virology blog

About viruses and viral disease

flavivirus

Microbes After Hours: West Nile virus

by

This discussion of West Nile virus was recorded at the headquarters of the American Society for Microbiology during a “Microbes After Hours” event on May 6, 2013. The speakers are Dr. Lyle Petersen Lyle R. Petersen, M.D., M.P.H., director of the Division of Vector-Borne Diseases at CDC, and Dr. Roberta DeBiasi, MD, FIDSA, Associate Professor of Pediatrics at George Washington University School of Medicine, Acting Chief and Attending Physician in the Division of Pediatric Infectious Diseases at Children’s National Medical Center, and investigator at Children’s Research Institute in the Center for Translational Science in Washington, D.C.

MWV Episode 70 – Microbes After Hours – West Nile Virus from microbeworld on Vimeo.

A new rhabdovirus from a patient with hemorrhagic fever

by

Viral hemorrhagic fevers in AfricaHemorrhagic fevers are among the most graphic viral diseases, inspiring movies, novels, and a general fear of infection. They are characterized by an abrupt onset and a striking clinical course involving bleeding from the nose and mouth, vomiting with blood, and bloody diarrhea. The most famous hemorrhagic fevers are produced by infection with filoviruses like Ebola virus, but members of three other viral families – Arenaviridae, Bunyaviridae, and Flaviviridae – can also cause this syndrome. The isolation of a novel rhabdovirus from an African with hemorrhagic fever suggests that members of a fifth viral family can also cause this disease.

Three cases of hemorrhagic fever that occurred in the spring of 2009 were noteworthy because none of the typical viral suspects could be detected in one patient. Two were young (13, 15 year old) students in the village of Mangala, Bas-Congo province, Democratic Republic of Congo. They lived near each other and went to the same school. Both arrived at the local health center with typical symptoms of hemorrhagic fever, and both died 2-3 days later. The third case was a 32 year old male nurse at the health center who was involved in the care of the other two patients. He developed symptoms of hemorrhagic fever but recovered within a few days.

Deep sequence analysis of RNA extracted from the serum of patient #3 revealed the presence of a novel rhabdovirus, provisionally named Bas-Congo virus (BASV). Phylogenetic analyses reveal that BASV is substantially diverged from the two main human rhabdoviruses, rabies virus and Chandipura virus (ten of the 160 known species of rhabdoviruses have been isolated from humans). BASV is more related to viruses of the Tibrogargan group and the Ephemerovirus genus, which contain arthropod-borne viruses that infect cattle, but clusters separately in an independent branch of the phylogenetic tree.

Antibodies to BASV were detected in the serum of patient #3 and also in the serum of an asymptomatic nurse who had cared for this patient. However, no antibodies to this virus were found in 43 other serum samples from individuals with hemorrhagic fever of unknown origin. These samples came from individuals who lived in 9 of the 11 provinces of the DRC, including Bas-Congo. Nor were antiviral antibodies detected in plasma from 50 random blood donors in one DRC province.

Although the viral genome sequence was determined from RNA extracted from patient serum (where there were 1 million copies per ml of the viral RNA), the virus did not replicate in cell cultures from monkey, rabbit, and mosquito, or in suckling mice. These findings are in contrast to those obtained with a newly discovered coronavirus in humans. It is likely that the samples had not been kept sufficiently cold to maintain viral infectivity. It should be possible to recover virus from a cloned DNA copy of the viral genome.

These data suggest, but do not prove, that BASV caused hemorrhagic fever in the 3 patients. All three cases occurred in a 3 week period within the same small village. BASV nucleic acid and antibodies were detected in the third patient. Given that viruses of the closely related Tibrogargan group and the Ephemerovirus genus are transmitted to cattle by biting midges, it is possible that the initial infections were transmitted by such an arthropod vector. Human to human transmission of the virus could have taken place when the nurse was infected by one or both pediatric patients. However, it should be noted that infection with BASV was not confirmed in either of the first two cases as no clinical samples were available. Other etiologies for this outbreak of hemorrhagic fever should not be ruled out.

Rhabdoviruses are known to cause encephalitis, vesicular stomatitis, or flu-like illness in humans, not hemorrhagic fevers. But these viruses clearly have the potential to cause this disease: members of the Novirhabdovirus genus cause hemorrhagic septicemia in fish. As long as there are viruses to discover, any rules we make about them should be considered breakable.

G Gerard, JN Fair, D Lee, E Silkas, I Steffen, J Muyembe, T Sittler, N Veerarghavan, J Ruby, C Wang, M Makuwa, P Mulembakani, R Tesh, J Mazet, A Rimoin, T Taylor, B Schneider, G Simmons, E Delwart, N Wolfe, C Chiu, E Leroy. 2012. A novel rhabdovirus associated with acute hemorrhagic fever in central Africa. PLoS Pathogens  8.

TWiV 137: Look what the dog dragged in

by

dog_humanHosts: Vincent Racaniello, Alan Dove, Rich Condit, Dickson Despommier, Amit Kapoor, and Ian Lipkin

The TWiV team speaks with Amit Kapoor and Ian Lipkin about how they discovered canine hepacivirus, and its implications for the origin and evolution of hepatitis C virus.

[powerpress url=”http://traffic.libsyn.com/twiv/TWiV137.mp3″]

Click the arrow above to play, or right-click to download TWiV #137 (69 MB .mp3, 96 minutes).

Subscribe to TWiV (free) in iTunes , at the Zune Marketplace, by the RSS feed, by email, or listen on your mobile device with the Microbeworld app.

Links for this episode:

Weekly Science Picks

Alan – What do marine mammals eat? (YouTube)
Rich – NIH rocket boys
Dickson – Cytomegalovirus needs an antiviral protein (Science)
 Vincent – All pdfs free at National Academy of Science Press

Listener Pick of the Week

Adriana and Ye Jung  – The man who was cured of AIDS (article one and two)

Send your virology questions and comments (email or mp3 file) to twiv@microbe.tv, or call them in to 908-312-0760. You can also post articles that you would like us to discuss at microbeworld.org and tag them with twiv.

The press concludes that arboviruses can be sexually transmitted

by

zika virus distributionWhat would you conclude if you read the following headlines: Man sexually transmits insect-borne disease to wife (Fox News); Zika virus: First insect borne STD? (HuffPo); Scientist gives insect-borne disease to wife during sex (New York Magazine), and A scientist contracts a mosquito-borne virus and gives it to his wife as std (Time). What would be your impression if you read the journal article on which these headlines are based, which does not conclude that the infection was transmitted sexually?

Zika virus was isolated in 1947 from a monkey in Uganda, and subsequently shown to be transmitted by mosquitoes. Zika is classified as a flavivirus, along with well-known human pathogens such as yellow fever virus, dengue virus, and West Nile virus. Infection of humans with Zika virus leads to headache, fever, malaise, myalgia, and formation of  a maculopapular rash on the face, neck, trunk, and arms. The virus is found mainly in African and parts of Asia (see map).

The case that has precipitated incorrect reporting began with two American scientists working in Senegal in 2008, where they were sampling mosquitoes. Between 6-9 days after returning to their homes in Colorado, they developed a variety of symptoms of infection including fatigue, headache, chills, arthralgia, and a maculopapular rash. The wife of one patient, who had not traveled to Africa, developed similar symptoms three days after her husband. Analysis of paired acute and convalescent sera from all three patients revealed antibodies against Zika virus. The two individuals who had traveled to Africa also had antibodies to yellow fever virus, a consequence of immunization with the vaccine.

Here is what the authors conclude from these data:

Evidence suggests that patients 1 and 2 were infected with ZIKV, probably in southeastern Senegal, by bites from infected mosquitoes…Circumstantial evidence suggests direct person-to-person, possibly sexual, transmission of the virus (italics are mine).

The authors do not conclude that transmission from husband to wife was via sexual activity – they suggest it as a possiblity. The authors know that one cannot prove sexual transmission from such a small study. They go on to write:

If sexual transmission could be verified in subsequent studies, this would have major implications toward the epidemiology of ZIKV and possibly other arthropod-borne flaviviruses.

What other ways might the infection have been transmitted from husband to wife? Virus is likely present in the skin of infected individuals, as a rash is a prominent feature. It is possible that virus was transmitted via cuts or abrasions in the skin. Another possibility is that virus is present in saliva or other body fluids, and is transmitted to others by close contact. The authors don’t believe this to be the case because they write that ‘illness did not develop in the 4 children of patients 1 and 3‘. However physical contact between husband and wife is substantially different from the contact between parents and children, which could have a major role in determining virus transmission.

Here is another way to put this puzzling state of affairs into context. In 2009 a group of scientists published a paper in Science indicating that they had found a retrovirus, XMRV, in the blood of 68 of 101 patients with chronic fatigue syndrome. To this day whether or not XMRV causes chronic fatigue syndrome is still being debated, despite studies in hundreds of individuals. In light of this situation, why does the press conclude from a study of three individuals that Zika virus can be sexually transmitted? Could it be that the journalists didn’t read the journal article (poor excuse – it’s quite short), or if they did, they decided that the conclusions were not sufficiently interesting? Or maybe the sex angle – always a good way to get the reader’s attention – was too good to resist, never mind that it might not be correct. Either way, the public is being misinformed about science – again.

Update: There has been discussion in the comments section that the news articles I cite don’t do such a bad job in presenting the science, and it’s the headlines that are the main problem. I don’t agree with that conclusion about the articles – in my opinion they don’t accurately portray the content of the paper. My journalist friends tell me that the headline writers often take liberty with conclusions; but I don’t see why we should use that as an excuse to forgive inaccurate headlines. How many people never get past the headlines? Both the headline and the article need to be consistent and they need to accurately represent the science.

Foy, B.D., Kobylinski, K.C., Foy, J.L.C., Blitvich, B.J., da Rosa, A.T., Haddow, A.D., Lanciotti, R.S., & Tesh, R.B. (2011). Probable non–vector-borne transmission of Zika virus, Colorado, USA. Emerging Infectious Diseases : 10.3201/eid1705.101939

Hayes, E. (2009). Zika Virus Outside Africa Emerging Infectious Diseases, 1347-1350 DOI: 10.3201/eid1509.090442

TWiV 90: Guano happens

by

Hosts: Vincent Racaniello, Alan Dove, Rich Condit, and Eric F. Donaldson

On episode #90 of the podcast This Week in Virology, Vincent, Alan, Rich and Eric discuss identification of viruses in Northeastern American bats, vaccinia virus infection after sexual contact with a military vaccinee, and identification of a new flavivirus from an Old World bat in Bangladesh.

[powerpress url=”http://traffic.libsyn.com/twiv/TWiV090.mp3″]

Click the arrow above to play, or right-click to download TWiV #90 (64 MB .mp3, 89 minutes)

Subscribe to TWiV (free) in iTunes , at the Zune Marketplace, by the RSS feed, or by email, or listen on your mobile device with Stitcher Radio.

Links for this episode:

Weekly Science Picks

Eric – Year of Darwin by Sean Carroll
Rich – March of the Penguins
Alan – Standing-height desks
Vincent – DengueWatch (thanks Richard!)

Send your virology questions and comments (email or mp3 file) to twiv@microbe.tv or leave voicemail at Skype: twivpodcast. You can also post articles that you would like us to discuss at microbeworld.org and tag them with twiv.