Why do diseases re emerge

Seek information as far before traveling as possible, even if the destination is one you have previously visited. Health conditions can change quickly in certain areas of the world.

Get as much information as possible about current health risks for the country or countries you are visiting and learn about special risks for children, pregnant women, people with chronic diseases, and people with weakened immune systems who might be traveling with you.

For specific recommendations, see a travel medicine specialist or a healthcare provider familiar with the area you will be visiting at least 4 to 6 weeks before your trip. If you are pregnant or plan to become pregnant, make certain to ask a travel medicine specialist about any pregnancy-specific concerns in your travel area. Get the immunizations and take the preventive medicines recommended by your healthcare provider. Since some of these must be given or taken weeks before travel, contact your healthcare provider as early as possible to make sure that the effectiveness of these measures.

If medicine is needed for prevention of malaria, be sure to take it as prescribed. Follow dosage instructions carefully.

Malaria preventive medicines must be started before your trip to make sure that protective levels in your body before any exposure to mosquitos at your destination.

Check with your healthcare provider or pharmacist to be sure you begin them early enough. They must be continued throughout your trip and for a specific number of days after you return. The amount of time depends on which medicine you are prescribed. Put together a traveler's first aid kit with specific items geared to your destinations. Add enough extra medicines and supplies to last a few days past the duration of your trip. Your healthcare provider can help you identify what should be included in your kit.

Research emergency medical care during your trip and what medical evacuation services are available in case of serious illness. Contact your health insurance plan to find out what is covered in other countries. The World Health Organization warned in its report that infectious diseases are emerging at a rate that has not been seen before.

With people traveling much more frequently and far greater distances than in the past, living in more densely populated areas, and coming into closer contact with wild animals, the potential for emerging infectious diseases to spread rapidly and cause global epidemics is a major concern. Additionally, there is the potential for diseases to emerge as a result of deliberate introduction into human, animal, or plant populations for terrorist purposes, as discussed in the section on Bioterrorism Agents.

These diseases include anthrax , smallpox , and tularemia. Some result from natural processes such as the evolution of pathogens over time, but many are a result of human behavior and practices. Consider how the interaction between the human population and our environment has changed, especially in the last century.

Factors that have contributed to these changes are population growth, migration from rural areas to cities, international air travel, poverty, wars, and destructive ecological changes due to economic development and land use. For an emerging disease to become established at least two events have to occur — 1 the infectious agent has to be introduced into a vulnerable population and 2 the agent has to have the ability to spread readily from person-to-person and cause disease.

The infection also has to be able to sustain itself within the population, that is more and more people continue to become infected. Many emerging diseases arise when infectious agents in animals are passed to humans referred to as zoonoses.

As the human population expands in number and into new geographical regions, the possibility that humans will come into close contact with animal species that are potential hosts of an infectious agent increases. When that factor is combined with increases in human density and mobility, it is easy to see that this combination poses a serious threat to human health. Climate change is increasingly becoming a concern as a factor in the emergence of infectious diseases.

As Earth's climate warms and habitats are altered, diseases can spread into new geographic areas. For example, warming temperatures allow mosquitoes - and the diseases they transmit - to expand their range into regions where they previously have not been found.

A factor that is especially important in the re-emergence of diseases is antimicrobial resistance - the acquired resistance of pathogens to antimicrobial medications such as antibiotics. Bacteria, viruses, and other microorganisms can change over time and develop a resistance to the drugs used to treat diseases caused by the pathogens. Therefore, drugs that were effective in the past are no longer useful in controlling disease. Another factor that can cause a disease to re-emerge is a decline in vaccine coverage, so that even when a safe and effective vaccine exists, a growing number of people choose not to become vaccinated.

This has been a particular problem with the measles vaccine. Measles, a highly contagious and serious infection that was eliminated from the U. The other critical problem in densely populated areas is the lack of clean water which increases the transmission of viral diseases. As WHO recommended washing our hands with clean water and other disinfectants is one of the preventive methods for COVID, but getting water in such areas might be a challenge for developing countries. Therefore, this becomes an obstacle in preventing the spreads of COVID and other viruses that can be transmitted via contact.

Migration and war which causes human population movements or upheavals are the critical factors for disease emergence [ 4 ]. Migration of humans is the best means for spreading infectious diseases and is inevitable to shape the emergence, frequency, and spread of infections in geographic areas and populations [ 34 ]. As example, in Syria millions were displaced, hundreds of thousands gone for goods and the rest were wounded.

Beyond such humanitarian crises, the civil war has opened the door for emergence of epidemic of infections that have spread through vulnerable populations in Syria and neighboring countries [ 35 ]. According to United Nations High Commissioner for Refugees [ 36 ] around 37, people a day forced to flee their homes because of conflict and persecution.

Therefore, this mass venture leads them to death, to live in refugee tent and to be infected with disease and spread the disease. During these upheavals the rate of disease transmission is paramount and refugee tents could be "disease incubation centers". An immediate and appropriate intervention measures must be taken otherwise those infected individuals could be reservoirs for the virus that can and will re-infect other populations worldwide.

Due to the current emerging virus COVID most aid providers may turn face to their internal issues; in this case migrants may face another severe intractable problem. Thus, the global communities should not forget citizens living within a camp otherwise they will go for goods or becomes a source of infection for the rest communities.

Transmission of viruses from animals to humans is tremendous for emergence or re-emergence of infectious disease. Thus, emerging or re-emerging viral infectious diseases scourges not only human health, but also animal health [ 37 ]. Viruses spread without any borders and they jump from animals to humans, and they move from one country to another country [ 20 ].

The majority of all human infectious diseases and pandemics have originated through the cross-species transmission of microorganisms from animals to humans [ 38 ].

Therefore, the recently emerging pathogens, originate from animals, and continuing disease transmission from animals to human and they became health burden [ 39 ].

This issue is more severe in agriculture practice societies because in agrarian nations there is an intimate interaction between animals and humans and animals may act as reservoirs of human diseases [ 1 , 40 ]. That is why zoonotic virus spillover from wildlife was most frequent in and around human dwellings and in agricultural fields [ 39 ].

Besides this, human settlements by itself are conducive for interspecies transmission between farm animals, rodents, dogs, cats and insects [ 40 ]. As shown on Figure 4 and Figure 5, there are numbers of zoonotic viruses that can be transmitted from animals or insects to humans. For instance, viruses that originate in bats may be the most notorious emerging zoonoses that spill over from wildlife into domestic animals and humans [ 23 ].

Thus, bats are the reservoirs for an array of emerging viruses including coronaviruses CoVs that cause serious disease in humans and agricultural animals [ 41 ]. As Figure 4 and Figure 5 revealed MERS-CoV is zoonotic virus that can be transmitted from camels to human and this virus is also actively circulates among camels and there is also human-to-human transmission [ 42 ].

Some viruses such as coronaviruses CoV are frequently shifting hosts, that can be transmitted from animal-to-human zoonosis , human-to-animal anthroponotic disease , or animal-to-animal [ 43 ]. View Figure 4. Figure 5: Examples of zoonotic viruses that can be transmitted from animals or insects to humans [ 3 , 15 , 31 , 59 ]. View Figure 5.

The other contributing factor for viral disease emergence is global or local wildlife trade which is the best means for disease transmission and outbreaks [ 45 ]. Illegal trade of bush meat is also paramount for zoonoses to be transferred to the human population. SARS-CoV which was emerged in and its outbreak was most likely linked to animal markets and history repeats itself, COVID outbreak is likely related to the seafood market with wildlife trading.

However, it is still unknown whether COVID was zoonotically transmitted from an infected civet cat, snake or other animal such as pangolin at the Huanan seafood market [ 46 ] Figure 4.

Therefore, it is highly believed that wild animals were involved in the emergence of this contagious virus [ 47 ]. Frequent interaction and mixing of different animal species in densely populated areas such as in markets and intrusion human into the natural habitats of animals; have facilitated the emergence of novel viruses [ 31 ].

Generally, wild game mammal's interaction in overcrowded cages and unhygienic wet markets allowed the jumping of novel virus from animals to human [ 48 , 49 ]. Currently around the globe people have been told to stay at home due to amid COVID but this lockdown order brings a good opportunity for wild animals to venture into urban areas and spill over the deserted roads and cities.

As reports revealed in different country roads are invaded by wild animals. This unprecedented event may bring additional health risks. During this animal roaming there might be an interaction between wild and domestic animals which will open for eruption of zoonotic diseases. Perhaps another pandemic may evolve. Therefore, readiness for the known and unknown infectious diseases will be a top priority for our public health systems [ 26 ]. For example, COVID emerged in unexpected time, without any preparedness and taking many lives and collapses the global economy.

As we are living in unpredictable, environment humans should take lesson from such kinds of horrific events and get ready for next challenges [ 50 ]. As global population is increasing from time to time, land demand is also increasing that put pressure on ecology which leads ecosystem disturbance. Intensive agricultural practice and environmental change were highly related with an increased risk of zoonotic disease emergence [ 51 ].

Intrusion of human settlements and agriculture on natural ecosystems provides new opportunities for pathogen spillover, genetic diversification, and adaptation. This zone is a critical transition zone where humans, domestic and wild animals are interacting so that zoonotic pathogens may spillover which will be local or global health threat. As Jones, et al.

As different studies revealed global or local climate change, disturbance of ecosystems and ecosystem services, large-deforestation, and urbanization as drivers of a wide range of life-threatening infectious diseases [ 53 ].

Anthropogenic activities may devastate natural environment and this in turn open a door for emergence or re-emergence of infectious diseases. Therefore, to be healthy, the general wellbeing of plants, animals and our environment should be healthy. This is the general principle of "one health" approach which considers the connections between the environment, plant, animal and human health [ 54 ].

Generally, exploiting the natural environments and ecological disturbance along with anthropogenic activities ushered the emergence or re-emergence of viral infectious disease. The other contributing factor in emergence or re-emergence of infectious disease is viral related factor. Pathogens may be prone to emergence in themselves, and rapidly mutating viruses are more common among the emerging pathogens [ 37 ].

RNA viruses of plants and animals possess polymerases which are error-prone and produce complex populations of related, but non-identical, genomes called quasispecies [ 56 ]. Therefore, upon any harsh environmental conditions such as antiviral stresses, host immune response and treatment of antiviral drugs RNA viruses can mutate or evolve rapidly [ 3 , 57 ]. Viruses, particularly RNA viruses, are adept at change and have several mechanisms for altering their genomes [ 15 ].

They achieve the high evolution rate through different mechanisms such as mutation, reassortment, and recombination [ 3 , 15 ]. Majority life threatening newly emerging viruses are RNA viruses [ 57 ]. For instance, mutation and adaptation have driven the co-evolution of coronaviruses CoVs [ 58 ]. Pathogenic RNA viruses are potentially the most important group involved in disease transmission from animal to human, and they represent a challenge for global disease control [ 59 ].

Generally, a distinctive feature of RNA genomes is the error-prone nature of their replication and retro-transcription [ 60 ]. As reports revealed in Chinese wet-markets are potential epicenters for transmission of viral pathogens and new genes might be acquired or existing genes modified through various mechanisms such as genetic reassortment, recombination and mutation [ 49 ].

This property of RNA viruses makes them to be a potential pathogen that threatens public health and causes economic recession.

For instance, our globe is threatened by COVID and perhaps who knows another novel new coronavirus may evolve in unexpected time. In human evolution, viruses are serious infectious agents causing a number of life-threatening diseases [ 3 ]. Therefore, most of the deadly epidemic and pandemic disease in human history is caused by viral pathogens [ 13 ]. Among an innumerable number of viruses, coronaviruses are the hottest issue that scourge human life globally.

In the early s, they have been identified and linked to human cattle, pig, and chicken diseases [ 61 ]. And again in , another dangerous disease called Middle East respiratory syndrome was emerged and was caused by novel coronavirus called Middle East respiratory syndrome coronavirus MERS-CoV [ 63 ]. Now on 31st December , at Wuhan city, Hubei Province, in China new case of pneumonia of unknown etiology was detected and the World Health Organization WHO was alerted about this unprecedented etiology.

After identifying more cases from patients, then they confirmed that the infectious agent was novel coronavirus COVID [ 29 , 65 ].

The current emerged novel human coronavirus, SARS-CoV-2, has become a global health challenge causing severe respiratory tract infections in humans [ 66 ].

This deadly and contagious viral disease continues to take lives globally. We human beings are "invaded" by COVID pandemic which declares devastating "war" on us and detained us to stay at home forcibly. Therefore, it is possible to say that our globe is under viral war. Coronaviruses belong to the Coronaviridae family of the Nidovirales order [ 67 - 71 ].

Coronavirus virions are spherical overall but the RNA genome inside is arranged in a flexible helical structure, closely bound to a nucleocapsid protein [ 72 ] Figure 6.

As shown on Figure 6 RNA black color is associated with nucleoprotein orange color. Most RNA viruses are deadly pathogens since they evolve rapidly in any hostile conditions and exhibit error-prone gene replication [ 3 ]. If the virus continuously mutates, recombines or reassorts, then human health will be scourged.

This is because the virus will be emerged in unexpected time with unknown "weapons" and mysterious behavior and this in turn will be new or unknown for immune cells which are our "soldiers" and as well as medication. Therefore, understanding its obscure behavior and developing vaccines or antiviral drugs needs time, but within this time gap lives of millions will be lost. That is why we are wrestling with COVID a current global health threat and future fear of public health, because everything is on its own hand and it might be more aggressive.

Several human pathogenic viruses are enveloped possessing lipid bilayer which acts as an additional protective coat and infects their target cells by inducing the fusion of the viral envelope with the cell membrane [ 73 ]. Therefore, this lipid-containing membrane surrounds some virus particles and surfaces proteins are protrude from this membrane Figure 6.

As shown in Figure 6 Coronavirus virions contain structural proteins such as spike glycoprotein S , envelope glycoprotein E , membrane glycoproteins M , and nucleoprotein N.

Besides these structural proteins, some coronaviruses such as betacoronaviruses have the second fringe of shorter spikes called hemagglutinin which has enzymatic activities Figure 6. Therefore, they contain receptor-destroying enzymes that exhibit acetylesterase, as well as receptor-binding activity.