Tag: one health

Can We Summarize One Health?


https://veterinaryrecord.bmj.com/content/vetrec/174/4/85/F2.large.jpg

Not likely, but I’ll do my best.

In case you weren’t aware, this blog was the result of a class assignment, encouraging me to research and study different One Health topics and present them in a blog. Needless to say, I learned quite a bit that I was previously unaware of, or had never thought of; not only in the topics that I presented in my blogs, but also in the class discussions.

One Health is a very broad and encompassing subject. All over the world, organizations like the Center for Disease Control and World Health Organization monitor serious diseases and mobilize efforts to control them. They are constantly preparing for serious outbreaks like Ebola and Zika, but those aren’t the only problems plaguing the world. Neglected Tropical Diseases, which are rarely seen in the United States and are easily treated here, ravage less well-developed areas where there is limited access to basic treatment and preventive care. These maladies are no less important in our efforts to make the world healthier.

However, we also covered other topics, such as the emergence of increasingly resistant microbes to antibiotics. Much blame is placed on where we believe the problem originally arose, but in actuality there has been and continues to be irresponsible use everywhere. Prescribing antibiotics for a problem that doesn’t need them, or when they wouldn’t be necessary; failing to finish out the entire antibiotic prescription, and even saving them to use again later; using subtherapeutic levels for growth promotion; both human and animal medicine have failed to use these powerful drugs judiciously. And now, as developing countries increase their use of antibiotics and do not take into account this very serious result of misuse, the danger only increases. And it’s not just microbes that are developing resistance. Insects that carry serious diseases are becoming resistant to insecticides, the most notable example being malaria-carrying mosquitoes. We discussed that control is the best strategy for these problems, as there are currently no new drugs or compounds being developed.

We also learned about what happens when control measures have failed and an outbreak occurs. There is an organized stepwise process that takes place, starting with determining the list of problems and hazards, then moving on to assessing and communicating the risks. Treating the disease is actually one of the last steps. First, it is necessary to quarantine and control movement of the disease to prevent further spread, and then determine what it is that needs to be treated. It is a multifactorial problem that requires cooperation from multiple disciplines in order to effectively eliminate it.

Of course, human, animal and environmental health aren’t just impacted by diseases. Pollution is a serious problem affecting people all over the world, especially in heavily populated areas and in developing countries. Illnesses caused by breathing polluted air and drinking polluted water are serious problems where industrial waste is not well controlled—as seen in China—and poor areas where there are no water sanitization facilities. On a more detailed note, I learned about how many facilities and environments can be carefully designed to control and prevent disease, or improve the experience within. For example, I never knew how much detail went into water fountains to make sure that the opening where the water came out wasn’t contaminated.

One Health is more prevalent than most people know. Hardly any problems affect only humans, or only animals, or only the environment. And it doesn’t just encompass diseases, either. The concept of One Health is that all three groups are interconnected when it comes to health and wellbeing. Obviously, this is very true for most every situation. One Health should be more widely spread and discussed. Through education efforts, we can make people aware of the impact we have on animals and the environment, as well as the impact that animals and the environment have on us.

The First Non-infectious NTD

The World Health Organization has a list of diseases, called neglected tropical diseases (NTDs), that they are working to control through widespread public health policies. These are diseases that are prevalent in tropical and sub-tropical climates in which “Populations living in poverty, without adequate sanitation and in close contact with infectious vectors and domestic animals and livestock are those worst affected.”[1] One of the more recent diseases, as well as the first non-infectious disease to be added to the list, is snake envenomation.

Why was “snake-bite” added to the NTD list? Most people don’t often think of it when someone mentions ‘disease’. There are four criteria that must be fulfilled to be placed on the World Health Organization’s neglected tropical disease list.[2]

  1. Significant burden of the disease; many people are affected, and many die.
  2. Majority of cases occur in tropical or sub-tropical geographical areas, and impacts the poor in particular.
  3. The impact of the disease can be mitigated through treatment and prevention.
  4. The cost of researching and implementing prevention strategies is ultimately cheaper than the disease’s impact.

Snakebites meet all four criterion. 250 species of dangerously venomous snakes are present in 160 countries around the world,[3] and snake-bite encounters occur around 5.5 million times every year. Of these, WHO estimates that 400,000 victims suffer permanent disabilities, and up to 138,000 do not survive.[4] The majority of these bites take place in sub-Saharan Africa, South Asia and South-East Asia where the majority of the world’s population is concentrated. The groups at the highest risk of potentially-fatal bites include poor rural dwellers, agricultural workers (including farmers, herders, fishermen, and hunters), children, pregnant women, and any with restricted or no access to healthcare.[5]

WHO believes that their estimates for the number of snakebites that occur is drastically lower than the actual number of cases, because around half the victims in poor areas will make use of traditional medicines rather than seeking more advanced medical attention. Though this could be due to cultural reasons in some cases, in many others it is because the victims do not have access to proper care.[6]

Antivenom is one of the most common and effective methods of dealing with snake envenomation, and it can be relatively cheap to produce. However, the quality and availability of antivenom can be very limited, especially in poor areas. Inadequate product safety and efficacy, lack of properly trained health personnel, absence of neutralization specifications, and local superstition surrounding snakebites, all contribute to inaccessibility of medical care. Many companies attempting to produce good quality antivenom are driven out by lower quality products sold at cheaper prices.[7]

https://www.who.int/snakebites/antivenoms/Cycle_of_antivenom_market_decline.pdf?ua=1

To effectively be able to provide medical care access around the world, it is not enough to produce vials of antivenom. Like with the other NTDs, a multi-pronged One Health approach will be the most effective strategy. The antivenom must be of tested and guaranteed quality, ensuring effectiveness. Public education programs must also be implemented, to encourage locals to seek proper medical attention after a snakebite, as well as direct them to trusted sources for their antivenom. Protective footwear to protect from bites, netting or other barriers to keep snakes out of homes, keeping paths and other areas clear of refuse piles to reduce hiding places, and cutting grass short to make snakes more visible, are all effective environmental strategies to prevent snakebites.[8]

[1] https://www.who.int/neglected_diseases/diseases/en/

[2] https://www.who.int/snakebites/snakebites_FAQ/en/index1.html

[3] https://www.who.int/snakebites/disease/en/

[4] https://www.who.int/neglected_diseases/news/Snakebite-envenoming-mandate-global-action/en/

[5] https://www.who.int/snakebites/epidemiology/en/

[6] Ibid.

[7] https://www.who.int/snakebites/antivenoms/en/

[8] https://www.who.int/snakebites/snakebites_FAQ/en/index6.html

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How’s About the Epidemiological Triad?

An epidemiological triad is a tool used by One Health professionals to not only identify and categorize a health issue, but to also develop a control plan.

This is a general example of an epidemiological triad.

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It has three corners: host, agent and environment.

The ‘agent’ stands for whatever it is that causes the disease. This can be a virus, a bacterium, a toxin, etc. We need to make a distinction between the disease itself and the agent that causes it. The flu disease consists of the common flu symptoms, but the agent that causes the disease is the Influenza virus. Just because someone is infected by the Influenza virus, doesn’t necessarily mean that they will get the flu disease; for example, if they are healthy and have gotten a flu shot, they will be less likely to get sick. In the ‘agent’ section of the triangle they list all the features of the agent that may cause disease.

The ‘host’ is whatever the agent can cause disease in. Some species are resistant or immune to certain agents, and will not come down with the disease even if they are infected. Some animals are naturally resistant to disease by the agent unless certain conditions are fulfilled; for example, if the animal is young, old, stressed, starved, or otherwise weakened. In this section of the triangle they list all the conditions that could predispose a possible host to contracting the disease when infected by the agent.

The ‘environment’ section stands for the environmental conditions that could increase chances of a host coming into contact with the agent, and make the host more susceptible to contracting the disease. In this instance, if the geographical area is favorable to the agent’s survival, if the host is constantly in close contact with infected individuals, has limited access to medicine or sanitation, or other conditions that may make disease more likely.

Here’s an example of an epidemiological triad for an actual disease, Scabies:

This disease is caused by the agent Sarcoptes scabei, a microscopic mite. The unique thing about this agent is that cases of disease are very uncommon in developed countries where most inhabitants have access to healthcare, and are not overcrowded. In developing countries, however, it is one of the most common causes of skin diseases, and is most prevalent in tropical areas where the mites survive best.[1] For this reason, scabies is considered a neglected tropical disease: a disease which disproportionately affects “populations living in poverty, without adequate sanitation, and in close contact with infectious vectors.” [2] Young children and the elderly are particularly susceptible to contracting scabies, as well as secondary complications.

A triad like this is used to find possible control points in the disease cycle. The agent could be controlled by administering scabicide, a medicine that kills the mite. Prevalence of the disease could be lessened by controlling the disease in the stray dogs that can transmit the mite to people.

The triad could also be used to identify areas and situations at high risk for scabies outbreaks, and allow surveillance and preparations to react in case one actually takes place. Right now the World Health Organization recommends mass administration of scabicidal drugs as the most feasible and effective method of controlling the scabies disease.

The epidemiological triad is a good example of what One Health is about: taking into account the whole picture of what leads to disease, by listing and investigating all the factors. Looking at ways to intercept and stop the disease cycle, and not just focusing on treating those who are already infected. Working for the improved health of all people, as well as animals and the environments they live in.

[1] https://www.who.int/neglected_diseases/diseases/scabies/en/

[2] https://www.who.int/neglected_diseases/diseases/en/

Let’s Talk About The Dilution Effect

What is it? Why is it important?

The Dilution Effect theory has been studied and discussed for several years, now, and if you’re involved in conservation, ecology, One Health, human or animal disease, or other related areas, it’s probable you’ve heard the term.

So what is the Dilution Effect?

The term was popularized in a study performed by Richard Ostfeld and Felicia Keesing, which they published in the Canadian Journal of Zoology in 2000[1]. They studied a deforested habitat where the prevalence of Lyme disease among the people living nearby was far greater than elsewhere in Lyme-endemic areas. What they found was that it had a lot to do with the wild animal population. Specifically, the white-footed mouse.

Lyme is a disease caused by a bacteria that resides in the blood of an infected host. Ixodes ticks are responsible for spreading Lyme disease to people when they bite and feed off them. When these ticks are newly hatched from their eggs as larvae, they find a small animal to feed on so that they can grow and molt. That small animal can be a raccoon, bird, mouse, etc. If that animal has Lyme inside them, the tick is infected when it sucks their blood. Once it molts, it can then infect a person if it decides to attach and feed on him.

But the thing that made this particular Lyme-prevalent area unique was its population of white-footed mice. These mice, for unknown reasons, are what’s known as an “amplifier host”. This means that, when they are infected with Lyme disease, something about their biology and physiology makes them really good at multiplying the disease inside themselves and infecting the ticks that feed off their blood. You see, transmission and infection by diseases—especially ones spread by ticks and insects—is very complex. Lyme disease does not replicate and survive the same in every species. Some animals, once infected, are such poor hosts that they don’t spread it, even if a tick sucks their blood.

So this area was swarming with infected ticks and amplifier hosts, and the people living nearby were constantly getting infected. Judging by the situation, Ostfeld and Keesing determined that the way to rectify the problem would be to increase diversity of the animal population. This is the Dilution Effect. Basically, it means that if there is a wide range of animals in an area, many of them would not be good hosts and spreaders of Lyme disease. That way, when the larval tick is looking around for an animal to feed on, the odds of it feeding on an amplifier host and getting infected will be far less, and thus its chances of also infecting any human being it may happen to bite.

Ostfeld and Keesing determined four basic conditions that must be present for the Dilution Effect to apply:

  1. Vector has generalized feeding habits. Basically, the tick isn’t picky; it feeds off a lot of different animals.
  2. The vector acquires the pathogen from hosts. So, the tick is infected by feeding off an animal that already has the disease.
  3. Reservoir competence among hosts varies. This means that some of the animals are really good at transmitting the disease to the ticks, while other are not so great at it.
  4. The most competent reservoir host tends to be a community dominant. The animal that is really good at infecting the ticks (in this case, the white-footed mouse) tends to be a very popular host for the ticks to feed on.

So the idea is, if there is a wide range of hosts with a wide range of competencies, incidence of the disease in the ticks will decrease. Most other groups that found support for the theory generally claimed that large, forested areas supported more diverse populations than smaller, isolated patches surrounded by human cities.[2]

However, there has been some dissent with this theory. Linske et. al.[3] made a good point when they warned against broadly applying the concept everywhere; even Ostfeld and Keesing admitted in their paper that this rule was not universal. For example, Linske’s group studied Lyme disease prevalence in both a large, undisturbed forest and smaller woodland fragments in residential areas in Connecticut. But they found that the number of Lyme-infected ticks was far higher in the huge forest than in the residential areas. Why was this the opposite of what Ostfeld and Keesing found? The reason is that the forest in Connecticut was mature and had mostly upper canopies, which actually resulted in a wildlife population that was not very diverse. The fragmented residential areas, on the other hand, had a lot of local diversity and competition, which beautifully fulfilled the conditions for the dilution effect.

While the dilution effect is an important theory, there’s still a lot of investigating to do on this subject—not only in terms of how it works on the whole, but also how it works in specific areas. It’s important to take the entire ecosystem, its environment and animal population, into account when studying the effects of disease on human populations.

[1] http://www.nrcresearchpress.com/doi/abs/10.1139/z00-172#.XDleyExFxPY

[2] https://www.caryinstitute.org/science-program/research-projects/biodiversity-community-ecology-and-dilution-effect/dilution-effect

Allan, B. F., F. Keesing, and R. S. Ostfeld. 2003. Effect of forest fragmentation on Lyme disease risk. Conserv. Biol. 17: 267–272.

LoGiudice, K., R. S. Ostfeld, K. A. Schmidt, and F. Keesing. 2003. The ecology of infectious disease: effects of host diversity and community composition on Lyme disease risk. Proc. Natl. Acad. Sci. U. S. A. 100: 567–571.

[3] https://academic.oup.com/jme/article/55/3/681/4788748