BLOOD BORNE VIRUSES

Types:

A. Hepatitis B virus (HBV).

B. Hepatitis C virus (HCV).

C. Cytomegalovirus (CMV).

D. Human immunodeficiency virus (HIV).

E. Parvovirus B19.

In the health care setting, blood-borne pathogen transmission occurs predominantly by percutaneous or mucosal exposure of workers to the blood or body fluids of infected patients. Occupational exposures that may result in HIV, HBV, or HCV transmission include needlestick and other sharps injuries; direct inoculation of virus into cutaneous scratches, skin lesions, abrasions, or burns; and inoculation of virus onto mucosal surfaces of the eyes, nose, or mouth through accidental splashes. HIV, HBV, and HCV do not spontaneously penetrate intact skin, and airborne transmission of these viruses does not occur.

HBV, HCV and HIV have been associated with nosocomial infections, with transmission from patient to patient, from patients to health care workers and vice versa. Transmission of these viruses depends on transfer of blood, other body fluids, tissue from infected to uninfected individual and instruments contamination. Reduction of risks of transmission from patients to health care workers and vice versa needs number of important guidelines.

A. Hepatitis B virus (HBV):

HBV is a member of the Hepadnaviridae family. All appear after negative staining of electron microscope (EM) as double shelled particles. The surface of the virions consists of several hundred (possibly 240 subunits) comprising three different membranes- spanning polypeptides termed large and middle and small surface proteins. The HBV genome consist of a circular, partially double stranded DNA .

In the unvaccinated health care worker, the rate of transmission of the virus after percutaneous exposure to HBVe antigen (HBe Ag) positive blood may be higher than 30%. In U.S. HBV infection were less in vaccinated surgeons and other health care workers 4-5 times less than others. Staffs who are carriers of HBV have been shown to present a risk of transmission to their patients during the course of surgical or dental procedures. In the U.K. from 1975-1990, 12 outbreaks of HBV infection including 95 patients were associated with an infected health care worker as the source of outbreak .

Control of spread: Routine HBV immunization and monitoring of immune status ensure that health care workers are protected against the risks of HBV transmission. Non responders to the vaccine are offered hepatitis B-specific immunoglobulin following exposure to a known HBV surface antigen (HBs Ag)-positive

In U.K., guidelines recommend exclusion of HBeAg positive health care workers from participating in invasive procedures that pose a risk that injury to the worker may result in exposure of the patient's open tissue to the blood of the worker

B.Hepatitis C virus (HCV):

Knowledge of the length, nucleic acid composition and genome organization of HCV has led to its classification in the Flaviviridae family. HCV is single stranded RNA. HCV forms virus like particles of diameter 55-65 nm with 6 nm spikelike projections that may correspond to the envelope glycoproteins on the virion surface

There is documented risk of nosocomial transmission of HCV from patients to health care workers. The risk of infection from a single percutaneous injury involving HCV-positive blood is usually estimated to be approximately 3%. The presence of HCV RNA in the blood of patient is associated with greater risk of transmission to health care worker than if the individual is RNA negative

HCV infection has been reported in 5 patients undergoing minor surgery in a clinic in Australia. The mode of transmission is unknown, but may be either the reuse of a needle or syringe or contaminations of anesthetic equipment are the likely routes

During the investigation of suspected nosocomial transmission of HCV, molecular genetic techniques, including genotyping by restriction fragment length polymorphism analysis and genetic sequencing, assist in confirming the likelihood of a transmission event. No guidelines have been issued from the U.K. Health Departments to date, but health care workers who are shown to have transmitted the virus during surgical procedures are advised to cease participating in invasive procedures

C. Cytomegalovirus (CMV):

CMV spread by direct contact with body fluids, including vaginal secretions, semen, saliva and whole blood. Primary infection is usually asymptomatic, although some individuals may develop a glandular fever-like illness. Asymptomatic reactivation is common and facilitates transmission. Severe disease in immunocompromised patients e.g. BMT recipients can result from both primary infection and reactivation of latent virus. In immunocompromised patients severe primary infection or reactivation which produce variety of clinical syndromes including pneumonia, enteritis, encephalitis, chorioretinitis, hepatitis, cholongitis, cystitis, nephritis, adrenalitis and marrow suppression

Although there is concern that CMV may be transmitted nosocomially, there is little evidence to support this. Studies of hospital pediatric nurses caring for children excreting CMV showed that they were not more likely to acquire CMV than women of a similar age working in other occupations. Similarly, restriction enzyme analysis of isolates has failed to confirm cross-infection when a member of the staff has been exposed to CMV and subsequently acquired the virus

Although transmission between children has been reported in the hospital setting, it is likely that this horizontal transmission is due to close contact between the children rather than from a breakdown in infection control procedures. Although there is little evidence to suggest that CMV is transmitted in hospitals, basic precautions (gloves and aprons or gowns) should be employed when handling body fluids or contaminated linens or diapers

D.Human immunodeficiency virus (HIV):

The Retroviridae family includes HIV type 1 and 2. Retroviruses are distinguished by their ability to reverse transcribte their RNA to DNA by using the enzyme reverse transcriptase. DNA is then integrated into host cell chromosome by viral enzyme integrase. All retroviruses contain at least three major genes that encode the main virion structural components which are each synthesized as three polyproteins that produce the inner virion interior, the viral enzymes, or the glycoproteins of the virion envelope

The result of published by Centers of disease control (CDC) in Atlanta, provided evidence of factors that may enhance the transmission. Three of these factors are deep injury, visible blood on the device and inoculation with needle previously used in blood vessel. These factors are likely to have resulted in a larger transfer of blood to the recipient than would occur in less severe injuries. Patient to patient transmission of HIV has resulted from deficiencies in technique and/or decontamination procedures. Inadvertent reuse of a syringe and needle previously used for nuclear medicine investigations on HIV-positive patient transmitted infection to another patient

In the U.K., guidelines issued by the health department in 1994 recommended exclusion of all HIV-positive health care workers from invasive procedures (U.K. Health Departments, 1994). The principals of controlling nosocomial infection with HIV are similar to those applied to other blood-borne viruses. Evidence of a protective effect of an antiretroviral drug used for post exposure prophylaxis, together with data from animal studies and evidence of the value of zidovudine in preventing mother- to – baby transmission of HIV, supports the continued recommendation for post-exposure prophylaxis for health care workers exposed to HIV positive material

F. Parvovirus B19 (PV-B19):

PV from the "Latin: parvus" meaning small, non enveloped, ichosahedral protein virions. Some member of this family are major pathogens of insects and domestic animals but only one human PV-B19, has so far been identified as a human pathogen and is a causative agent of fifth disease

PV-B19 is a single-stranded DNA virus with a predilection for infecting rapidly dividing cell lines, such as bone marrow erythroid progenitor cells. People with defective cell-mediated immunity (e.g., severe combined immunodeficiency syndrome; acquired immunodeficiency syndrome; and patients receiving immunosuppressive therapy, i.e., post organ transplant) can develop pure red cell aplasia, in which suppression of erythroid precursors is permanent. Identification of parvovirus inclusions in marrow biopsies and subsequent confirmation of infection by in situ hybridization is important in the assessment of anemia in immunodeficient patients

PV-B19 is associated with erythema infuntosum (slapped cheek syndrome) in children, arthralgia and arthritis in adults, hydrops fetalis, transient aplastic crises in patients with hemaglobinopathies, and chronic anemia in immunocompromised patients. Typical infection results in biphasic illness, initial viremic phase occurs 5 days after exposure, during it the host is infectious to others, about a week later, the immunological phenomenon, rash and arthralgia, develop, and at this stage IgM is detected in serum of most infected individuals. Life long immunity develops in immunocompetent host, but chronic or recurrent anemia can occur in immunocompromised

Transmission is though to occur following close contact during the period of maximum infectivity (7 days before the appearance of rash) via large droplets or fomits. People with aplastic crises are infectious up to 1 week after the onset of symptoms, and those with chronic infection may remain infectious for prolonged periods. Environmental contamination also occurs, particularly following the birth of an infected infant. Attack rates between 0 and 30% have been reported in susceptible hospital staff

Because parenteral transmission of PV-B19 has been demonstrated via the transfusion of blood products from blood donated during the viremic stage of PV-B19 infection, screened blood should be considered, particularly for patients with sickle cell disease and other congenital anomalies, immunocompromised hosts, and women during pregnancy

The U.S. CDC does not recommend any restrictions for personal exposed to PV-B19 even if they are pregnant. This may be because a case is usually identified when the rash appears and the patient is no longer infectious. In U.K., respiratory precautions and hand washing are recommended for contacts with a patient with suspected or confirmed PV-B19 infection. Only those members of staff or patients who are immunocompromised or pregnant ( < 20 weeks ) who have had significant contact with the index case during the period of maximum infectivity ( 7 days before onset of the rash) need to be followed up. A significant contact is defined, as one who is in the same room for >15 min or who has had face to face contact

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