Yellow fever.docx

**Yellow fever** **Learning objectives:** - Describe the clinical presentations including phases of yellow fever and potential complications. - Explain the cycle of infection of yellow fever including the role of mosquito vectors - Determine geographic distribution of yellow fever...

**Yellow fever** **Learning objectives:** - Describe the clinical presentations including phases of yellow fever and potential complications. - Explain the cycle of infection of yellow fever including the role of mosquito vectors - Determine geographic distribution of yellow fever and highlighting endemic regions - Identify preventive and control strategies directed toward yellow fever. **Overview:** Yellow fever was historically the first described viral hemorrhagic fever (VHF) and its causative agent, the yellow fever virus (YFV), is the prototypic member of the family Flaviviridae. Yellow fever is an epidemic-prone mosquito-borne vaccine preventable disease that is transmitted to humans by the bites of infected mosquitoes. Yellow fever is caused by an arbovirus. **Clinical presentation:** **Yellow fever is described as a biphasic disease:7** **Viremic phase:** - High fever, with a mean duration of three days, myalgia, headache, lack of appetite and nausea. - Mostly, these symptoms subside within 2 to 4 days. **Toxemic phase:** - Takes place in approximately 15% of patients and begins after a period of clinical improvement that follows the first phase, lasting 24 hours on average. - It is characterized by recrudescence of high fever, chills, worsening of headache and myalgia, and involvement of various organs and systems. - It is in this second phase that, later, icteric discoloration of the skin that characterizes the disease develops. - There may be bleeding, kidney dysfunction with oliguria, as well as cardiovascular dysfunction and neurological impairment with seizures. - Often, the unusual pairing of fever with bradycardia (Faget sign) is observed. - Up to half of these patients progress to death in 10 to 14 days, and the rest recover without significant sequelae **Descriptive epidemiology** **Person:** No one is immune from yellow fever, and it occurs in people of all ages and races. The highest mortality rates are reported in infants and the elderly, who often have depressed immune systems. **Place:** Yellow fever occurs in sub-Saharan Africa and tropical South America, where it is endemic and intermittently epidemic. In areas of Africa with persistent circulation of yellow fever virus, natural immunity accumulates with age; consequently, infants and children are at greatest risk for disease. In South America, yellow fever occurs most frequently in unimmunized young people exposed to mosquito vectors through their work in forested areas. **Time:** **Cycle of infection:** **Infectious agent:** Yellow fever (YF) virus is a single-stranded RNA virus that belongs to the genus Flavivirus. **Reservoir:** Urban area: humans and Aedes mosquitoes Forest area: monkeys, non-human primates, and forest mosquitoes **Exit:** The exit is the skin through mosquito bite. **Source of infection:** In humans, new infections can emerge when virus-containing saliva is injected into a non-immune host during the bite of female Aedes aegypti mosquitoes (In Urban type) or that of Aedes Africans and Aedes Sympsoni mosquitoes (In jungle type) **Mode of Transmission:** Vector borne transmission: Bites by infected mosquitoes are the only mode of transmission. Mosquitoes acquire the virus when they feed on a viremic host, after which the virus infects many tissues, including the salivary glands. The mosquitoes are infected for life. The 'extrinsic incubation period', the time required for the mosquito to become infective, is about ten days, depending on the temperature. **Yellow fever is not transmitted from person-to-person.** **Inlet:** The inlet is the skin through mosquito bite. **Susceptibility:** Susceptibility is general. **Incubation period:** The incubation period for yellow fever is 3 to 6 days and may reach 10-15 days. **Period of communicability:** The blood of patients is infective for mosquitoes from shortly before onset of fever until 3 - 5 days of illness. The incubation period in Aedes aegypti mosquitoes is commonly 9 - 12 days at the usual tropical temperatures. Once infected, mosquitoes remain so for life. **Prevention:** **1. Vaccination** Vaccination is the most important means of preventing yellow fever. The yellow fever vaccine is safe, affordable and a single dose provides life-long protection against yellow fever disease. A booster dose of yellow fever vaccine is not needed. The vaccine provides effective immunity within 10 days for 80--100% of people vaccinated, and within 30 days for more than 99% of people vaccinated. People who are usually excluded from vaccination include: - Infants aged less than 9 months. - Pregnant women -- except during a yellow fever outbreak when the risk of infection is high. - People with severe allergies to egg protein. - People with severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or who have a thymus disorder. A valid international certificate of immunization against yellow fever is required by many countries for entry of travelers coming from or going to recognized yellow fever zones of Africa and South America. The certificate is valid 10 days after the date of immunization. The quarantine measures are applicable for up to 6 days **2. Vector control** The risk of yellow fever transmission in urban areas can be reduced by: - Eliminating potential mosquito breeding sites, including by applying larvicides to water storage containers and other places where standing water collects. - Preventive measures, such as wearing clothing to minimize skin exposure and repellents are recommended to avoid mosquito bites. - The use of insecticide-treated bed nets is limited by the fact that Aedes mosquitos bite during the daytime. - Both vector surveillance and control are components of the prevention and control of vector-borne diseases, especially for transmission control in epidemic situations. For yellow fever, vector surveillance targeting Aedes aegypti and other Aedes species will help inform where there is a risk of an urban outbreak. **3. Epidemic preparedness and response** Prompt detection of yellow fever and rapid response through emergency vaccination campaigns are essential for controlling outbreaks. However, underreporting is a concern; WHO estimates the true number of cases to be 10 to 250 times what is now being reported. WHO recommends that every at-risk country has at least one national laboratory where basic yellow fever blood tests can be performed. A confirmed case of yellow fever in an unvaccinated population is considered an outbreak. A confirmed case in any context must be fully investigated. Investigation teams must assess and respond to the outbreak with both emergency measures and longer-term immunization plans **Control measures:** **1.Surveillance and reporting** It should be noted that it is one of the acute hemorrhagic fevers' syndromes with a risk of importation through travelers Case report universally required under international health regulations (IHR) Immediate mandatory case-based reporting. **Case definition** **Suspected case:** An illness characterized by acute onset and constitutional symptoms followed by a brief remission and a recurrence of fever, hepatitis, and albuminuria. In some cases, leading to renal failure, shock and generalized hemorrhages Epidemiological evidence (history of travel to endemic countries within 1 week) **Confirmed case:** Suspect case, which is laboratory confirmed, i.e. a 4-fold or greater rise in yellow fever antibody titer with no history of recent yellow fever immunization and no evidence of cross-reactions to other flaviviruses. **2.Isolation:** During the first few days of illness, protect infected people from further mosquito exposure by keeping them indoors or under a mosquito net, so they do not contribute to the transmission cycle. **3. Case management** No specific treatment for yellow fever. Symptomatic and supportive care is critical. Most cases are asymptomatic; however, case fatality of severe cases can be 20-50%. Management consists of vasoactive medications, fluid resuscitation, ventilator management, and treatment of disseminated intravascular coagulopathy (DIC), haemorrhage, secondary infections, and renal and hepatic dysfunction. **4.Tracing the contacts of the patients** **5.Environmental reassessment for potential for transmission and vector control measures.** **References:** World Health Organization. Yellow fever \[online\]. 2023 May 31 \[cited 2024 Aug 30\]. Available from: Litvoc MN, Novaes CT, Lopes M. Yellow fever. Revista da Associação Médica Brasileira. 2018;64, 106-13.‏ Monath TP, Vasconcelos PF. Yellow fever. J Clin Virol. 2015 Mar; 64:160-73. European Centre for Disease Prevention and Control. Facts about yellow fever \[online\]. 2021 May 31 \[ cited 2024 Aug 30\]. Available from:. Simon LV, Hashmi MF, Torp KD. Yellow Fever. StatPearls \[Internet\]. Treasure Island (FL): StatPearls Publishing; 2024 Jan. Available from:. Centers for Diseases Control and Prevention. Yellow fever \[ online\]. 2023 May 1 \[ cited \[ 2024 Aug 30\]. Available from:. LOWA Health and Human services. Yellow fever \[Online\]. \[ cited 2024 Aug 30\]. Available from:. **Viral Hemorrhagic fever** **Learning objectives:** - Define Viral hemorrhagic fever. - Identify population at risk. - Describe geographic distribution of the disease. - Illustrate implicated infectious agents, reservoir as well as mode of the transmission of viral hemorrhagic fever. - Demonstrate preventive and control measures. **Overview:** Viral hemorrhagic fevers include a spectrum of relatively mild to severe life-threatening diseases characterized by sudden onset of muscle and joint pain, fever, bleeding, and shock from loss of blood. In severe cases, one of the most prominent symptoms is bleeding, or hemorrhaging, from orifices and internal organs. In the Eastern Mediterranean Region, the main viral hemorrhagic fevers are yellow fever, Rift Valley fever, dengue fever, Crimean--Congo hemorrhagic fever and Ebola virus disease. **Descriptive epidemiology:** **Person:** People in these areas who are most at risk are those who do animal research, healthcare workers and people caring for patients where outbreaks are occurring. **Place:** The emergence and re-emergence of viral hemorrhagic fevers is a growing concern worldwide. In the past 2 decades, the Eastern Mediterranean Region has witnessed major outbreaks as well as sporadic cases of yellow fever, Rift valley fever, severe dengue and Crimean-Congo hemorrhagic fever. The viruses depend on their animal hosts for survival. They are usually restricted to the geographical area inhabited by those animals, or a specific arthropod vector. The viruses are endemic in areas of Africa, South America and Asia. **Cycle of infection:** **Infectious agent:** These illnesses are caused by viruses from 4 groups: - Arenaviruses ((Lassa, Junin, Machupo, Guanarito, and Sabia). - Filoviruses (Ebola and Marburg viruses). - Bunyaviruses ((Crimean-Congo hemorrhagic fever \[CCHF\] and Rift Valley fever \[RVF\]). - Flaviviruses. **Reservoir** Many wild and domestic animals, ticks, and mosquitoes are known to carry some of the VHF agents, although reservoirs have not been identified for all VHF agents. Rodents are known to be the carriers of Lassa, Crimean Congo hemorrhagic, and Rift Valley fever viruses. Mosquitoes, ticks, and animals (including rodents, foxes, hares, and ground feeding birds) are known to carry bunyaviruses that cause VHFs. **Mode of transmission:** **here are multiple modes of transmission for viral hemorrhagic fever:** - Person to person through direct contact with symptomatic patients, body fluids, or cadavers - Inadequate infection control in a hospital setting (Crimean--Congo hemorrhagic fever, Lassa, Ebola) - Slaughtering practices - Consumption of raw meat from infected animals or unpasteurized milk (Crimean--Congo hemorrhagic fever, rift valley fever) - Direct contact with rodents, or inhalation of or contact with materials contaminated with rodent excreta (Lassa) - Mosquito bites (rift valley fever, dengue) or ticks (Crimean--Congo hemorrhagic fever). **Incubation Period:** The incubation periods for VHFs range from 1--21 days, with an average of 3--10 days. **Period of communicability:** Infected individuals are generally considered to be infectious for a variable period preceding the onset of symptoms (up to about three weeks for some VHFs) and during clinical symptoms. The virus may remain in the blood and in secretions for months after an individual recovers. Contaminated bedding and medical equipment may remain infectious for several days. For some VHFs, the virus may remain viable for a variable duration post-mortem, permitting transmission from recently deceased patients. **Prevention:** No vaccines are available to prevent most of these diseases. But there are vaccines for yellow fever, Ebola, and Argentine hemorrhagic fever Because many of the hosts that carry hemorrhagic fever viruses are rodents, disease prevention efforts in endemic areas include controlling rodent populations and keeping rodents away from homes and workplaces. **For viruses spread by ticks or mosquitoes, prevention focuses on:** Controlling mosquitoes and ticks in your environment Using insect repellent, correct clothing, bed nets, window screens, and other insect barriers to prevent being bitten. **Control:** **Surveillance and Reporting:** Identify cases as early as possible to prevent transmission to other persons or animals. **Isolation and Quarantine Requirements**: Minimum Period of Isolation of Patient Place on hemorrhagic fever-specific barrier precautions with airborne infection isolation, contact, and droplet precautions, and with double gloving and strict hand hygiene, impermeable gowns, face shields, eye protection, and leg and shoe coverings, until clinical illness has resolved **Protection of Contacts of a Case** There is no immunization or prophylaxis for contacts of cases. Health care workers and other contacts of known or suspect cases of VHF should practice recommended VHF precautions to reduce their chances of acquiring VHF. Individuals who have had any contact with infectious patients should be monitored by their health care provider for the maximum incubation period for the specific agent. **References:** Centers For Diseases Control and Prevention. About Viral Hemorrhagic Fevers \[online\]. 2024 Apr 15 \[ cited 2024 Aug 30\]. Available from:. World Health Organization. Hemorrhagic fevers, Viral \[online\]. \[2024 Aug 30\]. Available from:. GOV.UK. Guidance Viral hemorrhagic fevers: origins, reservoirs, transmission and guidelines \[online\]. 2018 oct 12 \[ cited 2024 Aug 30\]. Available from:. Massachusetts Department of Public Health, Bureau of Communicable Disease Control. Viral Hemorrhagic Fevers. 2006: 904-06. Mangat R, Louie T. Viral Hemorrhagic Fevers. Treasure Island (FL): StatPearls Publishing; 2024 Jan. Available from:.