Worms track us down with the chemical trails.
PARASITIC WORMS infect millions of people in the developing world, by following chemical trails to their hosts. Isolating the substances that attract them is the key to finding cheap and practical ways of preventing infection.
One might have observed smoky lines following the air jets in the sky. Some people in Pakistan wrongly consider them as satellites of meteorological data collection. These contrails are formed by the condensation of vapours exhausted from the burning fuel of the aircraft. Chemical trails are those originating from damaging and disease causing chemicals spread in the sky as a bioterrorism. Here we discuss the quality of worms to be attracted to the chemical trails released by humans. Throughout the day, our skins are constantly sending out messages that we can neither see nor hear. The message is written in chemical form and it says, "Here I am. Come and get me". We neither see nor hear these signals. But to those that can, they act as shining beacons guiding them crawling, swimming and slithering in our direction. These creatures are nematodes, a group of worms that are some of the most common animals on the planet.
The vast majority of nematode species are parasites, and hundreds of species count humans among their potential hosts. Unlike bacteria or viruses, nematodes actively seek out their hosts, rather than waiting to be transferred by water, a sneeze or a bite. We are facing problems in developing control and prevention methods because unfortunately we know very little about how these parasites track down their prey, giving us few options for preventing infections and this may be because they are a relatively minor problem in the world's well-developed nations. But mostly, our lack of knowledge reflects how difficult it is to study these animals. Nematodes, commonly called as roundworms, pose major health problems including: Illness, stunted physical and mental development, and anaemia. In people with weakened immune systems, just like those having HIV, the worms can breed to a point where they become fatal.
Generally, worms can lead to some or all of the conditions like: anaemia, constipation, cough, diarrhoea, eosinophilic pneumonitis, nausea, rashes in waist and buttocks, stomachache, vomiting, weight loss, etc. In the immunocompromised hosts (like those infected with HIV or any other immuno-suppressant disease), distension of abdomen, neurological and pulmonary complications, septicemia, shock and death occurs.
Just two species, the hookworms Ancylostoma duodenale and Nector americanus, infect over 600 million people around the world. Currently, over 300 million people are infected every year by Strongyloides causing a disease called strongyloidiasis. It is common in tropical and subtropical areas but also occurs in temperate zones. In addition to its parasitic life cycle, the heterogenic character of its life cycle allows this worm to live and reproduce without a host in the soil. Moreover, the act of autoinfection allows it to infect the same host over and over with any intermediate host. The larvae of worms penetrate the skins coming in contact with the contaminated soils and travel to pulmonary arteries through blood circulation. After entering the lumen of bronchi, they are coughed up and swallowed to enter the intestines to convert into mature worms. Female worms have the capability to produce eggs in the intestines of host through parthenogenesis making "strongyloidiasis" a very persistent disease.
Recently, Daniel Safer and colleagues from the University of Pennsylvania, USA, found that Strongyloides stercolis has a potential to find a suitable victim. Safer found that skin extracts of dogs and gerbils (normal hosts) had a magnetic attraction for Strongyloides, but the extracts prepared from non-host species, like cats had no effect. Further detailed studies lead to the identification of the substance from skin extracts of potential hosts which was "urocanic acid".
The urocanic acid acts as a natural sunscreen of skin of animals and humans. It is a histidine metabolite produced by deamination of histidine and is most abundant on the sole of the foot, where levels can be five to ten times higher than other body parts. Each of our footsteps creates a trail of this acid that leads the soil-dwelling Strongyloides to be the part of our body closest to the ground. This acid along with other factors like the mammalian body temperatures, carbon dioxide gas exhaled attracts Strongyloides. As we cannot control the body temperature and exhalation, we can play with the urocanic acid which has a quality to stick to divalent metal ions. Safer proposed that this quality can be utilized to stop parasites from tracking which could help to indirectly reduce the worm burden.
He further confirmed that addition of manganese, calcium or magnesium successfully hid the attractive extracts from the sniffing worms. This is encouraging news. It means that topical application of creams containing these metals to vulnerable body parts like feet could provide a cheap and practical way of preventing Strongyloides infection. Foiling this species along would have great implications for global health, and doing so cheaply and easily would be ideal for the developing countries. Chemicals can kill the adult worms, but least effective against the larval stages which in most of the cases are infective and can travel through infected bodies. In this scenario, preventing infection is the best option. Safer's work provides hope for a breakthrough, and has opened new horizons for finding molecules in other parasites use to track their hosts. If urocanic acid is also been used by certain other worms, it can be a cost-effective preventive therapy in hosts of the developing countries.
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|Author:||Kausar, Asma; Sajid, Muhammad Sohail|
|Date:||Aug 12, 2012|
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