Tick-borne diseases - recent increases in cases

[Astronuc]

We have a related thread on Powassan virus
https://www.physicsforums.com/threads/powassan-virus-on-the-rise-in-the-us.1016929/

Washington Post (Yahoo) reports: A deadly tick-borne epidemic is raging. Dogs are key to ending it.
https://news.yahoo.com/deadly-tick-borne-epidemic-raging-171617610.html

EJIDO PADRE KINO, Mexico - The boy came home from school weakened by fever, his ears burning-hot. Over the next few days, the 7-year-old got sicker - vomiting and complaining of abdominal pain, his mother recalled. Then, the telltale red spots appeared on his hands. But none of the doctors in this rural community along Mexico's Pacific coast recognized the warning sign for one of the most lethal infectious diseases in the Americas - Rocky Mountain spotted fever. A week later, the boy was dead.

The following year, in 2020, the disease killed a 5-year-old boy in a nearby house. Then last October, a few blocks away, another 7-year-old succumbed to the same scourge.

My wife and several friends have had tick-borne illnesses, usually treated with antibiotics. However, some have had serious health consequences, probably because the diagnosis happened well after the infection, and treatment was not soon enough.

The disease, spread through the bite of an infected tick that lives primarily on dogs, is rare, but its incidence is rising. It has reemerged at epidemic levels in northern Mexico, where more than 2,000 cases, resulting in hundreds of deaths, have been reported in the past five years. Young children have been hit the hardest. In the Mexican state of Baja California, where Ejido Padre Kino is located, there were 92 cases in 2022, more than double the previous year, according to state data.

Alarm has risen in recent years as warming temperatures intensify tick activity and disease risk. Cases of malaria, dengue fever, West Nile virus and Lyme disease - infections transmitted by ticks and mosquitoes - have increased. Scientists worry that Rocky Mountain spotted fever, first identified in western Montana at the beginning of the 20th century, could spread to more regions.

 

[Laroxe]

I really wish that people would stop trying to link the spread of vector born diseases to changing temperatures. I have yet to see any evidence of tick activity intensifying, and a variety of ticks with the potential to spread disease have very wide ranges. People forget that diseases like malaria were far more widespread that they are now, in fact Malaria was endemic over most of Europe from the Neolithic period before being eliminated in the 1970's.

Vector born diseases reflect interactions between the vector, animals and humans, and the vector has to be infected, usually by contact with one of the others. We are currently in a period of time in which humans and their animals have become common in virtually all environments and they are highly mobile. The introduction of Zika virus to the America's provided an informative case study and the banning of DDT lead to a surge in malaria in Africa, with some countries reintroducing it.

The threat of vector born diseases is a very real one and one which the global community has yet to address properly. Unfortunately, it won't be addressed, until people start to identify the specific problems and the ways to address them.

 

[hutchphd]

I have yet to see any evidence of tick activity intensifying, and a variety of ticks with the potential to spread disease have very wide ranges.

You should visit my brother in Belfast ME USA on his 135 acres. In the good old days when there was snow and vicious cold every winter, the discovery of a tick on human or pet was an event that ocurred perhaps once in a summer. In the past decade this has increased to the point where any trip through high brush will guarantee multiple eight-legged hitchhikers trying to burrow in. It is godawful . I truly dislike ticks, and personal abatement is now both time-consuming and difficult.
So in Maine it most certainly is intensifying at an alarming rate.

 

[Laroxe]

You should visit my brother in Belfast ME USA on his 135 acres. In the good old days when there was snow and vicious cold every winter, the discovery of a tick on human or pet was an event that ocurred perhaps once in a summer. In the past decade this has increased to the point where any trip through high brush will guarantee multiple eight-legged hitchhikers trying to burrow in. It is godawful . I truly dislike ticks, and personal abatement is now both time-consuming and difficult.
So in Maine it most certainly is intensifying at an alarming rate.

Well, I'd certainly like to visit Maine it looks very nice, but the link to a site specifically addressing the problem of Tics in Maine, suggests it's a recognised issue. Apparently there are around 15 different species of ticks found in Maine, and apparently cold winters are less important than we might think. Most of these species go through 3 developmental stages, changing their preferred prey animal at each stage, unfortunately, they will feed on humans during each stage. Several have a life cycle stretching over two years, they can overwinter by becoming dormant, the females die after they lay their eggs.

Ticks are known to carry quite a few different pathogens, which they pick up from their first prey animals, the publicity around Lyme disease may have increased people's awareness. Of course, the presence of pathogens in their prey populations will be reflected in the rates of disease. I suspect that increases may reflect the ability to diagnose some of the newer infections, even with Lyme disease, it's only recently that it's been seen as a real infection. The ability to transmit these pathogens to new hosts varies depending on the tick species, but generally, the likelihood of infection increases with the time the tick remains on a host feeding and some can remain in situ for several weeks. This is why it's important to check and to remove them as soon as possible after entering the countryside.

The population of ticks in an area tends to follow predictable patterns and is highly dependent on the availability of prey animals, new transient populations often arrive in animals, including birds. At least with tics there are quite a few ways that we can use to reduce risk and simply reducing long vegetation near to human habitation, insect repellents and covering exposed skin are very effective, treating pets with long acting insecticides has the potential to decimate their population.

https://extension.umaine.edu/ticks/maine-ticks/

 

[256bits]

on the availability of prey animals

One deer per every 5 sq km in the 1940's to 8 to 9 deer per square km by around 2003.
The abstract doesn't say the wolf, coyote, or other predators of deer population during this time, but naively I would assume that the predator population has decreased.

I do think that the populations follow a similar pattern in the NE states and southern quebec, just from headlines and reports I have herd ( sic ) over the years.

So rather, as you have said, warming may have some thing to do with the tick population ) , also does carrier populations of animals in the wild.

 

[hutchphd]

he population of ticks in an area tends to follow predictable patterns and is highly dependent on the availability of prey animals

Thats why we call it an ecosystem.

Well, I'd certainly like to visit Maine it looks very nice, but the link to a site specifically addressing the problem of Tics in Maine, suggests it's a recognised issue.

It was much nicer 20 years ago (when I lived there) before recent induced climatic alterations.
Yes it is recognized. I was simply impuning your definitive statement

I have yet to see any evidence of tick activity intensifying,

Now you have such evidence. I don't know why the predator -prey relationships are salient. It is, of course, very complicated.

 

[Laroxe]

My concern about the links being made to climate change and vector born diseases is a very pragmatic one, we are faced with an emerging threat from tick born disease and understanding the nature of this threat is the only way we will effectively manage it. There are around 900 species of ticks, and they occur in every country, including Antarctica, around 90 species are found in the USA. We already know that many of the new infections that we see have emerged as humans increasingly enter regions, that have never been visited before and are exposed to pathogens that have until then only occurred locally. Humans also quite frequently introduce new species of animals to an area. Such individuals, if they survive, may then return to areas with high human populations, potentially exposing others to these new pathogens.

Ticks are not really very popular, they parasitize a large number of different animals as they need a blood meal to advance through their life cycle. Different species of ticks have preferred prey animals but quite a number can be opportunistic feeders, humans are generally targets of opportunity. The recognition that ticks may spread human diseases has already led to a significant amount of research to identify which species are capable of transmitting which diseases. Of course to transmit a disease, the tick must first drink a blood meal from an infected host, either an animal or another human, then bite a human, the feeding must occur over a sufficient period of time to allow an adequate inoculum of a pathogen.

The risk of disease transmission has nothing to do with increased activity because of warm weather beyond its usual seasonal behaviour. In fact ticks are hardly known for their active lifestyle, they simply sit and wait for a potential prey animal to pass, what is being noticed is the increasing incidence of infection and this reflects the level of infection among its previous blood sources. The tick is in fact a fairly passive link in a chain of transmission.

It is in fact the change's in the behaviour of humans that has played the greatest role in introducing new pathogens into an area. This has been accompanied by extending urban sprawl into the countryside and the increasing popularity of being out in the country, as we have removed many of the earlier risks associated with being out in the wilds. Now, while warm weather might encourage that increased contact, it doesn't explain very much about the increased incidence of disease or indeed how best to manage this. The observation that the countryside in Maine has hanged is an interesting one, though I suspect it would be difficult to attribute that to warming. It's perhaps the observation itself that is useful because it's that that can help us understand the problem. I just think that the trend in attributing virtually all problems to global warming without clear evidence or an explanation, takes us nowhere and may in fact distract from what we should be doing. This isn't an attempt to discredit climate change, the climate clearly is changing, I just think when we are trying to address specific problems, we need to keep our eye on the ball.

 

[hutchphd]

I suspect it would be difficult to attribute that to warming

I do not understand why you believe this. I think extreme temperatures are very often indicia of habitability ranges for species. Although the range for ticks is mediated by the natural range of the significant host species, these are also climate sensitive and so the effect can be secondary or tertiary. In turn the population of host animal species is driven by extant plant species whose range is demonstrably climate driven (I live in climate zone 5 at present according to the purveyers of plants).
The distribution of population in mid Maine is changing but the past decade has not been particularly aggressive. You are correct that I assumed you to be a climate "deny-er" and I apologize for the tone.

 

[Laroxe]

Well, my concerns. The main issues in Tick born diseases that need to be addressed are;
The routes of the infectious agents into the Tick population - this is an issue really about human behaviour.
How exposure to the pathogen is maintained in the tick population - each tick represents a new exposure.
Understanding the variations in tick physiology which control their ability to transmit infection.
Which animals are involved in maintaining infection, of which diseases and the monitoring of new disease causing organisms.
We need more precise epidemiological information, particularly related to human behaviour, infection rates among ticks and in the range of their prey animals.
We need much better clinical information for prevention, diagnosis and treatment of the actual diseases.

While its true that local climatic conditions are important in understanding the range of organisms that can live there but ticks are able to establish populations in every continent and in some of the most extreme climates. This implies that there must also be prey animals available for them to reproduce effectively, for the ticks themselves plants are not essential.

I do recognise climate change as an important issue and one which is likely to require a huge effort to try and address. My concern is that the seemingly fashionable trend to blame everything on global warming, has become a significant impediment to action. While you might not agree with me, this is an issue that is getting increasing attention, with a great deal of literature now being devoted to "attribution science" in climatology. The concern is that the large number of claims, unsupported by evidence or indeed sense, is damaging the credibility of the whole of climate science and even distracts from identifying the real causes while reducing political accountability. An organisation with wide links has been established, which you might find interesting called "World Weather Attribution" info is readily available on google.
This provides an interesting overview of the issues.
https://link.springer.com/article/10.1007/s13194-023-00516-x