Understanding Zika Virus: Prevention and Community Responsibility

The Zika virus, primarily spread by the Aedes mosquito, is a public health concern requiring collective action. Although it was first identified in the 1940s, its recent outbreaks have highlighted the urgent need for awareness and prevention, especially among vulnerable populations such as pregnant women.

How Zika Virus Spreads

Zika is transmitted through the bites of infected Aedes mosquitoes, which also spread Dengue, Chikungunya, and Yellow Fever. These mosquitoes thrive in stagnant water, breeding in flower pots, old tyres, and gutters. They have a short life cycle of about 7 to 10 days, but their eggs can survive drought conditions for over a year, hatching when exposed to water. This resilience means that effective control strategies must focus on eliminating breeding sites and raising community awareness.

 Preventive Measures

Preventing Zika requires a dual approach: individual responsibility and community cooperation. Here are some key strategies:

1. Eliminate Breeding Grounds: Regularly check your surroundings for standing water and dispose of items that can collect rainwater. Encourage your neighbours to do the same.

 2. Insecticide Use: Spraying insecticides can be effective, particularly during the mosquitoes' peak activity times—early morning and dusk. It’s essential to inform residents a day ahead so they can prepare by closing windows and doors.

 3. Personal Protection: Individuals, especially pregnant women, should use mosquito repellents containing DEET, IR3535, or Icaridina. Wearing long sleeves and pants can also provide an extra layer of protection.

 4. Community Engagement: Everyone has a role in keeping public areas clean. Local officials, businesses, and NGOs should collaborate on community cleanup campaigns and educational outreach.

 5. Pregnancy Precautions: Pregnant women should take extra care to avoid mosquito bites, attend all prenatal appointments, and consult healthcare providers promptly if they experience symptoms such as fever, rash, or joint pain.

Symptoms and Healthcare Guidance

 Many people infected with Zika show no symptoms; however, those who do often experience mild symptoms like rash, fever, and joint pain. If you suspect you've been exposed to Zika or experience any symptoms, seek medical attention immediately. Since there’s no vaccine available, the focus remains on symptom management and mosquito control.

 The Importance of Communication

 In the face of uncertainty regarding Zika, transparent and timely communication is vital. Public health authorities should provide clear, accurate information about the virus and prevention strategies. Utilizing multiple channels—social media, community leaders, and local news—ensures that everyone receives consistent messages. Coordination among health organizations is crucial to maintaining public trust. By providing updates, addressing concerns, and avoiding conflicting messages, communities can better mobilize against the spread of Zika.

 Conclusion

The Zika virus poses a risk to everyone, but by working together, we can effectively reduce transmission and protect our communities. Every individual’s efforts matter—from eliminating breeding sites to using repellents and staying informed. By promoting collective responsibility and sharing accurate information, we can safeguard the health of our families and neighbours, especially those who are pregnant or planning to conceive. Let’s commit to a proactive approach to combating Zika. Together, we can make our environments safer and healthier for all.

"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.

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.

Immune Amnesia Associated with Measles

 The immune responses triggered by measles virus (MV) infection can unexpectedly suppress the body's ability to respond to other unrelated antigens, a condition that may persist for weeks to years after the acute illness subsides. This immune suppression significantly increases vulnerability to secondary bacterial and viral infections such as pneumonia and diarrhea, which are major causes of illness and death following measles.

Measles infection disrupts delayed-type hypersensitivity (DTH) responses to known antigens like tuberculin, and impairs both cellular and humoral responses to new antigens. This immune dysregulation also contributes to the reactivation of tuberculosis and the worsening of autoimmune diseases post-measles.

In essence, measles-induced immune suppression not only weakens immediate defenses against pathogens but also compromises the immune system's ability to mount effective responses to a range of antigens over an extended period.

Measles-induced immune suppression can occur due to changes in antigen-presenting cells or effector lymphocytes, or through the depletion of CD150+ memory lymphocytes. Measles virus (MV) infects CD150+ immune cells, including memory T- and B-lymphocytes. Studies comparing blood samples collected from unvaccinated children before and after measles reveal incomplete reformation of B-lymphocyte pools post-infection. Additionally, measles leads to a significant reduction in circulating antibodies against various viruses and bacteria, impairing immunological memory and causing what is termed 'immune amnesia'.

This mechanism contributes to increased childhood morbidity and mortality for more than two years after measles infection. Abnormalities in both innate and adaptive immune responses are evident following MV infection. Children commonly experience transient lymphopenia, characterized by decreased T and B lymphocytes in the blood. Furthermore, immune cells such as dendritic cells, crucial for presenting antigens to lymphocytes, show impaired maturation and reduced ability to stimulate lymphocyte proliferation.

In summary, measles disrupts immune function by compromising both cellular and antibody-mediated immunity, leading to prolonged susceptibility to infections and contributing to the severity of measles-related complications in children.

Antiviral Drug Resistance: A Global Problem

 RNA viruses, renowned for their high mutation rates, undergo rapid evolution. Consequently, genotypes harbouring mutations conferring drug resistance can emerge swiftly. A virus strain is deemed 'resistant' to a drug if it can replicate in the body despite the presence of the drug at concentrations that inhibit replication of 'sensitive' strains. Drug-resistant virus isolates typically exhibit gene mutations encoding the proteins the drug targets. Most mutations leading to drug resistance in HIV-1 involve changes in amino acids. However, some mutations can also involve deletions or insertions of genetic material. In the HIV-1 virus, mutations in the reverse transcriptase gene that make it resistant to nucleoside analogues (such as AZT) occur in different specific codons compared to mutations that confer resistance to non-nucleoside inhibitors (like nevirapine). This difference is because these two classes of drugs target distinct regions within the reverse transcriptase enzyme. This specificity in mutation locations highlights how different drugs can influence HIV-1's genetic makeup differently, affecting its ability to resist treatment.

Clinical challenges arise when drug-resistant virus strains develop in patients undergoing treatment and when these resistant strains are transmitted to others. When drug-resistant HIV strains emerge during treatment, patients may switch to alternative medications. Initially, AZT was widely used for HIV treatment but resistance quickly developed. Similar challenges arose with other single-drug therapies. The current standard for treating HIV infection involves highly active antiretroviral therapy (HAART), which combines different classes of drugs like reverse transcriptase inhibitors and protease inhibitors.

Monitoring the effectiveness of HIV treatment involves measuring HIV RNA levels in the blood. HAART typically leads to a rapid reduction in HIV RNA within the first 10 days, followed by a slower decline over weeks. In some patients, HIV RNA stabilizes at low levels (5-50 copies/ml), while in others, it drops to less than 5 copies/ml over time.

HAART also reduces HIV levels in the seminal fluid of men and the genital secretions of women. While it doesn't eradicate HIV from the body, the virus persists in latent forms in macrophages, memory CD4 T cells, and possibly in immune-privileged sites like the brain and testes. Despite this persistence, HAART has significantly lowered AIDS-related mortality in developed countries. Additionally, treating HIV-positive women has substantially decreased mother-to-child transmission risks.

Overall, HAART represents a pivotal advancement in managing HIV infection, offering optimism through effective suppression of the virus and improved quality of life for patients.

Can all types of vaccines be given on the same date?

Administration of different vaccines at the same visit both live and inactivated vaccines does not result in decreased antibody responses or increased rates of adverse reaction. Simultaneous administration of all vaccines for which a child is eligible is very important in childhood vaccination programs because it increases the probability that a child will be fully immunized at the appropriate age.

For some vaccines, administration should not be done at different time intervals. The live parenteral (injected) vaccines (MMR, MMRV, varicella, zoster, and yellow fever) and live intranasal influenza vaccine (LAIV should be separated by at least 4 weeks. This interval is intended to reduce or eliminate interference from the vaccine. The yellow fever vaccine Should be administered less than 4 weeks after the single-antigen measles vaccine. A 1999 study demonstrated that the yellow fever vaccine is not affected by the measles vaccine given 1–27 days earlier. Live vaccines administered by the oral route (oral polio vaccine [OPV] oral typhoid, and rotavirus) are not believed to interfere with each other if not given simultaneously. These vaccines may be given at any time before or after each other. The Rotavirus vaccine is not approved for children older than 32 weeks, and oral typhoid is not approved for children younger than 6 years of age.

Parenteral live vaccines (MMR, MMRV, varicella, zoster, and yellow fever) and LAIV are not believed to have an effect on live vaccines given by the oral route (OPV, oral typhoid, and rotavirus). Live oral vaccines may be given at any time before or after live parenteral vaccines or LAIV. All other combinations of two inactivated vaccines, or live and inactivated vaccines, may be given at any time before or after each other.

 

HIV as the emerging infectious Viral disease

 “Infections that have newly appeared in a population or have existed previously but are rapidly increasing in incidence or geographic range” is termed as Emerging infections (EIs). In 1981, a new disease — acquired immune deficiency syndrome (AIDS)was first recognized. The emergence of HIV raised few questions, firstly the zoonotic source of HIV and its inter and intra species transmission.
Simian immunodeficiency virus (SIV)may have transmitted to humans in at least four separate occasions, identified by individual HIV-1 lineages called groups (M, N, O, P). The most important was the M group of HIV-1, main cause of human infections. HIV-1 is most closely related to SIVcpz, the SIV strain infecting two subpopulations of chimpanzees. Different segments of the SIVcpz genome, are closely related to genome segments of two SIVs of African monkeys, red-capped monkeys and Cercopithecus monkeys.

It is assumed that chimpanzees, regularly kills monkeys, were infected during consumption of their prey; and this infection may have led to a recombination event producing SIVcpz, which was derived from parts of the genomes of the two acquired monkey viruses. Further transmission from Chimpanzee to humans may have occurred during butchering of non-human primates mainly in rural Africa.

During the period from 1930 to 1980 the virus remained as a rare and unrecognized infection in residents of jungle villages in West Africa during this time, reuse of unsterilized needles occurred, a frequent practice during the period of colonial rule, could have helped to spread the virus. 

 

In 1980, the virus began to spread more rapidly. Accelerated spread began in the region centered on Kinshasa (previously Leopoldville) in the Democratic Republic of the Congo (previously the Belgian Congo, then Zaire) and Brazzaville, just across the Congo River in Congo. Transmission was enhanced by the chaos in postcolonial Zaire.
During the period 1985–2004, HIV infection spread widely in Africa. And the prevalence of infection among adults aged 15–49years reached levels higher than 30%. 

The rapid spread was driven by many factors ,such as a high frequency of concurrent sexual contacts in some segments of the population and the hidden nature of sexual networks., the long asymptomatic incubation period during which infected individuals able to transmit the virus were sexually active, the spread along commercial routes of travel within Africa; the failure of health systems to publicize the risks and the under utilization of condoms and other measures to reduce transmission the slow introduction of antiviral treatment after it became available in the northern countries about 1996.

With the spread of HIV in Africa, the M group of HIV-1 evolved into nine different subtypes (A–D, F–H, J, K), based on sequence diversity. Subtype C is most frequent in southern Africa, and subtypes A and D are most frequent in eastern Africa. During the 1980s, HIV spreaded globally, although prevalence rates lower than in some African countries. Subtype B is dominant in the western hemisphere and Europe, while subtype C is most frequent in India and some other Asian countries. Although the global incidence of HIV has fallen slightly since 2010, there are still more than two million new infections each year.