Yellow Fever In Bolivia: Endemic Or Not?

Yellow fever is a disease spread by the bite of an infected mosquito. It is endemic in several Latin American countries, including Bolivia. The mosquito that carries the disease, Aedes aegypti, has historically been controlled through vaccination campaigns. However, the mosquito has re-infested many areas, spreading other diseases like dengue, zika, and chikungunya, and increasing the risk of yellow fever epidemics. Travellers to Bolivia are advised to take precautions against mosquito bites and to get vaccinated.

Yellow fever is endemic in Bolivia

Yellow fever is a serious and sometimes fatal disease. The risk of contracting yellow fever is highest in the northern Beni and Pando regions of Bolivia, especially in the localities of Guayaramerin and Riberalta. In other parts of the country, such as eastern and western Beni and Nor Cinti province in the south, the risk is lower but may still be a concern for certain high-risk groups.

To prevent yellow fever, a vaccine is usually recommended for all those who travel into risk areas. In Bolivia, a yellow fever vaccination certificate is required for travellers aged 1 year or older arriving from countries with a risk of yellow fever transmission. The vaccination requirement is in place to protect against the disease, as the Aedes aegypti mosquito is present in the country. The vaccine is typically included in routine immunization schedules for children between 9 and 18 months of age in endemic countries. However, a drop in vaccination coverage can result in a high risk of new outbreaks.

In addition to vaccination, there are other measures that can be taken to reduce the risk of yellow fever transmission. These include avoiding mosquito bites, especially during the daytime when the Aedes aegypti mosquito is most active, and taking precautions such as wearing long sleeves and long trousers, using insect repellents, and sleeping under a mosquito net.

Aedes aegypti mosquitoes spread the disease

Aedes aegypti mosquitoes, also known as yellow fever mosquitoes, are vectors for transmitting numerous pathogens, including the yellow fever virus. The mosquitoes originated in Africa and are now found in tropical, subtropical, and temperate regions worldwide. They are particularly prevalent in densely populated areas with unreliable water supplies, waste management, and sanitation issues.

The Aedes aegypti mosquito is relatively small, ranging from 4 to 7 millimeters in length, and can be recognized by its black and white markings. The females are larger than the males and are the only ones that bite, as they require blood to mature their eggs. These mosquitoes are attracted to chemical compounds emitted by mammals, including ammonia, carbon dioxide, lactic acid, and octenol, which help them find a host.

The Aedes aegypti mosquito lays its eggs in water, specifically on the inner walls of containers above the waterline. The eggs can survive drying out for up to 8 months and will turn black soon after being laid. The larvae feed on bacteria and develop over a few weeks until they reach the pupa stage. The pupae then develop into adult, flying mosquitoes.

The lifespan of an adult Aedes aegypti mosquito is about two to four weeks, but the eggs can remain viable for over a year in a dry state, allowing the mosquito to re-emerge after cold winters or dry spells. This ability to survive in dry conditions contributes to the spread of the disease, as the mosquitoes can re-establish themselves in previously infested areas.

To prevent the spread of yellow fever and other Aedes-borne diseases, population control efforts and genetic modification of the mosquitoes have been implemented. Pyrethroids are commonly used to control Aedes aegypti populations, but this has led to the development of insecticide resistance in some cases. Genetic modification approaches, such as the OX513A mosquitoes developed by Oxitec, have shown success in reducing target mosquito populations by more than 90%.

Bolivia requires a yellow fever vaccination certificate for travellers

Yellow fever is endemic in Bolivia, and the country requires travellers arriving from regions with the virus to provide a valid yellow fever vaccination certificate. The vaccine is recommended for all travellers over nine months old who plan to travel east of the Andes at altitudes under 7,500 feet (2,300 metres). Regions above 7,500 feet do not have the virus, and the vaccine is not recommended for areas with higher altitudes.

The Pan American Health Organization (PAHO) states that yellow fever is endemic in several Latin American countries, including Bolivia. Since the 1950s, urban epidemics have been controlled through campaigns to eradicate the Aedes aegypti mosquito. However, decades later, the mosquito re-infested most areas, spreading other Aedes-borne diseases like dengue, zika, and chikungunya, and re-establishing the risk of urban fever epidemics.

To prevent yellow fever, enzootic countries introduced the yellow fever vaccine into routine immunization schedules for children between 9 and 18 months of age. However, a drop in vaccination coverage has resulted in a high risk of new outbreaks. The Centers for Disease Control and Prevention (CDC) recommends that all eligible travellers be up to date with their vaccinations, including COVID-19, before visiting Bolivia.

In addition to the yellow fever vaccination, the CDC and the World Health Organization (WHO) recommend the following vaccinations for travellers to Bolivia: typhoid, hepatitis A, polio, chikungunya, rabies, hepatitis B, influenza, COVID-19, pneumonia, meningitis, chickenpox, shingles, Tdap (tetanus, diphtheria, and pertussis), and measles, mumps, and rubella (MMR).

To stay healthy in Bolivia, travellers should also take precautions to avoid insect bites, practise food and water safety, and be aware of the risk of altitude sickness.

The vaccine is administered to children between 9 and 18 months old

Yellow fever is endemic in several Latin American countries, including Bolivia. The disease is spread by the Aedes aegypti mosquito, which has facilitated the spread of other diseases such as dengue, zika, and chikungunya. The Pan American Health Organization has created country profiles for yellow fever, including Bolivia, to assist decision-makers in prioritizing preventive actions against the disease.

Yellow fever can be prevented by administering a vaccine, and enzootic countries have introduced this vaccine into routine immunization schedules for children between 9 and 18 months old. However, the drop in vaccination coverage has resulted in a high risk of new outbreaks. A single dose of the yellow fever vaccine is routinely given to infants around 9-12 months old under the Expanded Programme on Immunization, but the long-term outcome of this vaccination in this age group is unknown.

The decision to vaccinate a child should be carefully evaluated, especially when it comes to travel-related vaccines. The Centers for Disease Control and Prevention (CDC) provides recommendations and requirements for vaccinations before international travel, including proof of yellow fever vaccination for entry into certain countries. While the yellow fever vaccine is considered safe and effective, it is essential to weigh the potential risks and benefits for each individual child.

In a clinical trial of the stabilized yellow fever vaccine from the Institute Pasteur, 77 children aged seven to eight months were observed. The most significant immediate and delayed side effect was fever, which occurred in 15.6% of children within 48 hours of vaccination and 12.9% within ten days. Other side effects included pain at the injection site (5.2%) and vomiting (1.3%). The seroconversion rate was 60%, lower than in adults and older children, but the vaccine was deemed safe and fairly effective for infants.

The risk of urban fever epidemics remains

Yellow fever is endemic in Bolivia. The disease has been a serious public health problem in the country since at least the 19th century, with urban epidemics controlled since the 1950s through the eradication of the Aedes aegypti mosquito. However, the mosquito has since re-infested most of the areas it previously occupied, spreading other Aedes-borne diseases like dengue, zika, and chikungunya, and re-establishing the risk of urban fever epidemics.

The risk of urban yellow fever epidemics in Bolivia is heightened by the significant spread of the Aedes aegypti mosquito across its cities. This mosquito species is a known vector of yellow fever, capable of transmitting the disease to human populations and causing severe outbreaks in urban areas. The presence of this mosquito, combined with the country's history of yellow fever outbreaks, underscores the ongoing threat of urban yellow fever epidemics.

The risk is further exacerbated by the decline in vaccination coverage, which has resulted in a high risk of new outbreaks. While enzootic countries have introduced the yellow fever vaccine into routine immunization schedules for children between 9 and 18 months of age, the overall drop in vaccination coverage increases the likelihood of outbreaks with varying magnitudes. Insufficient vaccination coverage can lead to lower herd immunity, making it challenging to prevent the spread of the disease within communities.

To address this ongoing risk, decision-makers must prioritize preventive actions and interventions. The Pan American Health Organization provides country profiles that offer a comprehensive analysis of the situation in endemic countries, including ecological and climatic factors, vector distribution, and key arboviral activity. By utilizing these resources and implementing targeted prevention and control measures, there is a higher chance of mitigating the risk of urban yellow fever epidemics in Bolivia.

Additionally, sustained epidemiological surveillance is crucial to monitor the presence and spread of the disease. With the Aedes aegypti mosquito now established in Bolivian cities, the possibility of a resurgence in urban yellow fever transmission remains a concern. By closely monitoring the situation and responding promptly to any reported cases, health authorities can better manage and contain potential outbreaks, protecting the population from the devastating consequences of urban yellow fever epidemics.

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