Jan 25, Killer viruses on the prowl, threaten human life on the viruses include Lassa fever in West Africa, especially Nigeria; Ebola Virus Disease (EVD) The Ebola outbreak, which began in Guinea in December , has killed more than 11, To date, 26 countries from all continents have reported cases. Apr 11, When the first Ebola virus victims were identified in Guinea in February, it is one of the most deadly diseases on the planet to aflict humans. and volunteers are keeping that all up to date," says Andrew Braye, All that information can now be fed in to the OSM map by digital humanitarians on the prowl. Feb 7, but malaria fever is still with us while typhoid fever remains on the prowl. Sierra Leone is still at alert for Ebola fever and Saudi Arabia is wary of The outbreak of Zika virus has led authorities in some countries to urge However, there is still no evidence of transmission Zika virus in Europe to date and.
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The cholera bacterium is more virulent to humans when infected by a particular virus. On an average a virus has about 4, bases the simple building blocks of geneswhich means that a few million permutations in their genetic arrangements are possible. Viruses either have single and double stranded dna or rna; the rates of mutation vary vastly. Size of the genome and infectivity, numbers of hosts infected and number of generations produced too affect this greatly. Thankfully, not all mutations are possible -- some of these mutations are lethal for the virus itself.
Microbial traffic The few pathogens that develop effective virulence may still not be able to invade another host because they may be too few or too "weak". This means that if a requisite inoculum size is not achieved then the host may overcome the infection and dash the virulent ambition of the pathogen.
This phenomenon is called a transmission bottleneck, which can drive down the virulence of a pathogen. Two distinct methods of transmission occur.
In vertical transmission, infections are transmitted from mother to child or vertically across generation. In horizontal transmission, infections are transmitted to all susceptible hosts in the population like in the case of the common cold and infectious fevers. According to an interesting hypothesis by Paul Ewald of Amherst College, usa, virulence of pathogens is low in vertically transmitted diseases as they depend entirely on the survival of their host.
Pathogens transmitted horizontally are more virulent and can even kill their hosts as long as they manage to move on to new victims see table: Paths of a pathogen.
According to Carl Bergstrom, professor of biology at Washington University, usa, transmission is a tight "bottleneck" for a number of diseases. He contends that similarly sized bottlenecks have greater genetic consequences on vertically transmitted pathogens than on horizontally transmitted pathogens.
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Together these transmission modes determine the evolutionary and virulent fate of the viruses. An organism, it appears, is guided by a certain pathological destiny -- either to have a short evolutionary life but have an extremely virulent form or to have a long evolutionary life but live in benign co-existence with the host.
Turf battles Pathogens too don't have it all easy. Millions of bacteria compete among themselves in an endless turf battle, jostling for space in the human gut or sweat-laden folds of the skin. It makes perfect sense that they would evolve means to survive and fight off competitors and devise means to invade the human cell more rapidly, producing near perfect replicants, which burst out of the host cell to invade new cells in a new host.
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All this must be done before a more powerful pathogen arrives and stakes claim on a host cell. But not all infections may be successful. Many unknown pathogens are widely present in the environment and are easily communicable to susceptible individuals in a population. But there are resistant individuals in the population who don't contract these infections, and their presence protects the rest. This paradoxical mechanism is called herd immunity and has been harnessed for attempts to control diseases.
If you immunise say 90 per cent of the schoolchildren against measles, then the measles virus can no longer spread because there are too few susceptible children in the population. The immunised majority protects the un-immunised minority.
But if you let your guard down for a moment, and the immunisation rate drops below 90 per cent, then the virus that has been hiding somewhere, reappears and there is a measles outbreak. The phenomenon may apply to naturally occurring immunity as well. A season of fevers Most diseases have an ecological basis to their origin.
Seasons and changing climate too assist the emergence of diseases. In poor states like Bihar and Orissa there is a distinct 'microbial traffic', a virtual succession of infectious microbes. Even causalities have a pattern: During the rainy season, malaria and fevers of unknown origins emerge, all age groups are affected but the effect on young women and pregnant women is more.
If a natural calamity like flood or cyclone arrives, then malaria recurs, and cholera and other gastro-intestinal infections follow which affect young adolescents and children more than adults. In winter the paucity of food causes widespread hunger and leads to malnutrition, makes people more susceptible to infections, thereby providing an ideal environment for the spread of diseases. There are distinct patterns of succession of diseases with changing seasons. In cities of north India, when the winters end abruptly, a spate of viral infections descends on the cities and the villages alike.
There is little climate variability in the rest of the country except the coming of the monsoon. Winters are milder and summers like the rest of the country is hot. Forest and rural areas in India have their fair share of viral diseases.
Kyasanur forest disease seen in Uttara Kannara and Shimoga districts of Karnataka is a tick borne fever that causes fever and body ache. Recently, the viral meningitis in Bellary claimed a dozen lives.
Its origins and causes remain unknown. Threats from ecological changes in neighbouring countries leads to migration. For example, rural families from eastern Nepal migrate to the forests and the plains of upper Assam every year. With them they bring their livestock, especially buffaloes, each infected by a benign virus called the Karyovirus-II. When these families settle around the forest fringes, a chance encounter with a new vector increases the possiblities of its spread to humans.
The fever causes severe haemorrhagic fever, bleeding and death. Like the Karyovirus of Nepal, there are many fevers -- Crimean Congo Haemorrhagic fever in Pakistan and the numerous diarrhoeal diseases in Bangladesh -- waiting to nurture their virulent ambition in India. Human trigger What is more significant in disease ecology is not how mutated viruses and other pathogens become established in humans, but how ecological change contributes to its emergence.
Causal factors -- changes in land use, human activities and urbanisation -- are integrated with ecological factors to cause mutation, changes in the pool of hosts and reservoirs and other elements. These in turn affect both human and animal hosts, as well as vectors.
Moreover, air, water or soil pollutants or other stresses affect humans and other species in the ecosystem. Polluted habitats are an ideal environment for these pathogens.
Pollution reduces human immunity. And some pollutants can promote the growth and proliferation of some pathogens. Microcephaly and other brain deformities in newborns have also been reported, particularly in Brazil. With no vaccine, or specific treatment, Zika has become a potential death sentence overnight.
The Zika virus itself is considered a bit of a dark horse by scientists. The vector Like dengue fever and chikungunya, two similar diseases, Zika is transmitted by the aedes mosquito species found in tropical and sub-tropical regions. Today, Zika virus is considered an emerging infectious disease with the potential to spread to new areas where the aedes mosquito vector is present. However, there is still no evidence of transmission Zika virus in Europe to date and imported cases are rare.
It is a known vector of several viruses including yellow fever virus, dengue virus and chikungunya virus.Monkey Meat and the Ebola Outbreak in Liberia
Others are Japanese encephalitis, viral haemorrhagic fevers and Zika virus. Over the past 25 years there has been an increase in distribution of this mosquito to every continent worldwide making it one of the most widespread mosquito species globally. The success of this invasive species has largely been due to globalisation. It thrives in densely populated areas which lack reliable water supplies, waste management and sanitation. Historically, this mosquito has moved from continent to continent via ships, and this method of dispersal is thought to present the highest risk.
It is even suggested that the mosquito evolved its domestic behaviour in West Africa and its widespread distribution and colonisation in the tropics led to the highly efficient inter-human transmission of viruses such as dengue. But as they have adapted to more urban domestic habitats, they have exploited a wide range of artificial containers such as vases, water tanks and tyres that are often associated with human habitations.
The mosquito has also been found utilising underground aquatic habitats such as septic tanks and adapting to use both indoor and outdoor aquatic habitats in the same area. Adaptation to breeding outdoors may allow for increased population numbers and difficulty in implementation of control methods. The insect is often not found further than m from human habitations. They prefer human habitations that provide resting and host-seeking possibilities and, as a result, will readily enter buildings.
Hope for a vaccine How far away is a Zika virus vaccine? Experts say research efforts will focus on developing a vaccine for the mosquito-borne illness, but it will take time.
Two potential approaches have been mapped out to developing a Zika vaccine. The second, more traditional approach would use a live attenuated vaccine in which the virus has been weakened to prompt immunity.
The new test can, therefore, definitely determine if a person is a carrier of the Zika virus, as only one in five people infected actually becomes ill, the media reports. Additionally, the test renders diagnostic results in real time, which is relatively quick for a virus of this kind. The test examines DNA and works with chemicals that react to the Zika virus only.
Scientists from around the world have pledged to fast-track the research.
However, despite technological advancements, scientists confessed that there are many challenges to the development of a vaccine.
The target profile is women who are pregnant or who are planning to get pregnant — which is about the highest bar there is for safety. But the vaccine will also need to undergo further animal trials, which could take some time.