Why Does Bird Flu Not Cause a Major Outbreak in Humans?

Have you ever wondered why bird flu, although really bad for birds, is not as much an issue in humans?  Recent research provides us evidence of what is going on.  We'll attempt to summarize.

First, flu viruses are designated by two surface proteins H and N.
H - hemagglutinin, which enables the virus to infect human and animal cells where it can multiply,
N - neuraminidase, which helps the virus’s offspring to extract themselves from the infected cell.

So the virus enters the host cell, has the host replicate virus RNA which is used to make new viruses, and the high number of newly minted viruses explode out of the cell.  A person becomes sick as they fight off the viruses.  Worst case is when a person encounters new variants of  virus, that have different proteins including H and N, as would be the case with people getting a bird flu variant.  In this case, it takes the body longer to react to novel proteins of the variant, and the body has less defense system in place to fight the new virus.  The body reacts violently to counter the new virus, and it is this, the body's own defense system, that can be damaging (high fever, excessive phlegm, etc).

What this study found was that although the bird flu virus can infect a person, it does not replicate (make new virs) easily and thus does not spread easily.  The reason - the bird virus when in the human, does not produce a sufficient quantity of a protein, designated M1, responsible for getting the RNA out of the nucleus to begin making the new viruses in the cytoplasm of the host cell.   In humans, the bird viral RNA is spliced differently, making a protein called M2.

“Alternative splicing regulates which proteins are ultimately made from a single gene, because many genes code for more than one protein. When human cells are attacked by bird flu, this element ensures that more M2 rather than M1 protein is produced.”

May there be other factros? Sure.

 “How pathogenic an avian flu virus is and whether or not it has pandemic potential depends, of course, on many factors,” says Selbach. “A study on cell cultures cannot cover all these factors. Nevertheless, it might be useful in future to include an analysis of this RNA segment in the risk assessment of avian influenza viruses.”

https://www.mdc-berlin.de/news/press/what-blocks-bird-flu-human-cells
What blocks bird flu in human cells? 

CDC MMWR - Pet Rats Source of Seoul Virus (a Type of Hantavirus) - 2017

Considering a new pet rat?  Well, as part of the assessment, you may need to consider Seoul virus.  A report in MMWR reviews a 2017 outbreak of Seoul virus that had been linked to pet Norway rats.  In addition to two individuals who became ill and 183 who were serum positive,   "the investigation identified 31 facilities in 11 states with human and/or rat Seoul virus infections; six facilities also reported exchanging rats with Canadian ratteries."

Seoul virus is a type of hantavirus that causes symptoms ranging from mild influenza-like illness to severe disease with kidney failure and even death.  Norway rats are an asymptomatic carriers for the virus and transmit this virus to humans through contact with contaminated rat urine or droppings, or inhalation of virus particles in dust from contaminated bedding.  This is the first known case of pet rats being the source for human infection.

Norway rats, also known as brown rats, are considered a pest for food operations and can be the source of a number of different pathogens.  With a high birth rate and a diet that can consist of most anything, rat issues in a food facility can be an issue, being very difficult to eradicate once the rodents become established.  So the thought of owning a rat, is difficult for many..  And now, if this Seoul virus is not enough to make you think twice, just have to watch Willard.

CDC MMWR
https://www.cdc.gov/mmwr/volumes/67/wr/mm6704a5.htm?s_cid=mm6704a5_e
Outbreak of Seoul Virus Among Rats and Rat Owners — United States and Canada, 2017

Concern for Zika Virus - Mosquito transmitted disease of South and Central America

The Zika virus is a growing concern as it spreads throughout South and Central America as well as the Pacific Islands.  The mosquito is the primary vector.  While for most people, the symptoms of the viral infection are mild , there is a concern for pregnant women who become infected in that it may lead to microcephaly, a rare neurological condition in which an infant's head is significantly smaller which is associated with incomplete brain development.  Yikes.  (But this has not yet been totally proven.)

Cases of infection in the US have been seen in those who have traveled to areas where the virus is present.

Damn mosquitos...West Nile Virus was bad enough, now we got something else to worry about.  Mosquitos also carry other diseases including Chikungunya, dengue, yellow fever and malaria.

 

CDC Website

Zika Virus

http://www.cdc.gov/zika/index.html/

 

Zika virus is spread to people through mosquito bites. The most common symptoms of Zika virus disease are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting from several days to a week. Severe disease requiring hospitalization is uncommon.

 

Outbreaks of Zika have occurred in areas of Africa, Southeast Asia, the Pacific Islands, and the Americas. Because the Aedes species mosquitoes that spread Zika virus are found throughout the world, it is likely that outbreaks will spread to new countries. In December 2015, Puerto Rico reported its first confirmed Zika virus case. Locally transmitted Zika has not been reported elsewhere in the United States, but cases of Zika have been reported in returning travelers.

As US Poultry Industry Braces for the Potential of Avian Flu, H5N2, People Not at Risk

Avian influenza has been found in wild birds on the US border.  USDA has not found it in in US poultry, but the strains H5N2 and H5N8 have been found in Canadian and European flocks.  While these strains are highly pathogenic to birds, they are not considered a risk to people.
 
Migratory birds such as ducks are a risk factor for spreading the virus to the US poultry population.  Once infected, the flock is often culled to eliminate further risk of spreading the virus.

Just this past year, the pork industry suffered the fate of the PED virus, or Porcine epidemic diarrhea virus.  PEDV causes severe diarrhea in pigs and has a high lethality in piglets, but poses no risk to other animals or humans.   PED and Influenza are different types of viruses. PED is from the Coronaviridae family of enveloped, positive-stranded RNA viruses.  Influenza is an Orthomyxovirus.

CIDRAP
H5N2, H5N8 avian flu viruses surface in US
Robert Roos | News Editor | CIDRAP News
http://www.cidrap.umn.edu/news-perspective/2014/12/h5n2-h5n8-avian-flu-viruses-surface-us
Dec 16, 2014

US authorities today reported finding wild birds in Washington state infected with two different highly pathogenic avian influenza (HPAI) viruses, H5N2 and H5N8, raising questions about possible connections with recent H5N2 outbreaks across the border in Canada and with an Asian H5N8 strain that is now hitting European poultry farms.

In reports to the World Organization for Animal Health (OIE), the US Department of Agriculture (USDA) said H5N2 was found in a wild pintail duck, while H5N8 was found in a captive wild gyrfalcon that was fed on hunter-killed birds. Both birds were in Whatcom County, Washington, which borders the Abbotsford area of British Columbia, the site of recent H5N2 outbreaks in poultry.

Ebola virus - A Short Primer on Virus Survival and Disinfection

Here is a short primer on Ebola - condensed from information from the CDC website - focusing on disinfection and survival in the environment.
 
Survival in the Environment
 
According to the CDC, under ideal conditions where there is organic material (such as blood), the Ebola virus was show to survive up to 6 days in the environment.  But these viruses are susceptible to drying, UV and disinfectants.  (I is important to point out that there have been limited studies.)
 
That said, without organic material, it will die off quickly, so it is not likely to be present on doorknobs and light switches or other items that people simply touch (without blood or other organic residue).

How does this compare to Norovirus which can survive in the environment for weeks to months?  There are two categories of viruses - non-enveloped and enveloped.  All viruses are comprised of by genetic material within a protein structure or capsid....but enveloped viruses also have a lipid envelope surrounding that protein capsid while the non-enveloped virus do not.  Ebola is an enveloped virus, and that outer lipid layer, so important for attachment and entry to the cell, is more subject to environmental conditions.  Norovirus, a non-enveloped virus, is more resistant.

 

Disinfection

 
According to the CDC, Use a U.S. Environmental Protection Agency (EPA)-registered hospital disinfectant with a label claim for a non-enveloped virus (e.g., norovirus, rotavirus, adenovirus, poliovirus) to disinfect environmental surfaces in rooms of patients with suspected or confirmed Ebola virus infection. Although there are no products with specific label claims against the Ebola virus, enveloped viruses such as Ebola are susceptible to a broad range of hospital disinfectants used to disinfect hard, non-porous surfaces.
 
Basically, if it is good against the more hardy viruses like Norovirus, it will be fine against Ebola.

Transmission

 

From the CDC Website (below)

When an infection does occur in humans, the virus can be spread in several ways to others. Ebola is spread through direct contact (through broken skin or mucous membranes in, for example, the eyes, nose, or mouth) with

• blood or body fluids (including but not limited to urine, saliva, sweat, feces, vomit, breast milk, and semen) of a person who is sick with Ebola 
• objects (like needles and syringes) that have been contaminated with the virus
• infected animals
• Ebola is not spread through the air or by water, or in general, by food. However, in Africa, Ebola may be spread as a result of handling bushmeat (wild animals hunted for food) and contact with infected bats. There is no evidence that mosquitos or other insects can transmit Ebola virus. Only mammals (for example, humans, bats, monkeys, and apes) have shown the ability to become infected with and spread Ebola virus.
     

Symptoms 

• Fever (greater than 38.6°C or 101.5°F)
• Severe headache
• Muscle pain
• Weakness
• Diarrhea
• Vomiting
• Abdominal (stomach) pain
• Unexplained hemorrhage (bleeding or bruising)

 

Symptoms may appear anywhere from 2 to 21 days after exposure to Ebola, but the average is 8 to 10 days.

 

Recovery from Ebola depends on good supportive clinical care and the patient’s immune response. People who recover from Ebola infection develop antibodies that last for at least 10 yrs