A Practical Guide to Clinical Virology Second Edition - part 7 pdf

Degre´ Hepatitis A is a viral infection resulting in an acute necroinflammatory disease of the liver.. LABORATORY DIAGNOSIS The clinical virological diagnosis is made by demonstrating the

itself, HHV-6-induced reactivation of other infectious agents such as CMV, orsome other event for which HHV-6 reactivation is merely a marker isresponsible for the observed disease manifestations Fever, bone marrowsuppression, hepatitis, pneumonitis, encephalitis, graft or organ rejection, and

an increase in infections from CMV and fungi have been associated withHHV-6

THE VIRUS

HHV-6 is the sixth of eight described human herpesviruses Like the othermembers of the group, it has an electron-dense core composed of double-stranded DNA (160–170 kbp long) surrounded by nucleocapsid in the shape of

an icosahedron A tegument surrounds the capsid, and a trilaminar membranesurrounds the entire structure The nucleocapsid is 90–110 nm in diameter, andthe mature virion ranges from 160 to 200 nm in diameter The genome ofHHV-6 is most closely related to HHV-7; of all other herpesviruses these twosimilar viruses are most closely related to CMV Two variants of the virus havebeen described, HHV-6A and HHV-6B Although both utilize the ubiquitoushuman CD46 as a receptor, there are likely to be other factors involved inattachment or fusion as the two variants display different cellular tropisms intissue culture and in the host These tropisms may relate to observed diseaseassociations HHV-6B causes nearly all HHV-6-associated roseola and hasbeen implicated in most of the observed complications in immunosupressedhosts, while HHV-6A has only rarely been implicated in disease HHV-6Bgrows well in mature lymphocytes while HHV-6A replicates better in immaturelymphocytes

EPIDEMIOLOGY

HHV-6 is a ubiquitous virus which is found worldwide and appears to infectmost children by the age of two years The virus can be found in the saliva ofaround 70% of asymptomatic adults, closely matching the seroprevalence inthe adult population Transmission is thought to occur by direct contact withinfectious secretions passing from asymptomatic adults to seronegativechildren, typically from mother to child Virus can be recovered from saliva,genital secretions and brain at autopsy in asymptomatic adults Virus isgenerally only recovered from blood during viraemia such as at the height offever during primary infection (roseola) or during reactivation in immuno-compromised hosts, but can be detected in latent form with sensitivetechniques such as PCR

THERAPY AND PROPHYLAXIS

There is no specific antiviral therapy for roseola Supportive care such ashospitalization of infants for dehydration is sometimes necessary Ganciclovir170

has antiviral activity in vitro, and it has been suggested that severe illnessassociated with reactivation in immunosuppressed hosts be treated withganciclovir or foscarnet Clinical efficacy data are not available.

Prophylaxis is not available

LABORATORY DIAGNOSIS

Diagnosis of roseola is clinical HHV-6 can be detected by culture of peripheralblood mononuclear cells during primary infection or reactivation but is rarelyused due to its difficulty Laboratory diagnosis in immunosuppressed patients

by seroconversion or qualitative PCR is available commercially but is rarelyhelpful clinically due to the high rate of seropositivity (approaching 100% atage 2 years) and frequency of positive PCR in sites such as blood, saliva andbrain tissue Quantitative and real-time PCR techniques are currently foundonly in research laboratories and may prove more useful for delineating diseaseassociations by following serial values from blood

PREVENTING TRAVEL SICKNESS?

A Practical Guide to Clinical Virology Edited by L R Haaheim, J R Pattison and R J Whitley

Copyright  2002 John Wiley & Sons, Ltd ISBNs: 0-470-84429-9 (HB); 0-471-95097-1 (PB)

24 HEPATITIS A VIRUS

Hepatitis A has been called infectious hepatitis, epidemic hepatitis

and short incubation hepatitis

M Degre´

Hepatitis A is a viral infection resulting in an acute necroinflammatory disease

of the liver The clinical features are age-dependent, mostly mild or sub-clinical

in children, while in adults dominated by jaundice and general fatigue

TRANSMISSION/INCUBATION PERIOD/CLINICAL FEATURESVirus is excreted in the faeces mostly during the late phase of incubationperiod and to a lesser extent during the early phase of the disease It istransmitted via the faecal–oral route, through contaminated water andfood and direct contact, especially under poor hygienic conditions Theincubation period is approximately 4 weeks (2–6 weeks) and dependent

on the size of inoculum

SYMPTOMS AND SIGNS

Prodromal phase: Malaise, Weakness, Mild Fever, Nausea and

Vomiting, Anorexia, Headache, AbdominalDiscomfort

Icteric phase: Jaundice, Itching, Dark Urine, Pale Stools

The majority of young patients are symptomless or they have mildgeneral symptoms The prodromal phase that lasts 2–7 days is followed

by the icteric phase lasting usually 1–2 weeks, often longer in adults.Some patients show general fatigue for several weeks, or even months.Extrahepatic manifestations are uncommon

COMPLICATIONS

Fulminant hepatitis occurs in less than 1% of patients Relapsinghepatitis A and cholestatic forms have been described but are alsouncommon

THERAPY AND PROPHYLAXIS

There is no specific causal therapy available Normal immunoglobulinhas a protective effect when given before or shortly after exposure Bothinactivated and attenuated vaccines have been developed and areavailable

LABORATORY DIAGNOSIS

The clinical virological diagnosis is made by demonstrating the presence

of IgM antibodies in the early phase of clinical disease or by strating seroconversion Early infection can be diagnosed by the presence

demon-of IgG antibodies

174

Figure 24.1 HEPATITIS A VIRUS (ACUTE HEPATITIS A)

CLINICAL FEATURES

SYMPTOMS AND SIGNS

The incubation period is usually 4 weeks (2–6 weeks) The site of the primaryinfection is in the alimentary tract, although the sequence of events that beginswith entry via the gastrointestinal tract and eventually results in hepatitis is notwell understood A short prodromal or preicteric phase, varying from 2 to 7days, usually precedes the onset of jaundice The most prominent symptoms inthis phase are fever, headache, muscular and abdominal pain, anorexia,nausea, vomiting and sometimes arthralgia Hepatomegaly and leukopenia areoften present during this period In typical cases the urine becomes dark, andthe stools pale before appearance of yellow discoloration of the mucousmembranes and appearance of jaundice about 10 days after onset of thegeneral symptoms Fever and most of the general symptoms usually subsidewithin a few days of jaundice, but in severe cases both general and abdominalsymptoms may become further aggravated at this phase Jaundice is oftenaccompanied by itching and sometimes by urticarial or papular rashes Liver isusually enlarged and liver function tests are abnormal with highly elevatedlevels of serum alanine aminotransaminase (ALT) and serum aspartateaminotransaminase (AST)

Differential diagnosis It is not possible to differentiate between hepatitis A andacute hepatitis caused by other infectious agents, e.g hepatitis B, hepatitis C,hepatitis E, cytomegalovirus and EBV, by clinical examination or by liverbiopsy The history and epidemiological details are of great importance inreaching a presumptive diagnosis The precise aetiology must be confirmed bylaboratory tests

CLINICAL COURSE

Most infections run an asymptomatic course, especially in children The disease

is usually mild and of short duration in children and young adults Clinicalsymptoms are likely to disappear after 10–14 days In adults the symptoms areoften more severe and long-lasting, e.g 4–5 weeks The liver function testsrapidly return to normal when clinical symptoms disappear, but in some casessymptoms may persist for several months, during which time the patient feelstired and often depressed Hepatitis A virus does not cause chronic hepatitis,although long-lasting excretion of virus has been reported

COMPLICATIONS

Fulminant hepatitis with a clinical picture of acute yellow atrophy is anuncommon but serious (lethality 0.3%) complication with high mortality.Extrahepatic complications like myocarditis and arthritis are also rare

THE VIRUS

Hepatitis A virus (HAV) is a member of the picornavirus family It consists of

a naked icosahedral particle of 27 nm diameter The genome is a stranded RNA, linear, positive-sense, 7.48 kbp, MW 2.25 million daltons Itcodes for a polyprotein, which is cleaved into four major structural proteinsVP1–4 The surface proteins VP1–3 are major antibody-binding sites It wasfirst provisionally classified as enterovirus 72, but subsequently it has beenshown that both nucleotide and aminoacid sequences are dissimilar from theother enteroviruses, and it is now classified as its own genus, hepatovirus.Although minor strain variations occur, there is only one serological type, but

single-we can differentiate betsingle-ween four types Hepatitis A virus is stable totreatment with organic solvents, ether andacid and is more heat-resistant than otherpicornaviruses; it withstands 60 8C for 1hour The virus is difficult to adopt to cellcultures and replicates very slowly, usuallywithout cytopathogenic effect In vivo HAVprimarily multiplies in Peyer’s patches inthe intestinal tract and later in hepatocytesand Kupffer cells Viral antigen can bedemonstrated by immunofluorescence inliver biopsies The liver damage is probablypartly a direct result of the viral cyto-pathogenic effect, but T-cell-mediatedimmunological mechanisms seem to beimportant HAV can be transmitted tochimpanzees and marmoset monkeys

In industrialized countries most people are susceptible to infection andtravellers to developing countries thus carry the risk of contracting theinfection The occurrence of hepatitis A in north-west European countries and

in North America has been much reduced during the last decades Antibodies176

to HAV have been found in 80–90% of individuals born before World War II,but only 5–20%, or even less, of those under 20 years of age.

THERAPY AND PROPHYLAXIS

There is no specific therapy Bed rest is traditional in the treatment of hepatitis

A and is recommended if the general situation indicates so, especially in elderlypatients and during pregnancy The preventive effect of immunoglobulin is welldocumented Administration of 0.02–0.06 ml/kg (2–5 ml) normal immuno-globulin before exposure gives 80–90% protection for a period of 4–6 months.Even after infection, given during the early part of the incubation period,immunoglobulin can prevent clinical disease, although virus may be present inthe intestines Immunoglobulin is recommended to people travelling toendemic areas A formalin-inactivated vaccine is now generally available.After two doses of vaccine almost 100% of individuals develop antibodies andare protected against infection An attenuated vaccine has also beenintroduced Spread of virus infection is to a large extent a function ofsocioeconomic standards and can be prevented by means of good hygiene.Infectivity of virus is destroyed by boiling for 15 minutes or at 60 8C for 30minutes Chlorine derivatives, formaldehyde and glutaraldehyde are alleffective in routinely employed concentrations, while phenols, ether andother organic solvents are not Isolation of the patients is not necessary asinfectivity in the icteric phase is usually insignificant

LABORATORY DIAGNOSIS

HAV is present in stools before the onset of clinical symptoms and can bedemonstrated by electron microscopy Isolation in cell cultures is difficult andnot practical for diagnostic use Detection of nucleic acid with PCR can beuseful both as an epidemiological tool and in environmental studies but it isnot indicated for clinical use Antibodies can be demonstrated from the onset

of the clinical symptoms Diagnosis of acute infection requires demonstration

of anti-HIV IgM antibodies or seroconversion IgM antibodies disappearabout 3–6 months after the onset of disease IgG antibodies on the other handpersist for life and indicate immunity against reinfection Antibodies aredemonstrated by means of EIA or RIA

RISKY BUSINESS

A Practical Guide to Clinical Virology Edited by L R Haaheim, J R Pattison and R J Whitley

Copyright  2002 John Wiley & Sons, Ltd ISBNs: 0-470-84429-9 (HB); 0-471-95097-1 (PB)

25 HEPATITIS B VIRUS

Previously called serum hepatitis, post-transfusion hepatitis

and inoculation hepatitis

G L Davis

Infection with the hepatitis B virus (HBV) can result in acute hepatitis,fulminant hepatitis, a chronic asymptomatic carrier state, chronic hepatitis,cirrhosis or hepatocellular carcinoma

TRANSMISSION/INCUBATION PERIOD/CLINICAL FEATURESHBV is present in blood and bodily secretions The virus is mostcommonly spread by sexual contact, but it can also be spread from mother

to child at birth, through contaminated needles and transfusion (extremelyrare) The incubation period averages 75 days (range 1–6 months)

SYMPTOMS AND SIGNS

Systemic: Fever, Fatigue, Malaise, Dyspepsia, Rash,

ArthralgiaLocal: Hepatomegaly, Pale Stools, Dark Urine, Jaundice

Acute infection is usually mild and anicteric; only about a third ofpatients are aware of the infection Complete recovery occurs in morethan 95% of adults, but is unusual (510%) if infection occurs in infancywhen most infections become chronic Chronic HBV infection maypresent in one of two ways Individuals infected early in life are tolerant

of the virus and often have an asymptomatic carrier state with normalliver tests Those infected later in life usually present with chronichepatitis and elevated liver enzymes The latter are more likely to havesymptoms and develop progressive liver damage at a faster rate

COMPLICATIONS

About one in six patients with acute hepatitis has serum sickness-likesymptoms of rash, fever and arthralgia Fulminant hepatitis is unusual(assumed to be 1 in 200) Chronic hepatitis leads to cirrhosis in morethan 20% of cases, and the risk of hepatocellular carcinoma is increasedabout 50-fold Polyarteritis nodosa, glomerulonephritis and papular

acrodermatitis (only in children) occur rarely in those with chronichepatitis.

THERAPY AND PROPHYLAXIS

Acute infection can be prevented by the HBV vaccine Infants born toHBV-infected mothers should also receive HBV immunoglobulin(HBIG), which is also recommended for postexposure prophylaxis.Interferon eliminates viral replication in 40–50% of treated patientsmostly Response is usually permanent Lamivudine and some newnucleoside analogues may be equally effective, though viral resistancemay emerge

LABORATORY DIAGNOSIS

In an acute infection the detection of HBsAg and IgM antibody to thenucleocapsid (HBc) is characteristic, followed by development ofconvalescent anti-HBs antibodies Chronic infection is indicated by thepresence of HBsAg and absence of IgM anti-HBc Viral replicationoccurs during the initial high replicative phase of infection and thesepatients are HBeAg and HBV-DNA (by a non-PCR method) positive.About 10% of patients annually will spontaneously develop into a lowreplication stage; becoming HBeAg and HBV-DNA (by a non-PCRmethod) negative and anti-HBe positive Loss of HBsAg is extremelyunusual in patients with chronic infection unless they have been treatedwith interferon

180

Figure 25.1 HEPATITIS B VIRUS (ACUTE HEPATITIS B)

CLINICAL FEATURES

SYMPTOMS AND SIGNS

The incubation period of HBV infection averages 75 days (1–6 months) Mostpatients have minimal or no symptoms during infection However, 15%present with fever, arthralgia and rash, and another 15–20% present with non-specific symptoms of malaise, anorexia and nausea About a quarter of patientswill become icteric Findings on physical examination are usually non-specificthough hepatomegaly may be noted in some cases

Differential diagnosis The symptoms of acute hepatitis are non-specific Similarsymptoms may be seen in other forms of viral or drug-induced hepatitis Inchildren and adolescents, EBV should be considered In older adults,cholecystitis, cholangitis and common bile duct obstruction become considera-tions The hepatocellular pattern of liver test abnormalities (elevated AST andALT with slight or no elevation of alkaline phosphatase) should lead to adiagnosis rather than biliary disease in most cases An ALT level higher than

1000 U/litre is seen only in viral hepatitis, drug-induced hepatitis and ischaemichepatic injury Serological diagnosis is required to confirm the HBV infection

CLINICAL COURSE

Serological markers of infection (HBsAg) appear in the blood early in theincubation period This is followed within a few weeks by evidence of viralreplication (HBeAg and HBV-DNA (by a non-PCR method)) These markersand liver enzymes reach their highest level at about the time of onset ofsymptoms, which abate within 2–3 weeks but may persist for months In themajority of patients (490%), HBsAg disappears from the blood as the liverenzymes normalize Convalescent antibody (anti-HBs) will develop in most ofthese patients Persistence of HBsAg and HBeAg for more than 10 weeksindicates that chronic infection is likely to evolve Chronic hepatitis persists foryears The initial phase is characterized by high levels of viral replication withdetectable HBeAg and HBV-DNA (by a non-PCR method) Patients areinfectious and at risk for progressive liver injury during this period Cirrhosisdevelops in 20–50% of cases About 10% of patients each year will have aspontaneous reduction in viral replication in which HBeAg and HBV-DNA(by a non-PCR method) become undetectable These individuals arecommonly no longer infectious and their liver disease becomes inactive.However, it is very unusual for patients with chronic HBV infection to clear theinfection and lose HBsAg unless they receive antiviral treatment

COMPLICATIONS

The major long-term risks of chronic HBV infection are cirrhosis with hepaticfailure and hepatocellular carcinoma Cirrhosis develops in 20–50% of cases

and is associated with a poor prognosis, particularly if HBeAg is present.Between 25 and 50% of cirrhotic patients will develop liver failure.Hepatocellular carcinoma occurs most frequently in cirrhotic patients whohave had long-standing liver disease The risk is increased 450-fold comparedwith the normal population Extrahepatic manifestation of infection such aspolyarteritis nodosa and glomerulonephritis are rare, but when present areoften more problematic than the hepatitis An increasingly common problem isthe development of viral variants The most common is the precore mutantwhich presents with active replication (HBV-DNA (by a non-PCR method)positive) but no HBeAg The patients behave like others with chronic hepatitis,but their course may be somewhat more aggressive.

in considerable excess compared with thevirion and may play a permissive role in viralpersistence However, HBsAg may be present

in blood when replication cannot be mented Therefore, the presence of HBsAGdoes not necessarily imply contagiousness.HBV replicates in hepatocytes and possibly

docu-in peripheral blood mononuclear cells Itsgenome is the smallest of all known animalDNA viruses The replicative process isunusual in several aspects; it has an efficientgenomic design of four overlapping open reading frames, it utilizes successivestrand synthesis and reverse transcription similar to retroviruses, and it hasboth glucocorticoid- and hepatocyte-specific enhancing elements Viralreplication can be documented by measuring HBeAg (a component of thecore gene product) or HBV-DNA (by a non-PCR method) in serum

EPIDEMIOLOGY

HBV infection is a formidable immense worldwide problem More than 200million people are chronically infected The prevalence is highly variable in theFar East, and in Mediterranean and Eastern European countries, whereas insub-Saharan Africa the endemic rates are highest, with as many as 20% of the182

Figure 25.2 HEPATITIS B

VIRUS AND HBsAg

PARTI-CLES Bar, 100 nm (Electron

micrograph courtesy of E

Kjeldsberg)

population being infected In North America and Western Europe the infection

is not common (0.1–0.2%) The major route of infection in high endemic areas

is perinatal In countries of low endemicity, the major routes of infection aresexual and shared needles amongst intravenous drug users The latter group isnotoriously difficult to target by vaccination However, universal or extensivevaccination may be the only practical means of achieving a significantreduction of HBV prevalence

THERAPY AND PROPHYLAXIS

HBV infection is a preventable disease Vaccination has been available since theearly 1980s, but compliance has been poor in low endemicity areas and the highcost has delayed widespread usage in high endemicity areas Postexposureprophylaxis with high titre hepatitis B immunoglobulin (HBIG) provides short-term passive protection but is only about 75% effective No specific treatment

is required for acute hepatitis B since most individuals will clear the infectionspontaneously Patients with chronic hepatitis should be evaluated fortreatment with alpha interferon Overall the likelihood of clearing the infectionwith interferon is 40–50%, and for patients with elevated ALT and a lowquantity of HBV-DNA (by a non-PCR method) the response is significant andusually permanent Many patients will even lose HBsAg over a period of 4–5years after responding to interferon HBV is quite sensitive to several newnucleoside analogies, but the effect of these drugs is usually transient unlessused for at least 12 months Drug resistant variants may appear, particularlyafter prolonged therapy

LABORATORY DIAGNOSIS

HBsAg is the most important serological marker for identifying infection It ispresent early in acute infection, disappears with resolution of infection andpersists in chronic infection IgM anti-HBc is essential for the diagnosis ofacute infection, but is also seen occasionally in very active chronic hepatitis.Anti-HBc antibodies develop and persist after all HBV infections The loss ofHBsAg and development of anti-HBc signals resolution of acute infection.Anti-HBs also occurs post vaccination, but anti-HBc will not be present in suchcases Chronic infection is manifested by persistent HBsAg Markers of viralreplication such as HBeAg and HBV-DNA (non-PCR method) are detectableduring the early high replication phase, but are not detectable during the laterquiescent low replication phase HBeAg is not a reliable marker of HBVreplication when a precore variant is responsible for the infection Such caseswill be HBeAg negative, anti-HBe positive, but HBV-DNA (by a non-PCRmethod) positive