Don’t mistake this for sugar!
I chose to research the infectious zoonotic disease Anthrax (Bacillus anthracis). I think it’s interesting because it comes in many forms, all of which are potentially fatal if not treated and can be found virtually everywhere. Although not as common in the U.S. it’s still prevalent in many areas throughout the world and everyone should be educated on what to do if they come into contact with the bacteria. 
First, it feels incredibly cool to say I’ve been to the CDC. Awesome. Second, I kind of have mixed feelings about it. Let me explain. ^-^ So I understand that they could only show us so much, but for the CDC I figured the labs would look a lot more high tech. I feel like they looked like the regular labs I have access to at the vet school. Everyone always has these hyped up ideas of what happens there and what it looks like, but it was kind of anticlimactic. But again, I realize the cool stuff is probably what they couldn’t show us.
Having said that, the museum was really interesting. Looking at all the things in the Ebola exhibit, as well as the different water purification techniques, made me realize how lucky we are in this country. I think it’s wonderful that such efforts are being made to help out the under-developed areas. I enjoyed the lower levels of the museum more than the ebola exhibit just because there was more to it. The guinea worm: gross…but extremely gripping. The epidemiology of murder was a super cool out-of-the-box idea to think about and it was fascinating to see examples of the advancements of technology through the ages.
I also deeply appreciate the knowledge of our tour guide. That was a big place, with a lot going on all the time, and she seemed to know a great deal about several things and was comfortable explaining it. I share having a great passion for the career I want to pursue so I can totally appreciate her enthusiasm. The gate guards had a great sense of humor as well. All in all, it was a good experience, I was very happy for the opportunity, awesome way to wrap up the semester.
So I found a super cool article about the ecology and distribution of Bacillus anthracis. I was a little surprised to find such an article because there is either very little research done on that subject of this disease system or it’s not very current. This article explained an interesting approach to try to model the bacteria’s geographic distribution using genetic algorithms and prediction modeling. There are several factors to consider when attempting to determine the niche of a species. The study explained in this paper included using the history of wildlife and livestock outbreaks in the United States, vegetation, precipitation, and elevation. Efforts were focused on an area from southwest Texas to Minnesota.
In the U.S. disease control relies heavily on prevention via vaccination, and proper disposal. It’s unrealistic to vaccinate all wildlife so our next best defense is to understand the ecology of this disease. If we know the how’s and when’s and why’s of a disease, it is easier to predict the likelihood of where it may surface and we can be there to stop it before it becomes an epidemic situation. Prevention is always preferred over containment.
Since my disease system is caused by a bacteria that needs to be ingested to spread, space plays in a role in that if everything is super spread out, a greater distance between infected soil and other populations may mean greater difficulty for the bacteria to spill over or cross contaminate. People in North America aren’t as likely to consume infected meat from sub-saharan Africa. It is possible, just unlikely. As far as how time influences my disease system, these spores can survive dormant in the soil for decades upon decades…tough break for us, it’s not something we’re going to outlive. For all we know it’s basically always been there and will always be there. So again, understanding the space ecology better prepares us to deal with any outbreak situation whether it be natural, industrial-contamination related, or a bioterroristic attack.
(Link to super cool article below)
Although the disease-causing anthrax bacteria (Bacillus anthracis) has been around for a very long time and some would argue that it’s ‘prime peak time’ has long since been over, there is concern for the very real threat that is a re-emerging disease. Anthrax primarily affects large herbivores and grazers; human transmission is linked to things like rural agricultural activities, livestock trading, or industrial processing.
Investigations were conducted from 2009-2010 in rural Bangladesh following reports of 14 anthrax outbreaks. 140 animal cases and 273 human cases were documented, 91% of which were involved with butchering infected animals, handling contaminated raw meat, or having contact with contaminated animal skin at local meat markets.
In areas like Georgia, (a small country on the southwestern border of Russia, northeast of Turkey) reports of anthrax outbreaks have increased more than 5 fold from 2010-2012. This country hosts some rural areas that have been deemed high risk due to the percentage of population that comes into contact with possible infection. With the slaughter and butchering of livestock for the markets, meat’s not getting inspected properly and transported far distances to other markets to be resold. This allows the contamination to spread quickly.
In areas such as these mentioned above, the level of risk comes from the contaminated product of the large herbivores. The dilution effect suggests greater biodiversity means less likelihood of spread of infection but since anthrax is caused by a bacteria, it’s not a virus, it has no vector, it doesn’t really discriminate on the large herbivores that graze on the soil it lies in.
Sources:
Anthrax is believed to have been around for centuries and has been considered a biological weapon threat for about the past 60 years. Treatment of this disease relies mainly on vaccination and long-term antibiotics administered over the course of several months. The most common drugs used to combat the disease include penicillin, amoxicillin, doxycycline, and ciprofloxacin. The concern is with the emergence of more antibiotic resistant bacteria the longer we use these drugs.
Studies have been done to demonstrate the potential for development of resistance to the anthrax bacteria and it’s been concluded that because the treatment for this disease is prolonged, it is important to continue monitoring how the resistant strains of bacteria evolve. One such experiment is shown here: anthrax resistance study
As populations grow, more area is developed, gaps are bridged, and resources can be more easily shared, but so can disease-causing pathogens. If you have an urbanized area with wall-to-wall densely packed housing on top of easily-contaminated food and water sources, it’s the perfect environment to spread disease. Also with international travel becoming more readily available, so too are the pathways pathogens can travel from place to place. The best way to arm ourselves against this very real threat is proper planning, monitoring, and constant adjustments to improve global health and decrease the spread of infectious diseases.
The dilution effect suggests that biodiversity influences how effectively diseases are spread. It says an increased presence of different species will essentially ‘dilute’ the disease. With something like anthrax, being spread by the ingestion of grazers and passed through their products, it’s hard to say whether or not biodiversity has any effect at all.
Anthrax is a bacteria, not a virus. It’s spores lay dormant in the soil and are taken up by herbivores at the beginning of the cycle. True, the likelihood of the disease being spread might increase if there is a greater number of grazers, but it doesn’t necessarily matter if the grazers are made up of cattle or deer or goats or a mix of all 3.
When a vector of a disease feeds on an organism that cannot transmit the infectious agent, the disease will ultimately die out. Anthrax has no vector but if there was a great number of grazers that were somehow insufficient hosts for the bacteria, then yes there might be a lower number of cases of human contraction and the dilution effect would have greater support. What can be said is that ecosystem disruption most certainly has major impacts on the spread of infectious diseases.
The bacteria Anthrax basically stops the body from being able to fight back. It ‘paralyzes’ the immune system starting with neutrophils. The body’s white blood cells are your first defense against infection. Without them being able to travel throughout the body and fight off invading bacteria, the bacteria is free to run rampant causing damage as it sees fit.
What’s so dangerous about the disease anthrax is we’re not entirely sure exactly how it accomplishes this feat of rendering the immune system immobile and exposure to the disease often proves fatal. If contracted by any one of 4 ways, it can cause lesions and ulcers on the skin, fever, chest pain, shortness of breath, nausea, vomiting, diarrhea, and abdominal pain. You can imagine how intense the suffering if you exhibit any of these symptoms for a prolonged period and your body was powerless to heal itself.
The photo below shows a neutrophil engulfing some anthrax bacterium.
When the very first cell becomes infected, it’s immediate response is to communicate the threat to the other cells so a defensive strategy can be coordinated. The key signaling molecule is ATP (adenosine triphosphate) and when this molecule is released from an infected cell, it is sensed by receptors and welcomed by another cell who then activates a complex called the inflammasome. This complex’s job is to release immune-activating molecules into the bloodstream to get all the cells in the body prepared to defend against the incoming attack.
But if this process cannot happen and communications are severed, the body and immune system cannot prepare for such an attack. A disease like anthrax can run unchecked and result in extremely high mortality rates.
If caught early enough and the necessary resources are available, anthrax can be treated with very strong antibiotics intravenously and new research is being done with monoclonal antibodies. Although it cannot be spread from person to person, outbreak situations should be handled with care and decontamination procedures strictly followed. Decontaminations recommend to wash with antimicrobial soap, treat with bleach, chlorine, or formaldehyde, boiling, and burning. Until we better understand this disease and how to help our body combat it internally, the best defense we have is early detection and vaccination.
Apologies for anyone who’s tried to use my blog for the test, I’ve been having some difficulties with it getting it to save any information I put up. This is me attempting to once again rectify that.
I have found and included this article: Anthrax article that details some simulations run with models to determine in which way an anthrax biological attack would be more detrimental to the population. I could not find any information about the SIR model being used specifically but the researchers in this article used a variation called the Incubation-Prodromal-Fulminant (IPF) model. They chose this revision because anthrax is not a contagious disease. Infectious, but not contagious. So in changing the model slightly, they were able to focus on the 3 stages of disease progression: incubation, prodromal, and fulminant (IPF). It is a comparable variation to the SIR model so I found it appropriate to include.
As a variation of the SIR model, the IPF also assumes the limitations of a consistent population and reports in terms of response states rather than symptoms for only one disease at a time. If it tries to model the effects of multiple diseases at once, things get too complicated to follow.
Having said that, there are also some key advantages to point out. These models (SIR and its variants) are well-known by the medical community and the ones behind writing policy. Also, once the probabilities are understood this model can be developed to predict very far in the future very quickly. And perhaps the biggest reason they are still in use today is of how economically and cost efficient they are.
Let’s take a closer look at the epidemiological triangle and apply the specific disease: anthrax. The triangle’s 3 legs represent the agent, the host, and the environment, all connected by a vector. Anthrax is caused by a rod-shaped, gram positive bacterium (agent) that rests in the soil and can survive there for years. These bacteria are ingested by herbivores (host) during grazing on the vegetation that grows in the “infected” soil (environment). Once ingested, they multiply inside the animal and produce a toxin that typically causes death in a few days to a few weeks.
Anthrax is a zoonotic disease so it is spread to humans by way of contact with the bacteria spores, usually through tainted animal products. If you were to eat meat or drink milk from an infected cow, that’s the bacteria’s way into your system. Interestingly enough, it’s not typically spread from human to human and it’s not really a vector-borne disease.
The soil or even dried or processed animal hides can provide a sustainable environment for the spores of this bacteria for decades. As far as coevolution, I feel like both the bacteria and the reservoir hosts have always been here. There’s always been dirt and grass and herbivores to feed on it, we’ve just domesticated these herd grazers. The natural reservoirs of this pathogen are our domesticated herbivores (cattle, sheep, goats, etc.) and by grazing these animals directly consume the bacteria and then pass it along to humans through their products we harvest from them (meat, milk, cheese, skin/hair, etc.)
It’s not something that’s a huge concern for developed countries anymore, unless it’s used as a bioterrorism weaponized agent, however in small countries like Zambia and Zimbabwe there have been substantial cases reported simply by the typical spread of the agent through contaminated animal products. In September 2011, there were 511 reported infections and 5 deaths in a wild game management area where 85 hippos had died from the infection. A large number of people were cross examined (241) and of those, 84% confirmed eating hippo meat before the outbreak so, it is real, and it could kill you.
WILD 4970-004 