The immune system soon recovers somewhat, however, and keeps HIV levels fairly steady for several years. Eventually, though, the virus gains the upper hand.
The West African outbreak of Ebola has claimed more than 4, lives and this number is sure to rise. There is understandably a lot of fear about Ebola, but how does it actually compare with other fast-spreading infectious diseases?
Bubonic plague Plagues have been reported since biblical times, but it is difficult to know how serious these early epidemics were, or even what the infectious agent was. We now know that plague is a serious disease caused by the bacteria Yersinia pestis.
The Black Death is thought to have been bubonic plaguenamed after the presence of infected lymph nodes; it killed one-third of the population of Europe in the 14th century.
Bubonic plague killed one-quarter of the population of London inand the Great Plague of London killeda century later. Plague is spread by fleas that usually infest rodents. The disease is still found in parts of Asia, Africa and the Americas. Few humans are now infected, although outbreaks occasionally occur.
The extensive wildlife reservoir means that it will never go away. Influenza The war resulted in between 15 and 18 million deaths, but the flu pandemic killed more than twice that number. Influenza spreads rapidly by coughs and sneezes which release small droplets. These droplets may infect others while airborne or by contaminating surfaces.
Symptoms of the flu can start within a day or two of being infected and last for about a week. But virus shedding begins before the symptoms and one-third of cases show no symptoms at all.
The virus also readily mutatesso past infection does not necessarily provide future protection. The fatality ratio of seasonal influenza is low, usually claiming one in 1, lives, so it is often regarded as inconsequential. But a virus shift can cause a pandemic and increased rates of death.
Bird flu Of greater concern is the avian influenza reservoir in parts of Asia. If these viruses were to mutate and become easily transmitted between humans, public health services would be severely challenged by the resulting pandemic.
The basic reproduction number of an infection, usually expressed as R0, is defined as the expected number of cases that would arise from a typical primary case in a susceptible population.
If R0 is bigger than one, then the number of cases will increase until limited by control measures, behaviour change or the exhaustion of the supply of susceptibles.
If R0 is less than one, then the incidence of infection will decrease and the outbreak will fizzle.
Its infectious agent is a coronavirus, from a family often implicated in the common cold. Its mode of transmission was similar to that of influenza but its basic reproduction number, at over three, was twice that of the flu. The long four to five-day incubation period made it amenable to contact tracing, enabling the isolation of contacts before they became infectious.
It was largely these non-clinical interventions that succeeded in reducing the contact rate, and therefore the reproduction number, below one. The pandemic was brought to a halt and the infection eliminated, with the loss of lives.
However, another coronavirus is now responsible for cases of Middle East respiratory syndrome MERS and deaths. Ebola Ebola is not an airborne infection; it is spread by bodily fluids, which means that more intimate contact is required for transmission.
The basic reproduction number is usually estimated to be around two, although a recent estimate for hospital settings in Africa puts the value of R0 over four. It seems that transmission only occurs while the patient is symptomatic, so contact rates must be low even though the probability of transmission given contact is high.
The eight to ten-day average incubation period also suggests that contact tracing and isolation should be successful in halting the spread of infection. HIV was transmitted to humans in the s from a chimpanzee, but remained largely confined to what is now the Democratic Republic of Congo until undergoing an epidemiological transition in the s.
The resulting global HIV pandemic has infected nearly 75 million people. While transmission of HIV and Ebola both rely on the transfer of bodily fluids, there are major differences.
A HIV patient can be infectious for many years while not exhibiting any symptoms, and may be unaware of their status.Transcriptomic and Innate Immune Responses to Yersinia pestis in the Lymph Node during Bubonic Plague Bubonic plague is a zoonotic disease transmitted by fleas.
Two plasmids unique to Y.
pestis, many similarities were evident in the host response to infection with either WT or pYV. Students are unaware of the similarities that exist between the Bubonic Plague and AIDS.
Most high school textbooks do not mention the relationship and they talk about the HIV virus briefly in the chapter. Exploring the similarities and differences between the Black Death and HIV/AIDS, students write persuasive essays answering which is the "worse plague." Students discover the behaviors associated with getting acquired immune deficiency syndrome (AIDS) and study the infectious cycle for the human immunodeficiency virus (HIV) by playing a.
Human immunodeficiency virus infection and acquired immune deficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV).
Following initial infection, a person may not notice any symptoms or may experience a . This disease syndrome, termed at the time gay-related immunodeficiency disease (GRID), quickly became known as Acquired Immune Deficiency Syndrome, or AIDS. This handful of cases, noticed by a few highly observant clinicians, has ballooned into a worldwide pandemic; more than 36 million people are infected worldwide.
Bubonic plague: infected lymph nodes. It is vector-transmitted by fleas of rats particularly black rats (Rattus rattus) but also other rodents.
• Pneumonic plague: infected lungs (death rate 90%). Transmission by fleas and by aerosol from coughing (person to person). • Septicemic plague: infection of bloods.