Marburgviruses: An Update

Caterina M. Miraglia, DC, MLS(ASCP)

Disclosures

Lab Med. 2019;50(1):16-28. 

In This Article

Reservoir

MVD is a zoonosis (a disease that can be transferred from animals to humans or vice versa); in other words, the life cycle of viruses is maintained in animal host(s) and spills over accidentally into the human population.[3] Marburgviruses are endemic in Angola, Democratic Republic of Congo, Kenya, Uganda, and Zimbabwe.[22] The host reservoir was previously unknown, but the evidence was strong that bats were likely involved, due to the fact that most index cases were known to have visited caves or mines (Table 1).

In July 2007, MARV RNA was isolated from a Rousettus aegyptiacus bat (Egyptian fruit bat; Image 2) caught in Kitum Cave in Mount Elgon National Park, Kenya.[23] Ecological studies were conducted in Kitaka Mine in Uganda not long after the 2007 outbreak had begun there. During the investigations conducted in August 2007 and April 2008, researchers detected marburgviral RNA in R. aegyptiacus by quantitative real-time polymerase chain reaction (RT-qPCR) and detected immunoglobulin (Ig)G antibodies to marburgviruses. Also, for the first time, they were able to isolate live virus specimens from healthy R. aegyptiacus bats caught in the mine. Multiple genetic lineages of the virus were identified, and sequencing of virus from R. aegyptiacusrevealed identical or nearly identical sequences to those of the miners infected during the outbreak. The data collected during this study implicated R. aegyptiacus as a natural host reservoir of marburgviruses.[24]

Image 2.

Rousettus aegyptiacus, the host reservoir of marburgviruses; viral RNA isolated from a Rousettus aegyptiacus bat. Photo courtesy of www.nature-images.eu © Arthur Tiutenko.

The results of a recent study[25] have demonstrated that R. aegyptiacus is a natural reservoir of marburgviruses but not of ebolaviruses. It was unknown, however, how the bats acquired the viruses and whether arthropods played a role in transmitting the virus to them. Ornithodoros faini ticks feed on R. aegyptiacus, so 3125 O. faini ticks from Python Cave in Queen Elizabeth National Park in Uganda were collected and tested for marburgviral RNA using RT-qPCR. No RNA was detected in any of the ticks collected; therefore, it is unlikely that they are involved transmission of marburgviruses to R. aegyptiacus.[26]

Further studies to determine how the virus is transmitted and maintained in the R. aegyptiacus population have been conducted. Horizontal transmission occurred between laboratory–MARV-infected and uninfected R. aegyptiacus that had direct contact with one another in the same cage, as well as indirectly in cages beneath the cage of infected bats.[27] MARV RNA has been detected in various tissues, including the salivary glands, kidneys, bladder, large intestine, and blood, as well as the oral secretions, urine, and feces of infected R. aegyptiacus;[27–29] the virus was isolated from oral and rectal swabs of those infected bats.[28] This finding indicates that horizontal transmission to the reservoir occurs due to direct or indirect exposure to these fluids and that direct or indirect exposure could transmit the virus to other animals and humans.[27]

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