/en/story/2020/02/1057461 , accessed 18 November 2020).

Crimean-Congo haemorrhagic fever and Rift Valley fever viruses

Crimean-Congo HF (CCHF) virus formerly belonged to the Bunyaviridae family and is now classified within the Nairoviridae family. CCHF is endemic in various countries in Africa, Asia and Eastern Europe. CCHF has emerged as an important human pathogen, probably as a result of improvements in surveillance and increased awareness. The clinical and histopathological features are similar to those of other VHFs ( Fig. 7.6A ). IHC and in situ hybridization (ISH) analysis show that mononuclear phagocytes, endothelial cells and hepatocytes are the main targets of infection ( Fig. 7.6B ). Rift Valley fever, family Phenuviridae , is another bunyavirus reported mainly in eastern and southern Africa, Egypt, Madagascar and the Arabian peninsula. The changes in the liver in this disease are similar to those seen in other VHFs. Midzonal necrosis is a common feature seen, and IHC can also help establish the diagnosis ( Fig. 7.6C, D ).

Herpes simplex viruses

Primary HSV infection produces oral or genital lesions and remains latent in neural ganglia for life. There are two strains of HSV: type 1 was previously more often associated with orolabial lesions, whereas type 2 more often caused genital lesions. However, recent data indicate that HHV1 is now the predominant cause of genital herpes lesions. Primary genital herpes infections can be asymptomatic or can produce vesicles on an erythematous base, reflecting viral replication within epithelial cells. After ascending sensory nerves, the virus enters a period of latency in the dorsal root ganglia. Genital infections in pregnant women can be transmitted to the developing fetus or neonate. Congenital transmission results in a triad of clinical features: cutaneous lesions, neurological abnormalities (e.g. microcephaly) and ocular disease (e.g. chorioretinitis). If HSV is acquired peripartum or postpartum, disease in the neonate may lead to skin, eye and mouth lesions (45% of cases), central nervous system (CNS) disease (30%) or disseminated disease (25%) with necrotizing hepatitis. Immunocompromised patients are also particularly at risk for severe fulminant systemic herpes infection. Fatal herpetic hepatitis is also reported in apparently immunocompetent adults. The clinical features resemble those of septic endotoxic shock; jaundice is not always present.

At autopsy, the liver in disseminated disease is enlarged and mottled with multiple yellow or white necrotic foci surrounded by congestion. Microscopically, there is irregular parenchymal coagulative necrosis with minimal, predominantly lymphocytic, portal-based inflammation ( Fig. 7.12A ). At the margins of necrotic zones, some hepatocytes display the classic amphophilic Cowdry type A intranuclear inclusions, with a clear halo and peripheral margination of chromatin, while surrounding hepatocytes show nuclear basophilia. Regenerative and reactive features are manifested by hepatocyte multinucleation and Kupffer cell hypertrophy ( Fig. 7.12B, E and F ). Unlike the distribution of necrosis in YF and the viral hepatitides, the necrotic foci in herpes infections appear to expand contiguously or ‘centrifugally’. IHC is useful in the diagnosis of HSV infections but cannot differentiate between types 1 and 2 ( Fig. 7.12C ). PCR on formalin-fixed tissues can be used to distinguish the two strains. EM reveals abundant virions in nuclei of infected hepatocytes ( Fig. 7.12D ).

Herpes zoster

Varicella-zoster virus (VZV) causes chickenpox and, as a reactivation of latent infection, shingles. After infection there is a primary viraemia with viral replication in the epithelium of the gut, respiratory tract, liver, pancreas and adrenal glands. A secondary viraemia leads to skin infection manifested by the classic fluid-filled blisters that form scabs. In adults and children, liver disease is usually restricted to immunocompromised patients. In pregnant women, intrauterine infections can result in severe outcomes (congenital varicella syndrome), and perinatal infections can cause disseminated disease with necrotizing hepatitis. In rare cases, corticosteroid therapy given during the phases of viral dissemination may precipitate severe zoster. We report one such fatal case; a 24-year-old man with a history of asthma developed pneumonia refractory to medical therapy and progression of disease to severe coagulopathy and liver failure. The histopathological manifestations in the liver in severe or fatal infections such as this case resemble those of herpes simplex infections, with focal or massive liver necrosis and minimal inflammation. Intranuclear inclusions may be abundant, as in this case ( Fig. 7.13A, B ), or rare. An immunohistochemical assay targeting VZV shows staining in a membrane and cytoplasmic pattern, confirming the diagnosis ( Fig. 7.13C ). EM shows abundant herpes virions ( Fig. 7.13D ). PCR assays, even when performed on FFPE material, are highly sensitive and specific.

Cytomegalovirus

Most adult populations have a prevalence of latent, asymptomatic CMV infection greater than 50%, as judged by serological surveys. Primary infection and clinically significant disease can occur in immunocompetent adults, but the most significant CMV infections occur in infants (as one of the ‘TORCH’ [toxoplasmosis, other agents, rubella, CMV, herpes simplex] infections) and in immunocompromised patients. In renal transplant recipients, CMV is the most common specific cause of hepatitis; in liver transplant recipients, CMV hepatitis needs to be distinguished from graft rejection (see Chapter 14 ).

In immunocompetent individuals, CMV can produce an infectious mononucleosis-like syndrome. Liver biopsy shows focal hepatocyte and bile duct damage with lymphocytic infiltration of the sinusoids. In some cases, noncaseating epithelioid cell granulomas are observed, but viral inclusions or immunohistochemically demonstrable antigen may be absent. ^,

CMV is one cause of neonatal hepatitis, with giant cell transformation, cholestasis and inflammation. The characteristic finding is an enlarged cell (endothelial, hepatocyte or bile duct epithelial) with an amphophilic intranuclear inclusion surrounded by a clear halo, resembling an owl’s eye, and basophilic granules in the cytoplasm. Both the nuclear and the cytoplasmic inclusions represent closely packed virions ( Fig. 7.14 ).

In immunocompromised hosts, CMV inclusions are often seen without necrosis or inflammation—a ‘passenger infection’—but when tissue damage is evident, the virus is presumed to be pathogenic. In the fetal liver, CMV disease has been associated with obliteration of bile ducts, but there is no evidence that it plays a significant role in syndromic or nonsyndromic paucity of intrahepatic bile ducts (see Chapter 3 ).

Epstein–Barr virus

In the tropics, EBV is transmitted early in childhood and is aetiologically associated with Burkitt lymphoma. In industrialized countries, clinically significant infections usually occur in adolescence or adulthood and cause a self-limited, acute infectious mononucleosis characterized by pharyngitis, fever, rash and cervical lymphadenopathy together with splenomegaly and hepatomegaly in some cases. Transient elevations in transaminase levels occur in the majority of patients, but jaundice is rare. Acute infectious mononucleosis is typically diagnosed clinically, but liver biopsy may be performed in cases with atypical clinical presentations and/or laboratory findings. Histologic sections show expansion of portal tracts by a lymphocyte-predominate inflammatory infiltrate with admixed plasma cells and eosinophils. The sinusoids classically show a diffuse lymphocytic infiltrate arranged in a linear ‘string of beads’ pattern, while the overall lobular architecture is generally preserved. ^, When the inflammatory infiltrate is marked, endophlebitis is observed, and focal apoptotic hepatocytes (spotty necrosis) can be identified, although fulminant hepatitis is rare. The inflammatory infiltrate is composed predominantly of reactive T lymphocytes and natural killer (NK) cells, whereas EBV-infected B lymphocytes are rare. The sinusoidal lymphocytes can appear atypical, raising suspicion for leukaemia/lymphoma. Larger immunoblastic cells morphologically similar to Hodgkin/Reed–Sternberg (HRS) cells can occasionally be identified and will similarly express CD30, EBV-latent membrane protein and EBV-encoded RNA (EBER); however, unlike in Hodgkin lymphoma, the HRS-like cells in infectious mononucleosis are CD15 negative. ^, Steatosis may occur in EBV infections, but cholestasis is not a typical feature ( Fig. 7.15C ). Non-necrotizing granulomas and fibrin-ring granulomas are occasionally found in infectious mononucleosis. EBV can be detected in the liver using ISH targeting EBER. The nuclei of infected B lymphocytes are highlighted using this technique, but again, these are rare amid the background of a predominantly T-lymphocyte infiltrate.

Autoimmune serologies (typically anti-smooth muscle antibody and less commonly antinuclear, mitochondrial, microsomal and reticulin antibodies) can be elevated in patients with EBV hepatitis, raising concern for autoimmune hepatitis. However, the lack of a significant plasma cell infiltrate and the absence of confluent or bridging necrosis, together with EBV viral capsid antigen serologic testing, can help differentiate EBV hepatitis from autoimmune hepatitis.

Human herpesvirus 6

Unlike EBV, HHV6 infects T cells. Primary infection in children usually causes transient fever and skin rash (erythema subitum). Occasionally, severe visceral infection can result, including hepatitis and haemophagocytic syndrome. This can occur in transplant recipients and other immunosuppressed patients (including those with HIV/AIDS) and occasionally in immunocompetent persons. The histopathology is of a nonspecific lobular hepatitis. Syncytial giant cell transformation of bile ductular epithelium has been described in a heart transplant recipient.

Typhoid fever

Salmonella typhi is a Gram-negative bacillus. The classic clinicopathological phases of typhoid disease are incubation, active invasion (dissemination throughout the lymphoreticular system), fastigium and lysis. During the phase of invasion, the liver shows a range of nonspecific histological lesions: sinusoidal and portal lymphocytosis, focal parenchymal necrosis and Kupffer cell hypertrophy, sometimes with erythrophagocytosis. Small macrophage clusters, which evolve into non-necrotizing epithelioid cell granulomas, are often seen. Small-droplet macrovesicular steatosis in hepatocytes is common. In the symptomatic phase of fastigium, there is hepatomegaly and sometimes jaundice. The granulomas in the liver enlarge and become necrotic, as they do in the lymph nodes of the bowel and mesentery ( Fig. 7.29 ). There are no Langhans giant cells, and bacilli are very difficult to detect with standard methods such as Gram stain. Although typhoid bacilli multiply readily in the bile and gallbladder, ascending cholangitis is rare.

Brucellosis

Brucellosis is a zoonosis of ruminants caused by Brucella melitensis , Brucella abortus or Brucella suis . Humans may become infected by the Gram-negative bacilli from occupational exposure or ingestion of unpasteurized milk products. The clinical manifestations are protean; brucellosis is a great mimic. The three main clinical patterns, acute, recurrent and chronic, all include fever and weakness. In all patterns, there is haematogenous dissemination of bacteria to lymphoreticular organs, including the liver. Hepatomegaly and altered LFTs are common.

Histological examination shows a nonspecific reactive hepatitis with microgranulomas or epithelioid cell granulomas in portal areas and throughout the lobules ^, ( Fig. 7.30 ). The latter may have giant cells and in the chronic pattern of brucellosis, there may be fibrinoid necrosis, rendering the histological appearance indistinguishable from TB or histoplasmosis. Necrosis is uncommon, and cholestasis is not typically seen. Patients with large caseous granulomas (‘coin lesions’) in the liver have been reported. When granulomatous hepatitis without evident cause is encountered in biopsy material, brucellosis should always be considered. Serological testing is the means of establishing the diagnosis.

Melioidosis

Disease caused by the Gram-negative bacillus Burkholderia (formerly Pseudomonas ) pseudomallei is endemic in Southeast Asia and the Indian subcontinent, and sporadic cases occur in other parts of the tropics and subtropics (although not in Africa). ^, The organism is a saprophyte of soil and water. Clinically, melioidosis presents as acute pulmonary, septicaemic or chronic suppurative disease. The acute infections are rapid and have high mortality; hepatomegaly and jaundice are features. In acute melioidosis, the liver shows small and large abscesses, the rods of which may be seen on silver stain ( Fig. 7.31 ). In chronic melioidosis, necrotic granulomas may mimic TB or may be stellate in form, resembling cat-scratch disease. Bacteria are rarely seen.

Listeriosis

Listeria monocytogenes is a Gram-positive bacillus that is saprophytic in soil and water. It may be transmitted to humans through the consumption of contaminated foods such as soft cheeses. Disease occurs in pregnant women and their infants by the transplacental route, in immunosuppressed patients and less often in immunocompetent individuals. HIV infection does not play a predisposing role. The clinical disease in neonates is septicaemia with multiple organ lesions. The liver shows miliary microabscesses that contain abundant Gram-positive rods ( Fig. 7.32 ). In routine sections, this may resemble acute neonatal syphilis. In adults with listeriosis the clinical picture can mimic viral hepatitis, although microabscesses with bacilli are common, and some patients have a granulomatous hepatitis.

Syphilis ( Treponema pallidum )

Congenital syphilis often manifests early as intrauterine death or infantile disease, both with hepatosplenomegaly. In the earlier phases there may be miliary necroses, portal inflammation and hepatocyte giant cell transformation. In neonatal deaths the degree of persistent haemopoiesis is excessive for gestational age. Warthin–Starry stain demonstrates large numbers of spirochaetes, particularly in the setting of necrosis. Later the liver shows a characteristic progressive pericellular fibrosis with apparent withering of the liver cell plates ( Fig. 7.37A, B ). Immunohistochemical staining is extremely useful in confirming the diagnosis ( Fig. 7.37C ).

Primary syphilis has no notable liver histology, but in the secondary phase there is focal hepatocyte necrosis, portal inflammation with numerous polymorphs around bile ductules and sometimes granulomas. The portal vessels may show vasculitis. ^, Spirochaetes are less conspicuous than congenital lesions. The lesion of tertiary disease is the gumma ( Fig. 7.38A ). In the liver, gummas are single or multiple, ranging in size from millimetres to centimetres. Gummas are tuberculoid giant cell granulomas with amorphous, pale, necrotic centres, mimicking caseation, although the classic description emphasizes the preservation of cellular architecture within the necrotic zone. Accompanying this are plasma cells and endarteritis obliterans. Healing is by fibrosis with broad bands of scarring, which may distort the liver to produce ‘hepar lobatum’ ( Fig. 7.38B ).

Relapsing fever (borreliosis)

Relapsing fever may be louse- or tick-borne and is caused by many Borrelia spp. The louse-borne infection is caused by Borrelia recurrentis . Most infections occur in East Africa. As the name suggests, relapsing fever presents as periodic fever lasting 1 week and recurring another week or so later. The diagnosis is made by finding the spirochaetes in peripheral blood smears. In severe infections, jaundice and hepatosplenomegaly occur. In fatal cases an enlarged, congested liver is seen. There are foci of hepatocyte necrosis with surrounding haemorrhage in acinar zones 2 and 3. The sinusoids are infiltrated by lymphocytes and polymorphs, which are associated with Kupffer cell hypertrophy and erythrophagocytosis. Warthin–Starry or Dieterle stains may reveal the 10–20-µm-long spirochaetes lying free in the sinusoids.

Leptospirosis (Weil disease)

Leptospirosis is a zoonosis of rats, dogs and pigs. The agent, Leptospira icterohaemorrhagica , is ubiquitous in wet environments, and humans acquire the infection by exposure to water contaminated with animal urine. The clinical features are fever with jaundice and renal failure and bleeding into conjunctiva, skin and viscera. Hepatomegaly is often present. The haemorrhagic phenomena are not caused by liver failure but by direct damage to small vessels by leptospirae. With appropriate therapy, mortality is now low.

At autopsy the liver may be normal or enlarged and icteric. The major histological features are individual hepatocyte damage, regeneration, canalicular cholestasis and only slight portal or sinusoidal lymphocytosis. Ballooning and hydropic change of hepatocytes are less marked than in viral hepatitis; apoptotic bodies are the more prominent evidence of liver damage. Many liver cells are binucleate and show mitoses; variation in size is a further indication of regenerative activity. Autopsy material shows dissociation and separation of liver cell plates ( Fig. 7.39A ), but biopsy samples usually show intact plates.

Kupffer cells are hypertrophied and contain erythrocytes. In some cases of leptospirosis, a Warthin–Starry stain shows the spirochaetes, which are 10–20 µm long ( Fig. 7.39B ). Immunohistochemical staining with specific polyclonal antibodies can demonstrate leptospiral antigens in Kupffer cells, portal tracts and endothelium ( Fig. 7.39C, D ).

Regarding disease pathogenesis, evidence from a decade of studies using human and animal samples as well as cell lines has shown that the adhesion of pathogenic Leptospira spp. to endothelial as well as epithelial cells mainly occurs through the binding of bacterial lipoproteins to host E-cadherin and VE-cadherin. ^, Recently, a leptospiral lipase was characterized and was detected by IHC on membranes of hepatocytes from human autopsies. This lipase, hypothetically secreted by leptospires during cell adhesion, might be relevant in cell disruption, chiefly in the liver and possibly also in other organs.

Lyme disease

Lyme disease is a multisystem tick-borne infection caused by Borrelia burgdorferi and the closely related species Borrelia mayonii , the latter being first identified in 2013. Whereas B. burgdorferi is found throughout Europe, Asia and predominantly the northeastern and upper midwestern United States, B. mayonii has been described in the upper midwestern United States. Lyme disease has both acute and chronic clinical patterns, and the liver may be involved in both. Hepatomegaly and abnormal LFTs, associated with portal tract inflammation on biopsy, are noted in the acute disease. Recurrent Lyme disease may cause a more marked hepatitis, with ballooned hepatocytes, mitotic activity, small-droplet macrovesicular steatosis, Kupffer cell hyperplasia and sinusoidal infiltration by lymphocytes and neutrophils. On Warthin–Starry or Dieterle silver stains, spirochaetes can be seen in the sinusoids and in liver cells. ^,