Inimesed 15 Mar 2011  EWR
    Trüki   E-post   FB     
Illar Tenno, DVM Illar Muul, PhD

In dealing with Lyme disease, understanding ticks and their ecology is essential. But, ticks also carry other diseases. Since we wrote the last article, we met a man in Maryland, USA, who has been granted full medical disability. He was found to be infected by Lyme disease spirochetes and simultaneously by Babesia, a blood parasite similar to malaria. Antibiotic treatment against spirochetes has little affect on Babesia. His chronic symptoms are very complicated. He did not spend much time outdoors but his dog shared his bed, and spent time outdoors.

In addition, we have found in the literature cases in which Lyme infections were transmitted together with Ehrlichia, another spirochete that has been identified just decades ago to cause illness in dogs, especially fatal for Alsatians and Beagles.

Limits of Medical Knowledge

Apart from their medical importance, ticks evoke a revulsion in most people. Very few would want to keep them as pets. This reaction may be partly inherited; a trait that survived after generations of strong avoidance of ticks and thus avoiding diseases that they carry. Those who were indifferent were more likely to get sick and die.
Consequently few people study Acarology (Study of ticks and their relatives) and few funds are available for research. IM’s friend, Harry Hoogstraal was the world’s expert in Acarology, but had to subsidize his research largely from money from his family’s “chocolate fortune.” When he died in the 1980’s, his research reference collections were moved from Cairo to the National Museum of Natural History, USA. The crates sat in the hallways for years. We do not know who the current expert is.

Research Bias

The limited funds for disease research go mostly for cures and vaccines. Very little is devoted to field studies that could illuminate the ecology of diseases and their vectors and could lead to prevention of these problems. As a result, attempts to control “vector-borne diseases” (transmitted to humans by way of species such as ticks, lice, mosquitoes, etc.) are often ineffectual or may involve harmful side-effects. We provide this introduction to explain why the medical profession is so helpless in managing vector-borne diseases, not just Lyme, but malaria and many other important diseases throughout the world.

The historic approach has been to “spray and slay” vector species. This has been only partially successful, in limited areas, for limited increments of time. We will not go into problems of environmental pollution and human health effects. Also, ticks and other disease vectors have become remarkably successful in developing resistance to a long succession of “newly” developed pesticides.

What Can Be Done?

The most important step to take is to avoid ticks and tick bites. If you can’t avoid tick habitats, or do not want to because you like hunting, fishing, camping, picnicking, or just enjoy nature, you can apply repellents that contain DEET to your shoes and trousers. Do not apply to skin. DEET is absorbed through skin and long term exposure can be harmful.

Tick larvae that transmit Lyme disease are small and prone to dehydration, so they do not climb up high on vegetation. Also, they are attracted to small animals, like mice, so they do not need to climb high. They do not jump, as some people believe.

Ticks and Pets

Pets, especially dogs, can bring ticks indoors. Tick control on dogs is usually standard practice. Sleeping with pets can be risky. Once attached, a tick will usually not look for a second meal. However, some are fussy and search for a long time for a favorable site for attachment. That could be you. The softer the skin, the more attractive it is (not just for ticks). On dogs, ticks usually end up in or on ears, groin region, between toes, etc.

Tick Checks

If active outdoors, you should end the day with a search for ticks, especially in “tender” areas and private places. Humans are built in such a way that we cannot bend and see all of our surfaces. Mirrors are helpful, but larval ticks are very small. If camping, adequate light to see these “guests” may be a problem. When showering, keep the lather on your body for several minutes before washing it off. This is especially effective against chiggers (smaller cousins of ticks) which are very difficult to see.

If during the night you feel an itchy spot, you may discover a tick you missed earlier. Adult ticks secrete through their mouth parts a liquid that solidifies like cement, so they are very difficult to pull off in one piece. Tweezers with very fine points are helpful to get between the head and the skin. If the tick is removed within 24 hours, the infection is less likely to establish itself.

Area Control

Cutting vegetation short can be helpful, keeping the ticks close the ground and more exposed to predators and sunshine. Ticks avoid direct sunlight. When camping, spray the ground around entrances to tents and where you are sitting. Be careful around camp fires since most sprays are flammable. You can sweep the ground and put the litter, including the ticks into the fire. Engorged ticks explode with a pleasant-sounding “pop.”

Around Your Home

Cut, rake, and sweep areas in which you are active. This needs to be done only in the warm months (night temperatures above 100C (500F). Allowing free ranging by chickens can help keep down insects and ticks. Guinea Fowl (domesticated African bird) have a strong appetite for ticks and they supply a lot of tasty meat. If you have many ticks, feeding costs will be low.

Keep rodents under control. Larval ticks feed on rodents. Remember, this disease does not infect every tick or every rodent. Some areas have high infection rates; in other areas they are lower. But, whatever the infection rate may be, more rodents means more food for ticks. Larger tick populations drive up infection rates in people.

Things to Remember

The ticks do not “want” to give you the disease. They just want a meal. The parasite gains no advantage by making you ill. We get ill because we are in a period of instability in our relationship with the Lyme spirochete. In some places where people have life-long exposure, beginning in early childhood, antibody rates are high (indicating repeated infections), but clinical disease is rare.

Things We Could Do

1. Multivalent vaccines (against many strains) could be administered to people at risk, beginning in childhood. This includes people who do not spend much time in the great outdoors, but like to share their bed with their pet that does spend time outdoors. Even a vacant lot in a city can support mice and voles, and ticks. Birds can transport ticks from one area to another, including infected ones. Vaccines will not eliminate infections, but they help reduce the seriousness of the results.

2. Mice and voles do not “want” to be infected. If we set up feeding stations, with food heavily “laced” with antibiotics, the rodents would not re-infect the ticks. However, keep in mind that some female ticks pass their infection through their ovaries, to their eggs and ultimately their larvae. So, infection rates could be reduced, but the spirochetes would not be eliminated entirely. It is a game of chance. That is why we need to know the infection rates in different kinds of rodents and ticks, and how these rates vary through the year.

3. Deer populations must be controlled. Natural predators are not abundant enough to do the job. IM spent much of his time in forests throughout his life. In the 1950’s in New England, USA, he saw no deer. On rare occasions he saw tracks. Deer were a necessary food source in many areas, so they were heavily hunted. And, venison was considered a delicacy. In the decades starting in the 1960’s, agricultural practices changed rapidly. In the eastern U.S., much of the marginally profitable farmland was abandoned from agriculture and forests were restored. Deer were released from fenced military areas where they were protected and eventually over-populated most areas. Public attitude toward hunting changed drastically. The reproductive potential of deer increased. In the 1970’s, twins were seldom seen. Now even triplets are not uncommon. In Maryland many does have fawns twice a year.

Both of the authors love animals and our careers are devoted to their welfare. However, to us there is no doubt that deer herds the sizes we see currently are not good for the: 1) environment, 2) human safety (automobile accidents), 3) human health, and 4) the welfare of the deer. Malnutrition, starvation, and disease epidemics are cruel forms of death. So is dying in the claws of a predator. In natural ecosystems, few animals died peacefully of “natural” causes. The causes were weakness from malnutrition, injury, disease, or old age, all of which led to being violently killed by a predator. A well aimed shot is far less painful than being torn apart while still alive.

So, How Can We Control Deer? Most people will not revert to hunting. Also, in highly urbanized areas hunting could be disastrous. So, other alternatives need to be considered to reduce deer herds around human habitations. A “well aimed shot” need not be a bullet. Tranquilizer darts could be equally effective.

Birth control has been discussed, but implementation has been difficult. One method could be based on the craving for salt by all herbivores. Hormones and chemicals that inhibit reproduction could be incorporated in the salt. If livestock are present, the salt-lick can be placed in housing that would be built too high for sheep and too narrow at the opening to allow cattle to reach the “salt.”

The laced “salt” would also reduce rodent populations locally. They also crave salt. Deer move over large areas; rodents are more confined. Birth control will not eliminate the deer, or rodents, but will reduce their populations. Together with feed for rodents laced with antibiotics that would reduce their parasite loads, such a strategy would reduce infections in humans and their pets. Reduced deer herds would also save native plants that are approaching extinction, and prevent many automobile accidents. Perhaps Lyme disease is the “wake-up call” to address a complex set of environmental problems.
    Trüki   E-post   FB     

Vaata veel ...

Lisa uus sündmus