Yellow Fever Disease Essay

Introduction

Yellow fever is a viral hemorrhagic disease (Flavivirus), which is transmitted through the bite of an infected Aedes aegypti mosquito, which is commonly found in the tropics. Jaundice characterizes the disease, hence the name 'yellow'. The disease primarily affects only humans and other primates. Yellow fever virus is an arthropod-borne single stranded RNA of the genus Flavivirus and family Flaviviridae.

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Individual characteristics

Individual characteristics of the organism causing yellow fever; the flavivirus is long, spherical, and with an enveloped caspid which is about 50 nm in diameter. The proteins on the surface of the caspid are aligned in an icosahedral symmetry. In addition, virus encoded proteins are present in mature virions. Virion RNA is the infectious stage. Virus particles have spiky surface projections. The nucleic acid is the infectious portion and is capable of transmitting the disease alone. Besides, the genome has one positive sense strand that is translated directly into protein and a single stranded RNA molecule. The female mosquitoes are primary vectors of the disease; the aedes mosquitoes normally strike during the day, the mosquitoes are increasingly resistant to insecticides.

Disease Process

A typical infectious disease includes the following components: agents, reservoirs, portals of entry and exit, modes of transmission and immunity.

Etiological agent: the causative agent of yellow fever is Flavivirus, a group of Arbo B-virus of the Togavirus family. Under natural conditions, the virus is a pantropic resulting from the continued culture in tissues. The virus multiplies in mosquito species without harming them ultimately transmitting the infection to humans.

Reservoirs: mosquitoes are the actual disease reservoirs since they ensure the regular transmission and pass on the virus via its progeny. In urban areas, the reservoirs are humans and mosquitoes while in the forests, monkeys, and mosquitoes of the forest species act as reservoirs.

Pathophysiology: the virus is transferred from the salivary glands of the mosquito via the bite during a blood meal. Replication takes place in the human host local tissues and the lymph nodes is capable of infecting a feeding mosquito at about 3 to 4 days and no human-to-human transmission of the disease is known.

Once the virus penetrates the human bloodstream, the hematogenous spreads to the bone marrow, kidney, spleen, and myocardium and lastly to the liver where further replication takes place. The secondary infection causes symptoms such as cerebral edema and cerebral hemorrhage. Disseminated intravascular coagulation involves reduced coagulation actor synthesis, altered platelet functioning and gastrointestinal mucosa bleeding.

Myocardial fiber injury results from direct viral activity and causes cloudy swelling and fatty changes that can ultimately cause death and shock. Other infection consequences include hemorrhage as well as secondary effects of active cytokines.

The mosquitoes are diurnal feeders and only females transmit the disease. The virus can only be transmitted from humans during 3to 4 days after initial onset of symptoms. Interruption of a female mosquito while feeding may result in it seeking another host, causing multiple transmissions during the feeding cycle. The incubation period of the mosquito is 12 to 21 days.

The virus enters the ovum of the female mosquito and can survive there awaiting moist seasons. Uninfected females provide viral amplification by biting on infected hosts. Approximately 3-10 virions are necessary for an infection to occur.

Symptoms; Most people suffering from yellow fever are asymptomatic but when symptoms occur they include fever, muscle pains, nausea and vomiting, mild headaches and backaches. Symptoms disappear four days after the infection. However, some patients might enter a toxic phase, 24 hours after recovery from initial symptoms, characterized by jaundice, dark urine, abdominal pains, and unusual bleeding.

Transmission patterns: there are three cycles of disease transmission. The first cycle is sylvatic/jungle. The cycle is confined to tropical rain forests where hosts are human working in the forests. The mosquito transmits the virus via the bite during blood meal to non-primate hosts or incidentally to human hosts, transmitting it to another mosquito.

The second transmission cycle is the intermediate/savannah cycle. The cycle is confined to moist savannahs and is the common outbreak cycle in Africa. Semi-domestic mosquitoes (those breeding in both domestic and wild areas) are the primary vectors which infect both monkeys and people, transmitting the virus to other mosquitoes. Many people acquire the virus simultaneously and the cycle acts as a bridge between jungle and urban area cycles causing an urban area epidemic.

The last transmission cycle is the urban cycle that occurs in urban areas. Large outbreaks of the disease occur when infected patients in areas introduce the virus with high mosquito density, or in areas where people have little immunity due to lack of vaccination.

Treatments available and their modes of action

No treatment has been developed against the prototype yellow fever virus. Vaccination is the countermeasure available for those inhabiting mosquito prone areas or those visiting yellow fever endemic areas. The vaccine protects against all yellow fever virus strains, and elicits a protective antibody response within ten days in most individuals.

There has been an attempt to develop anti-viral therapies that either directly targets yellow fever virus works indirectly by blocking detrimental host responses to infection.

Short term and long term prognosis of treatments

Approximately 85% of infected individuals fully recover from first illness stages without further disease progression and can acquire lifelong immunity from the disease. About half of 15% of patients who suffer from disease progression fully recover and acquire lasting immunity. The remaining half dies within 14 days from onset of symptoms.

Long-term effects are not common and delay in disease diagnosis occurs when patients are asymptomatic. Such delays heighten the risk of severe complications or even death, resulting from unrecognized synchronized diseases for example malaria.

Possible adverse effects of treatments

Common side effects of yellow fever vaccine include injection site reactions such as swelling and tenderness, joint pains, fever, headaches, flu-like symptoms and general body weakness. Other adverse effects include prickly feeling around the fingers, neck stiffness, extreme sensitivity to light, problems with speech and swallowing, severe lower back pains, loss of bowel control and behavioral changes including seizures and convulsions. Further, allergic reactions such as chest tightness, wheezing and breathing difficulties are associated side effects of yellow fever vaccines. In addition, little urination, unusual breeding, and jaundice are common side effects of YF vaccine. Serious side effects are more likely to occur in older adults.

In my case, I would opt for yellow fever vaccine as a prevention method. This is because the vaccine provides highly effective and durable immunity to residents of endemic areas as well as people travelling to mosquito prone residences. Besides, neurotrophic and viscerotropic adverse effects resulting from yellow fever vaccines are rare. The vaccine is safe despite its side effects, and it is recommended for pregnant women who suffer a potential exposure to the disease. Vaccination reduces the burdens of infectious disease, and mass vaccination campaigns are highly effective in vector eradication.

Yellow fever vaccination has many societal benefits since it reduces social concerns such as premature death and loss of household income. In addition, vaccination reduces the risk of an infected person to progress to disease severity. Another reason as to why I would choose vaccination is because it produces herd immunity that protects young infants and the elderly who cannot receive the vaccines. Community vaccination ensures fewer lives are lost from the disease and less income lost. Lastly, vaccination extends life expectancy and safeguards pregnant women from complications that would occur in the course of pregnancy.