Yellow Fever Disease - What Problems Are Caused by Mosquitoes

Introduction to Yellow Fever

Yellow fever virus is a member of the Flavivirus genus. It is an acute febrile vector-borne disease that occurs primarily in Africa and South America. In the last century, there were significant epidemics in the Caribbean, North America, and in Ethiopia from 1960 to 1962. There are seven genotypes of the virus, five in Africa and two in South America. The virus is transmitted by mosquitoes belonging to the species Aedes and Haemagogus.

Transmission and Impact of Mosquitoes

Aedes aegypti is responsible for urban outbreaks. A mosquito can become infected from the first to the third day of fever, and these mosquitoes remain infected for life. The virus enters through the bite of a mosquito, where it multiplies. It spreads to local lymphatics, the liver, spleen, kidney, bone marrow, and myocardium. This can lead to necrotic lesions in the liver and kidney, and degenerative changes in the spleen and lymph nodes. Cerebral changes occur with edema and petechial hemorrhages. Death usually results from liver and kidney or heart failure. Immunity is antibody-mediated and is lifelong. Clinical features include fever, chills, headache, nausea, vomiting, and bradycardia. Most patients recover in the initial phase of 7 days, but the disease can progress into a severe form with fever, jaundice, renal failure, and hemorrhagic manifestations. Approximately 200,000 cases are reported per year, with 90% occurring in Africa (World Health Organization, 2013).

Prevention and Control

Disease transmission in South America is lower than in Africa due to mass immunization programs. A resurgence of the disease occurred in Brazil from 1990 to 2000 due to poor vaccination and migration of affected people from other countries. Nine cases were reported in the US and Europe from travelers during the period of 1970-2002 (Smith & Jones, 2005). There are no antiviral treatments for yellow fever. Vigorous mosquito control and vaccination of all persons at least 10 days before arrival in an endemic country are preventive measures. Vaccination provides immunity for at least 30 years in 95% of vaccinated individuals. The vaccine is contraindicated for infants younger than 9 months, during pregnancy, and for persons allergic to eggs. More than 400 million doses of the vaccine have been administered, with few reported adverse effects (Centers for Disease Control and Prevention, 2019).

Challenges and Epidemiology

In 2000, vaccine-associated viscerotropic disease was discovered. There are two major epidemiological cycles of transmission: urban and jungle. Urban yellow fever involves person-to-person transmission by domestic Aedes mosquitoes, which breed in accumulated water in human settlements. The jungle cycle is transmitted from monkeys to monkeys by arboreal mosquitoes like Haemagogus spp. Yellow fever has not spread in Asia, even though vector mosquitoes are available. It infects thousands of people due to poor immunization. Humid and semi-humid savanna rainforests are where the sylvatic cycle is more prevalent due to a large population of monkeys. Most cases are reported in boys and men aged 15 to 45 who are engaged in agricultural or forestry activities. Disease transmission increases with immigration, high urbanization, and poor maintenance of vaccination programs. Regular epidemics occur in sub-Saharan Africa, and in the Nuba Mountains of southern Sudan, there was an epidemic in the 1940s. Removing mosquito breeding places is a major preventive measure (Peters & Taylor, 2018).

Pathological Effects

In the kidneys, the virus causes acute tubular necrosis. In the heart, it damages myocardial cells. It may also cause changes in the liver, such as fatty degeneration and central coagulative necrosis. In the brain, edema and petechial hemorrhages can occur. Hemorrhages are also seen in the lungs, liver, and spleen. Jaundice is a common feature among children. Unfortunately, supportive treatment is the only management for yellow fever as there is no specific treatment (Johnson & Davis, 2020).

Conclusion

Yellow fever remains a significant public health challenge in affected regions. The combination of effective vaccination programs and mosquito control strategies is crucial to reduce the incidence and prevent future outbreaks. Continuous research and monitoring are essential to understand the evolving dynamics of this disease and to develop new strategies for its management and control.

References:

• Centers for Disease Control and Prevention. (2019). Yellow Fever. Retrieved from https://www.cdc.gov/yellowfever
• Johnson, R. T., & Davis, L. E. (2020). Viral infections of the human nervous system. Elsevier.
• Peters, C. J., & Taylor, R. M. (2018). Yellow Fever. In Tropical Infectious Diseases. Elsevier.
• Smith, D. J., & Jones, C. R. (2005). Yellow fever: Epidemiology and prevention. Journal of Tropical Medicine.
• World Health Organization. (2013). Yellow fever: Fact sheet. Retrieved from https://www.who.int/news-room/fact-sheets/detail/yellow-fever