Thursday, August 11, 2011



A. Marburg and Ebola viruses.

B. Lassa fever virus.

C. Congo Crimean hemorrhagic fever.

A. Ebola and Marburg viruses:

The family Filoviridae harbors two genera, Marburg virus and Ebola virus. These viruses have non segmented negative strand RNA which is surrounded by a lipid envelop (Van Regenmortel et al., 2000). The genus Ebola virus however can be subdivided to 4 species: CÔte d´ Ivoire, Reston, Sudan, Zaire (Feldmann et al., 2004).

Factors identified as important in transmission included direct contact with an infected person during the symptomatic phase, contact with infected body fluids, blood, stool, vomitus and urine was also identified as important factors (Dowell et al., 1999). Indirect contacts following percutaneous exposures and laboratory accidents are also important in the hospital setting. The role of aerosol transmission is still not clear. While there is experimental evidence to support droplet transmission in rhesus monkeys, there is no clear evidence of its importance in human populations. Its potential importance should not be underestimated; however the relative risk may depend on the strain of the virus (Johnson et al., 1995).

Marburg virus was the first member of this family to appear in Germany in 1967. Thirty-one cases occurred in laboratory workers handling infected African green monkeys that had been imported to provide kidney cells to produce polio vaccine, secondary transmissions to hospital staff and family members had occurred. The significant mortality 23% and a general lack of knowledge regarding the life cycle and natural hosts of the virus resulted in the implementation of strict quarantine procedures for monkeys to prevent a recurrence (De Marcus et al., 1999).

In May 1999, an outbreak of Marburg disease was confirmed in the Democratic Republic of Conge (DRC). Although the natural reservoir is unknown, contact with infected monkeys is likely to be important. Person-to-person transmission is most likely to follow contact with infected blood; however, aerosol transmission has not been discounted, and sexual intercourse in the convalescent phase of the infection has resulted in a secondary case (WHO, 1999).

Ebola virus was identified in 1970 as the causative agent of 2 simultaneous outbreaks of hemorrhagic fever in the DRC and Sudan with mortality rate 88% and 50% respectively. In the Madiri hospital in the Sudan, 76 of 230 medical staff became infected, and 41 died. Secondary transmission was linked to the reuse of unsterelized needles and direct contact with body fluids (Rollin et al., 1999).

The index case was identified as a charcoal worker who died from hemorrhagic illness 7 days after his admission to hospital. Three members of his family and 10 secondary contacts died. A nosocomial outbreak among theatre staff was linked to a laparotomy performed on an infected laboratory worker presumed to have a perforated viscus. International scientific and medical teams were dispatched to implement infection control measures and monitor the outbreak. Adequate sanitation, safe disposal of sharps was implemented and quarantine facility was also established. These measures terminated further nosocomial transmission (Bwaka et al., 1999).

B. Lassa fever virus:

The first outbreak of Lassa fever occurred in 1969 in a small hospital in Lassa, in northern Nigeria. The first case was a nurse who died about 14 days after the onset of her symptoms. Two further nurses who cared for her also contracted the infection; one died, and the other was repatriated to the U.S. and eventually recovered after a prolonged illness. Two laboratory workers also became ill; one had handled infected tissue cultures and the other was based in another laboratory in the same building. Over the years, at least 12 patients have contracted Lassa fever and have been airlifted to Europe or the U.S. Despite a range of containment levels used, there has not been any serological evidence of secondary cases in over 200 apparently healthy contacts (Cooper et al., 1982).

The most recent imported case in the U.K. was a British aid worker based in Daru, eastern Sierra Leone. He became unwell on 21 February 2000 and was transferred to London on 6 March. Following the development of hemorrhagic complications, he was transferred to the high-security facility at Coppetts Wood Hospital in London, where he subsequently died. Person-to-person transfer results from contact with infected body fluids or following accidental exposure to blood via contaminated sharps. Intimate contact may also result in transmission; this may be a problem, as viral excretion may continue for a few months post recovery (Aitken and Jeffries, 2001).

C. Congo Crimean hemorrhagic fever:

This virus has a wide distribution and has been found in Russia, the central Asian republics, Dubai, Iraq, South Africa, Pakistan, Greece, Albania, Turkey, Afghanistan, and India. Geographic variation in virulence has been observed, with more severe disease following infection with Asian than with African strains. Natural infection results from a tick bite, but person-to-person transmission can occur following contact with infected body fluids. Secondary cases have also occurred following exposure to cases requiring resuscitation ( Suleiman et al., 1980).

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