Bats in Mango and Litchi Trees Heighten Nipah Virus Concern

 The Nipah virus is a newly identified member of the paramyxovirus family. It was first identified in Malaysia around 1998 near the Nipah Sungai River, from which it derives its name. This virus has the potential to cause a pandemic in humans as it can infect a wide range of hosts such as pigs, humans, and fruit-eating bats. Fruit-eating bats were identified as the source of this virus.

This virus is found in date palm growing areas of India, Malaysia, and Bangladesh. Symptoms typically appear around 3 weeks after infection. Symptoms are vague yet fatal. Symptoms such as fever, headache, encephalitis, and respiratory illness, diagnosis can be challenging unless the infection occurs in Nipah-endemic regions. Infected individuals often progress to a coma state followed by death.

NiV strains in Bangladesh and India differ from those in Malaysia, contributing to distinct epidemiological characteristics of the virus. Mortality rates are higher in India and Bangladesh compared to Malaysia.

Fruit-eating bats primarily feed on date palm trees. The infected raw date palm sap is the most common form of transmission of infection from bats to humans, as outbreaks coincide with the sap harvesting season. Bats may also contaminate the sap collection utensils with their excreta. Domestic animals may also serve as a route of transmission from bats to humans.

In India, major outbreaks occurred in areas near Bangladesh's Nipah belt, including Siliguri in West Bengal and Nadia district.

In 2018, there was an outbreak of NiV in the Kozhikode and Malappuram districts of Kerala, a southern state on the west coast. This region is geographically distant from Bangladesh or West Bengal, where date palm sap consumption is uncommon. Here, the outbreaks occurred through secondary transmission, mainly human-to-human transmission. 

The concern regarding Nipah virus infection in communities has escalated following recent findings indicating that bats inhabit date palm trees and mango and litchi trees. There is a potential risk of infection for individuals who consume such fruits.

Headlines across Indian newspapers attribute the primary cause of death for seven children in Malda district, West Bengal. This outbreak was first reported in China and Vietnam.

Treatment is usually supportive or symptomatic. Patients with severe pneumonia and acute respiratory failure must be supported by mechanical ventilation. Treatment with antiviral Ribavirin is controversial as it was found to be effective against patients infected in Malaysia but had no effect on infected patients from India. Nipah viral infection can be controlled by preventing contamination of date palm sap and creating awareness of the risk of date palm sap consumption and consumption of fallen fruits eaten by birds by humans. Person-to-person transmission can be controlled by isolating the infected person, following good sanitation and hygiene, and by contact tracing of the infected individual. Healthcare workers should take extra precautions due to the risk of exposure.

https://pubmed.ncbi.nlm.nih.gov/23092599/

The economic Times

"Why Dengue Vaccine Prioritizes Previously Infected Individuals: Understanding Risks and Strategy"

CYD-TDV, the first licensed dengue vaccine, is a live recombinant tetravalent vaccine administered in three doses at six-month intervals. It's recommended for individuals aged 9–45 years or 9–60 years in dengue-endemic regions. However, only those individuals with previous exposure should receive the vaccine, therefore, pre-vaccination screening for previous dengue infection is essential (source: WHO).

One crucial consideration is that the dengue vaccine should not be given to children and adults, who have not had a previous dengue infection because it may increase the risk of severe dengue and hospitalization if infected afterwards.

For effective vaccination, children/adults, require three doses of the dengue vaccine. The second dose should be administered six months after the first, and the third dose six months after the second. This schedule ensures optimal protection against dengue. The dengue vaccine can be given alongside other vaccines, without interrupting other usual vaccination schedules. However, it is not recommended for travellers.

The dengue virus is a single-stranded positive sense RN virus, with four serotypes dengue virus 1 (DEN-1), dengue virus 2 (DEN-2), dengue virus 3 (DEN-3), and dengue virus 4 (DEN-4). Clinical manifestations of dengue can be categorized into two types: dengue fever, predominantly observed in adults during primary infection with the virus, and dengue hemorrhagic fever(DHF), which can potentially progress to dengue shock syndrome (DSS) if infected secondarily.

A secondary DENV infection results when a person previously infected with one serotype is exposed to a different serotype, and is the single most important risk factor for severe dengue disease.

Severe clinical manifestations of DHF/DSS are more prevalent in infants and there is an approximately fourfold higher mortality rate compared to other age groups. Infants born to dengue-immune mothers, if infected for the first time, may lead to severe DHF/DSS. The reason is, that the person infected with one serotype develops immunity against that specific serotype and if the same person is later infected with a different serotype of dengue virus, particularly within a relatively short time, the immune response can work against them leading to complications. Severe disease in dengue virus infections, known as severe dengue or dengue hemorrhagic fever (DHF), after secondary infection with Dengue, is associated with a phenomenon called "antibody-dependent enhancement" (ADE). 

Antibody-dependent enhancement (ADE) occurs when antibodies generated in response to the first infection recognize and bind to the new serotype of the dengue virus. Still, instead of neutralizing it, they facilitate its entry into cells via Fc receptors on immune cells. This can lead to increased viral replication and more severe disease outcomes.              

             

Severe dengue can manifest as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS), characterized by severe bleeding, plasma leakage, and organ impairment. These complications are more likely to occur in secondary infections with a different dengue serotype due to ADE.

Due to all these reasons, developing a safe vaccine against dengue has always been challenging. 

As primary dengue virus infection does not give long-term protection to re-infection with the other three viral serotypes. This is against the general rule that a vaccine will need to induce protective responses against all four serotypes.

If the individual previously uninfected with the dengue virus gets vaccinated, the subsequent natural infection with Dengue may develop into complications, possibly by ADE, as they have been primed but not protected by the dengue vaccine.

Dengue Vaccine trials have shown better efficacy in individuals who had previously been infected with the dengue virus, implying that the vaccine can boost pre-existing dengue virus immunity but is poor at producing a protective immune response in uninfected but vaccinated individuals.

The challenge lies in developing vaccines that can stimulate the immune system to produce antibodies and cellular responses effective against each serotype without causing immune enhancement, leading to more severe disease upon subsequent infections. Achieving durable protection against all four serotypes is crucial for the success of dengue vaccines, particularly in regions where multiple serotypes co-circulate and contribute to the burden of dengue fever. Therefore, extensive research and testing are required to ensure that candidate vaccines meet these complex requirements before they can be widely implemented in endemic populations.

Precautions for Vaccinating Immunocompromised Individuals

Vaccination serves critical purposes in public health, including disease prevention, immunotherapy for conditions like cancer, and efforts to eradicate diseases such as smallpox. It also controls disease transmission by achieving high vaccination rates and protecting vulnerable individuals who cannot be vaccinated. These efforts contribute significantly to global health by reducing illness, saving lives, and fostering healthier communities. 

Immunosuppressed individuals face unique challenges regarding vaccination compared to immunocompetent individuals. Due to their compromised immune systems, they may not respond as effectively to vaccines and are at higher risk for vaccine-preventable diseases.

Individuals with immunological challenges can generally be categorized into two main groups: the immunosuppressed and the immunocompromised. Immunosuppressed individuals have intentionally suppressed immune systems, often due to medications like corticosteroids or chemotherapy, or following organ transplantation. On the other hand, immunocompromised individuals have weakened immune systems due to conditions such as HIV/AIDS, genetic disorders affecting immune function, or certain cancers.

The decision to vaccinate immunosuppressed individuals requires careful consideration of their specific medical condition, the type of vaccine, potential risks, and benefits. Consulting with a healthcare provider specializing in immunocompromised conditions is crucial to determine the appropriateness and timing of vaccinations for these individuals.

A vaccine is a biological substance(antigen) that stimulates the immune system by introducing a weakened or inactive pathogen to the body, training the immune system to recognize and fight the disease in the future. They are basically divided into two types: inactivated and live attenuated. Inactivated vaccines are made from microorganisms (viruses, bacteria, etc.) that have been killed by physical or chemical methods, rendering them unable to cause disease.

Immunocompromised as well as immunocompetent individuals residing with immunocompromised patients can safely receive inactivated vaccines. Inactivated vaccines do not contain live pathogens and thus do not pose a threat of causing illness in immunocompromised individuals. This precaution ensures that they minimize the risk of transmitting vaccine-preventable diseases to vulnerable individuals. 

Live attenuated vaccines are made from disease-causing viruses (Wild type) or bacteria that have been weakened in a controlled environment. Live attenuated vaccines replicate in the host but do not cause severe disease like the wild-type organism. They stimulate immunity similarly to natural infections and, therefore, can cause mild symptoms similar to the natural disease. This poses a risk for immunocompromised individuals whose weakened immune systems may struggle to control even weakened pathogens. In such Individuals, even the attenuated antigens ( bacteria or viruses) can replicate and produce symptoms due to their weak immune conditions. 

For instance, in cases of persistent infections such as tuberculosis, administration of the BCG vaccine can result in complications such as localized lymphadenitis or even disseminated infections. Another issue involves the potential contamination of vaccines produced in tissue cultures; if these cultures are contaminated, vaccines may harbour other viruses such as retroviruses, as observed in historical instances involving the measles vaccine.

Similarly, due to safety considerations, live attenuated vaccines (LAVs) are typically avoided during pregnancy to prevent any potential risks to the developing fetus. These precautions are crucial in ensuring vaccines are safe and effective for all individuals, especially those with compromised immune systems or during sensitive periods like pregnancy.

Vaccination recommendations for immunocompromised individuals depend on their specific health conditions and medical guidance. Adjustments to vaccination schedules may be necessary to ensure optimal protection without compromising health. Generally, live vaccines should be administered at least four weeks before starting immunosuppressive therapy and avoided within two weeks before initiation. Inactivated vaccines should ideally be given at least two weeks before immunosuppression. Additionally, immunocompetent individuals who reside with immunocompromised persons should seek advice from healthcare professionals before receiving vaccinations. 

Therefore, individuals with compromised immune systems should be mindful of these guidelines before undergoing any vaccinations.

Unlocking the Mysteries of Immunity in an Ageing Population

In the elderly, there is a higher incidence of tuberculosis, pneumonia, urinary tract infections, and septicemia (bacterial infections in the bloodstream). Infections such as influenza, rhinovirus, and cytomegalovirus (CMV) are also more frequent, leading to increased sickness and death. These trends are linked to immunosenescence and other related factors.

As people age, their immune system weakens, known as immunosenescence. T-cell function and antibody effectiveness decline, reducing response to vaccines. Changes in neural and hormonal systems also affect immune function. This leads to more infections, higher morbidity and mortality rates, and increased risk of cancer.

As people age, fewer progenitor cells are produced in the bone marrow and thymus, crucial for immune cell production. The thymus starts to shrink after puberty, reducing its output of mature T cells. In older adults, T cells show increased expression of Fas and FasL proteins, including soluble FasL in the bloodstream. This may contribute to higher rates of activation-induced cell death and apoptosis, leading to lower lymphocyte counts observed in the elderly.

Macrophages, neutrophils, and NK cells are key parts of the innate immune system, active from birth throughout life, though they undergo some changes with age. Neutrophils in older individuals may develop phagocytic defects.

Phagocytic defects refer to impairments in the ability of cells such as neutrophils to engulf and digest pathogens or foreign particles effectively. This process, known as phagocytosis, is crucial for the immune system to eliminate microbes and debris from the body. When neutrophils have phagocytic defects, they are less capable of efficiently clearing pathogens like Staphylococcus aureus, increasing susceptibility to infections. This phenomenon is particularly notable in aged individuals, where such defects can contribute to compromised immune responses and higher vulnerability to certain microbial infections.

In older individuals, NK cell numbers and function remain mostly intact, although levels of certain cytokines may decrease. Cytokines are signalling molecules produced by immune cells. They regulate inflammation, coordinate immune responses, and facilitate communication between cells to combat infections and maintain overall immune function.

As individuals age, significant changes occur in their immune system, particularly in T cell populations. There is a notable increase in memory T cells but a decrease in naïve T cells. This shift suggests that while the body retains a memory of past infections, its ability to mount robust responses to new pathogens or vaccines may diminish. Furthermore, the overall numbers of T cells, including both CD4+ and CD8+ subsets, decline with age. This reduction in T cell diversity and quantity can lead to decreased immune function and heightened vulnerability to infections. These age-related changes in the immune system, characterized by altered T cell dynamics, underscore the importance of understanding immune ageing to develop strategies that can bolster immunity in older adults and mitigate age-related susceptibility to diseases.

As people age, the diversity of T cell receptors decreases. This reduction is more prominent in CD8+ T cells compared to CD4+ T cells. Additionally, T-cell responses to both mitogens and antigens diminish with age. This decline is caused by various internal and external factors, such as defects in presenting antigens, signalling pathways, and cytokine production.

Genes involved in immune response, particularly HLA genes, play a crucial role in enabling the immune system to effectively combat infections. Various HLA haplotypes can influence mortality rates and lifespan. Immunosenescence is further complicated by ageing of the endocrine and nervous systems. This includes not only declining immune function but also changes associated with ageing of neural and endocrine systems, as well as their interactions.

The result of these factors is a compromised immune system in elderly individuals. This manifests as a reduced ability to fight microbial infections effectively, leading to higher susceptibility to diseases such as tuberculosis, pneumonia, urinary tract infections, septicemia, influenza, rhinovirus, and cytomegalovirus. Additionally, the ageing of the neural and endocrine systems further contributes to immune system decline, impacting overall health and potentially increasing mortality rates among the elderly.

 Source: Roit Immunology

 

 

Uganda's Ebola Victory: A Triumph Against Ebola virus disease Re-emergence ?

Uganda declared the end of the Ebola outbreak caused by the Sudan ebolavirus on 11 January 2023. This declaration came after 42 consecutive days without any reported cases following the release of the last patient from care. As of now, there have been no recent incidents of Ebola reported.

The Ebola virus is re-emerging, posing a significant threat due to its high fatality rate, which averages around 50% and can reach up to 90%. While it's endemic to African nations, its broad transmission methods mean it can quickly escalate from outbreaks to epidemics or even pandemics, especially in our interconnected world.

To tackle this threat effectively, are we prepared with effective antivirals, safe vaccines, and widespread public awareness about the virus?

Ebola virus causes rare but fatal lethal hemorrhagic fever. This viral infection is not limited to humans but also causes diseases in nonhuman primates (monkeys, chimpanzees).

The Ebola virus first emerged in 1976 during separate hemorrhagic fever outbreaks in Yambuku, Zaire (now Democratic Republic of Congo), and Nzara, Sudan, approximately 800km apart. The virus was isolated from a patient in Yambuku and named after the nearby Ebola River to prevent stigmatization of the town. Initially believed to be related, subsequent research confirmed they were caused by distinct strains: Ebola Zaire and Ebola Sudan, named after their respective countries of discovery.

Ebola has history of re-emergence. 

Since its discovery in 1976, Ebola has caused sporadic outbreaks primarily in Central and West Africa. The first outbreak occurred near the Ebola River, spanning what is now the Democratic Republic of Congo and South Sudan. Subsequent years saw smaller outbreaks in Central Africa, affecting countries like Sudan, DRC, Gabon, and Uganda. The largest outbreak in history occurred from 2013 to 2016 in West Africa, primarily in Guinea, Liberia, and Sierra Leone, resulting in over 28,000 cases and 11,000 deaths. Smaller outbreaks continued in subsequent years, including in the DRC in 2018 and 2018-2020 and in Guinea during 2021-2022. Efforts to contain Ebola have involved international organizations and national health agencies, facing challenges due to the virus's high mortality rate and difficulties in diagnosis and treatment.
The virus belongs to the Filoviridae family, Ebolavirus genus, which includes Zaire ebolavirus (EBOV), Reston ebolavirus (RESTV), Bundibugyo ebolavirus (BDBV), Taï Forest ebolavirus (TAFV), Sudan ebolavirus (SUDV), and Bombali ebolavirus (BOMV). EBOV, responsible for Ebola hemorrhagic fever (EHF), exhibits the highest human mortality rates, followed by SUDV and BDBV. TAFV has caused only two nonlethal human infections to date, while RESTV leads to asymptomatic human infections, primarily identified in the Philippines.
 
Fruit bats of the Pteropodidae family, including Hypsignathus monstrous, Epomops franqueti, and Myonycteris torquata, serve as natural hosts of the Ebola virus (EBOV) in Africa. Nonhuman primates can contract the virus by consuming partially eaten fruits and subsequently transmit it to humans. The virus is typically introduced into human populations in endemic African regions by handling infected animal carcasses, commonly referred to as bushmeat. Subsequent human-to-human transmission then becomes a prominent feature of any epidemic. Intimate physical contact with patients in acute disease stages and exposure to blood/fluids from deceased individuals are primary transmission modes. Traditional funeral practices in African countries involve the direct handling of bodies, significantly contributing to disease spread.

EBOV RNA can persist for up to a month in rectal, conjunctival, and vaginal discharges, and up to three months in semen, indicating the virus may persist in recovering patients.
A case of sexually transmitted EVD has been reported between a convalescent patient and a close family member.

Asymptomatic carriers of EBOV are not infectious and do not play a significant role in Ebola virus disease outbreaks. Patients can only spread the infection when they have symptoms; transmission does not occur during the incubation period.

EBOV has been detected in blood, saliva, semen, and breast milk. RNA has been isolated from sweat, tears, stool, and on skin, vaginal, and rectal swabs. Exposure to infected bodily fluids is the main mode of transmission. Eating undercooked meat from infected animals, hospital-acquired infections, and poor sanitation, have also been reported in EVD dissemination. Transmission can also occur through contaminated materials (fomites) carrying infected bodily secretions. It's not clear if the disease can spread through the air or droplets.
 
Ebola viruses entering the human body infect immune system cells (dendritic cells, monocytes, and macrophages), endothelial and epithelial cells, hepatocytes, and fibroblasts, where they replicate actively, leading to high levels of virus in the bloodstream. The virus spreads to regional lymph nodes causing swelling, then travels through the blood to the liver and spleen, triggering an intense inflammatory response. This response, driven by inflammatory chemicals (cytokines and chemokines), disrupts vascular function, leading to disseminated intravascular coagulation and multiple organ failure.

Ebola can only spread to others after symptoms appear, typically within 8 to 10 days after contact, occasionally up to 21 days. Early symptoms are nonspecific, which complicates diagnosis.

Initial Ebola Virus Disease (EVD) symptoms are nonspecific, resembling dengue, typhoid fever, malaria, and flu. They typically appear 8–11 days post-infection and include high fever, headaches, sore throat, cough, abdominal pain, nausea, vomiting, and diarrhoea. As the disease progresses, symptoms worsen with bleeding manifestations such as gum and nosebleeds, gastrointestinal bleeding, and hematuria. Severe cases can lead to dehydration, shock, multiorgan dysfunction, and death.

Reverse transcriptase polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) are the primary diagnostic tests for confirming Ebola virus disease (EVD) in laboratories.

Two licensed vaccines are available for the Ebola virus (Orthoebolavirus zairense): ERVEBO (Merck), a single-dose rVSVΔG-ZEBOV-GP vaccine approved by the FDA in the United States, and Zabdeno/Mvabea (Johnson & Johnson), a two-dose regimen of Ad26.ZEBOV and MVA-BN-Filo were used in outbreaks but were not FDA-approved in the United States.

Ebola Virus Disease (EVD) is a life-threatening condition associated with a high global mortality rate and significant chronic sequelae. Survivors often experience chronic manifestations resembling autoimmune and auto-inflammatory conditions. 

Developing antiviral medications and establishing safe and effective vaccines are crucial for preparedness in managing EBOV disease under any circumstances. Antiviral drugs can provide immediate treatment options for those infected, potentially reducing severity and mortality rates. On the other hand, vaccines play a pivotal role in prevention by priming the immune system to recognize and combat the virus before infection occurs, thus curbing transmission and preventing outbreaks mainly in endemic regions. 

These approaches are essential components of a comprehensive strategy to combat EBOV disease effectively and ensure global health security.

 
 
 
 
 
 
 
 
 

Zika Virus: Emerging Threat to Human Civilization

Zika virus (ZIKV) is a mosquito-borne virus classified within the Flaviviridae family, alongside notable members such as Japanese encephalitis (JEV), West Nile (WNV), dengue (DENV), and yellow fever (YFV) viruses. The Zika virus was initially isolated in 1947 from a rhesus macaque monkey in the Zika Forest, located on the Entebbe Peninsula, Uganda. Subsequently, it was isolated from Aedes africanus mosquitoes. Mosquitoes are the primary mode of viral transmission across various geographical regions. Originating in the Ugandan forest, the virus has spread to the Pacific Islands, Latin America, North America, and now Southeast Asia.

Zika virus (ZIKV) primarily transmits to humans through the bite of infected mosquitoes. Additionally, it can cross the placental barrier, affecting the fetus during pregnancy, and spread through sexual contact, breastfeeding, or blood transfusion.

The Zika virus primarily circulates through two transmission cycles: the sylvatic cycle, occurring in forested areas where the virus is maintained between non-human primates and arboreal mosquitoes and the urban cycle, prevalent in urban settings where the virus circulates between humans and urban mosquitoes.

Recent concern has focused on managing urban mosquitoes, specifically two species: Aedes aegypti, identified by white bands on its legs, and Aedes albopictus, known for a single long dorsal stripe and white leg bands. These mosquitoes are active during daylight hours.

Zika virus can spread through sexual contact, blood transfusion, and breastfeeding. It can also be transmitted from a pregnant woman to her fetus. The virus has been found in urine, saliva, and nasopharyngeal swabs. Direct transmission through skin or mucous membranes is uncommon due to low viral levels in the blood.
Zika virus (ZIKV) symptoms range from mild to severe. Mild cases typically resolve within 4–10 days after an incubation period. Symptoms include flu-like syndromes such as low-grade fever, rash, arthritis, conjunctivitis, headache, myalgia, edema, and vomiting. Severe cases may lead to Guillain-Barre syndrome in adults, characterized by autoimmune attacks on the peripheral nervous system causing tingling, muscle weakness, and paralysis. In infants born to infected women, ZIKV can cause microcephaly, a condition where the brain does not develop properly, resulting in a smaller-than-normal head.

Currently, there are no specific medications available for preventing or treating Zika virus (ZIKV) infection. Developing a safe and effective vaccine is crucial to stop the spread of the virus. Progress in Zika vaccine development is ongoing, using various technologies such as DNA vaccines, subunit vaccines, live-attenuated vaccines, virus-vector-based vaccines, inactivated vaccines, virus-like particles (VLPs), and mRNA-based vaccines.
Before a safe and effective vaccine becomes available, the primary strategy to prevent Zika virus infection is vector control, which focuses on reducing mosquito populations, eliminating breeding sites, and avoiding mosquito bites. These measures are also effective in preventing Dengue and Chikungunya infections.

Reasons for the Increasing Frequency of Viral Diseases Emergence

Several global trends have significantly increased the risks associated with the emergence and spread of infectious diseases. Urbanization and population growth have transformed our cities into densely populated hubs where diseases can easily spread. Moreover, advancements in transportation have made global travel faster and more accessible than ever before, reducing the time it takes to circumnavigate the globe from months to just hours. This rapid movement of people means that viruses can potentially travel across continents within the incubation period of an infection before symptoms even manifest.

The SARS pandemic of 2002–2003 serves as a stark example of how quickly a new virus can spread globally. Originating in China, SARS-CoV spread to more than two dozen countries within a matter of months, highlighting the interconnectedness of our modern world and the challenges it poses for disease control and prevention.

In addition to human activities, environmental changes driven by agriculture and urban development play a crucial role in disease emergence. The conversion of natural habitats for agriculture or infrastructure projects creates new ecological niches that can harbour disease vectors and reservoirs. For instance, urban yellow fever likely originated when humans entered jungle areas where the virus was maintained in a cycle between monkeys and mosquitoes. The introduction of infected individuals back into urban centres facilitated the virus's adaptation to a new cycle involving mosquitoes like Aedes aegypti, which thrive in urban environments and preferentially feed on humans.

Furthermore, the intensification of agribusiness has led to the concentration of large numbers of livestock or crops in confined spaces. This practice increases the risk of rapid disease transmission among closely packed animals or plants, creating conditions ripe for the emergence of new pathogens or the spread of existing ones.

International trade in plants and animals has also contributed to the spread of diseases across borders. The 2003 outbreak of monkeypox in the United States, for example, was traced back to the importation of Gambian giant rats from Africa as exotic pets. The virus spread from these animals to domestic pets and then to humans, causing public health concerns due to its similarity to smallpox.

These interconnected factors underscore the urgent need for global cooperation and proactive measures to monitor, prevent, and respond to emerging infectious diseases. As our world becomes increasingly interconnected and urbanized, understanding and mitigating the risks posed by infectious diseases have become critical global health priorities.

In the mid-1800s, rabbits brought from Europe to Australia for sport quickly multiplied without natural predators, threatening grasslands and crops in southern Australia. To control their numbers, the myxomatosis virus was introduced in 1950, causing a devastating outbreak among the rabbit population due to its high lethality. Over time, the virus evolved, with less deadly strains becoming more common as rabbits developed genetic resistance. This natural selection favoured moderately harmful strains because milder ones struggled to spread, while highly lethal ones killed rabbits too quickly to transmit effectively.

This situation demonstrates the complexities of using viruses for population control and raises concerns about unintended consequences. Introducing viruses, even for beneficial purposes like managing wildlife, can disrupt ecosystems and pose biosecurity risks. Such considerations are crucial in both wildlife management and assessing the potential risks associated with intentional virus introductions, which could also serve as models for bioterrorism.

Significant progress has been made in the field of xenotransplantation, particularly in using genetically modified pigs as organ donors to address the shortage of human organs for transplantation. Research has focused on various areas such as pancreatic islets, neuronal cells, corneas, and vascularized organs like kidneys and hearts. However, a critical concern arises regarding the potential transmission of known or unknown latent or persistent viruses from donor organs to transplant recipients. This is especially pertinent because transplant recipients undergo immunosuppression to prevent rejection of the transplanted organ, which could make them more vulnerable to infections from viruses originating from the donor species.

In the worst-case scenario, this situation could facilitate the transmission of a foreign virus across the species barrier, allowing it to establish itself as a new human virus. Such a virus could potentially spread from the graft recipient to others, posing significant public health risks. Therefore, while xenotransplantation offers promising solutions to organ shortages, careful consideration and ongoing research are essential to mitigate the risks associated with viral transmission and ensure the safety of transplant recipients and the broader community.