Yellow Fever- The fear of a quick death

Abstract

Yellow fever caused by a small bite of a mosquito was a reason for many epidemics in the past around the world. It still remains a threat to travellers as well as people who live in the area of high risk.

Introduction

Yellow fever is caused by flavivirus and it’s transmitted by infected mosquito just like Malaria. Female infected mosquito will bite a human and injects its saliva that will realise the virus and enter the bloodstream. All people who are unvaccinated are at risk of being infected with the virus in the areas where the transmission is active, which is Africa and South America. There is no medication to treat yellow fever infection. It’s a threat to people travelling to those countries as well as to the people who live in those areas. Therefore a good strategy is needed to eliminate the yellow fever epidemic, control any outbreaks and protect people. Effective vaccination against yellow fever has been available for many years now and had a significant reduction in cases and number of deaths however is that enough to protect us from the virus?

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An infected person with yellow fever will mostly have symptoms just like during any normal fever; which includes headache, muscle pains, vomiting and loss of appetite.(WHO,2008a) However symptoms only last couple of days for those people. Some infected patients will get more toxic symptoms and body system parts like kidney and liver are affected. This toxic phase will also develop jaundice which is when skin and eyes turn yellow.(NHS,2018) It then gets worse and bleeding occurs from eyes, nose or mouth and patient dies within 10 days.(WHO,2008a) This is why Yellow Fever is described as a quick death. This is how Yellow fever is diagnosed through the presence of symptoms however there are some other testing which can detect the presence of a Virus.(A.Ayala,2008) One of is Polymerase chain reaction(PCR)test which can be used at the early stage and then in later stage the ELISA assay can be carried out to identify antibodies. Yellow fever can be transmitted either in urban area or sylvatic setting. Figure.1 shows a diagram to explain both areas of transmission. Sylvan Cycle includes transmission between both non-human primates as well as human. Inside the Urban Cycle the infected person can come from the sylvan cycle where for example the person works in the forest or from mosquitos found in the urban area. Much fever cases are reported in South America compared to Africa because transmission does occur from enzootic sources like from monkey to human through mosquito.(E.Ryan, 2018)

Figure 1. Shows Transmission Cycles of Yellow Fever.

The first recorded epidemics of yellow fever occurred in Mexico and Guadeloupe in 1648.( D.J. Rogers,2006)Through the 18th and 19th centuries the epidemics of yellow fever have occurred all over the world including Europe , Caribbean and United States. The biggest previous outbreak has started in 1986 in Nigeria where it infected 116,000 people and killed 24,000(D.Butler,2016) The most recent outbreak happened in Angola in 2015 which was reported to be the largest spread in Africa in more than 20 years with 884 cases. (F.Shearer,2018)

Most of the spread of the virus was due to migration of people. People who visit the countries with high risk of yellow fever may not be aware of the risk and then bring the disease to the country free from the virus. This is why many countries now require proof of vaccination against yellow fever before entering. (WHO,2008a) This prevents the spread of the disease across to other countries. However this is not always effective as in 2016 a few unvaccinated Chinese workers who travelled to the outbreak zone in Angola got infected with the virus. When returned to China there was a raised concern for yellow fever that it would gain uncontrollable foothold in Asia. (F.Shearer,2018)

The most important point is to prevent and control the yellow fever spread. To make sure that any outbreaks are rapidly contained to avoid any epidemics. The importance of The Eliminate of Yellow Fever Epidemics Strategy is to firstly protect those who are at risk. Secondly prevent the yellow fever from spreading internationally and lastly to contain the outbreaks as fast as possible. (WHO, 2016b). The aim of this strategy is to contain the countries that are most vulnerable to outbreaks of yellow fever. There are a few different measures in place by public health for a long term strategy to eliminate the outbreaks of yellow fever.

One of them is vaccination. In the 1930s a production of effective vaccine took control over the yellow fever.(D.Rogers,2006) Figure 2 Shows the number of cases of Yellow Fever in Africa since the vaccination been introduced and as the vaccination number increased each year the number of cases varied. It seems that the number of cases increased and decreased each year between 1939 and 1953.This could have been due to fast infection rate as mosquitos can increase in size very fast. As well as people weren’t vaccinated everywhere in Africa just in places were yellow fever cases were reported. However mass vaccination has been introduced because it is an effective and safe vaccine where only one dose provides immunity for lifetime. It’s affordable for anyone therefore this elimination strategy is a low-cost measurement. From 2017 the vaccine against yellow fever has been introduced in routine infant immunization programmes in 36 of the 42 countries of those at high risk for yellow fever in Africa and America (WHO,2018). This programme ensures that everyone is vaccinated and it’s harder for the virus to be spread however there are still 6 countries which are not included in the program and this could be a problem. Another strategy is very simple to make sure people are aware of the infection and protect themselves from the mosquito bite. Educating people on the disease and making them aware of the areas of high risk. One of the high cost measurements is vector surveillance which allows controlling the yellow fever mosquito species to measure the risk of outbreak. Knowing where these mosquitos are distributed will allow the country to prioritize the areas of high infections for laboratory testing for yellow fever. Building more laboratories for those testing is another high cost measurement.

Figure2. Shows Number of yellow fever cases between 1939-1953 in Africa.

These strategies do come with some issues like the control of mosquitos; it’s hard to find all the specific mosquitos that cause the yellow fever around the country especially when the climate changes so frequently meaning they will migrate from one place to another. There is also the limitation of effective insecticides that can be used against the adult vectors which is due to resistance. There are some people who are excluded from vaccination against yellow fever. These include children who are below the age of 9 months, pregnant women as well as people with allergies to egg protein and people with immunodeficiency. Therefore this is still a large amount of people who are not vaccinated and are prone to be infected with the virus.

Even with some of the limitations to those strategies it is very important to have them in place. Early detection can be accomplished by monitoring yellow fever surveillance. This then helps to monitor and control any outbreaks. This is very important to determine which areas are at high risk for Yellow fever to allow fast action to control the outbreaks. Testing will be carried out and emergency vaccination takes place as soon as possible if there is a sign of outbreak, this limits the spread of infection. It is sometimes very difficult for early detection of yellow fever because it’s hard to distinguish this disease from other ones with the similar symptoms for example malaria. (J.Vainio,1998)

Conclusion

It is very hard to eliminate yellow fever completely as numbers of mosquitos and their habitats increase each year.  However improved surveillance and increased number of vaccinations around the world means much greater control over the disease. This is why it’s important to monitor the disease and have strategies in place to make sure we have the control of the yellow fever and not the virus over us to prevent any future infections and subsequent deaths around the world.(1,322)

References

Image of Yellow Fever transmission paths Figure 1 .adapted from

M.Gershman,J.Staples(2012) ‘Yellow Fever’ ,’Netter’s Infectious Diseases’ Pages 383-389 [Online] Available at https://www.sciencedirect.com/science/article/pii/B9781437701265000641 (Accessed on 29.04.2019)

Figure 2 . Graph adapted from the original table from

 J.Vainio and F.Cutts(1998) London School of Hygiene and Tropical Medicine, ‘Yellow Fever’ [Online] Available at https://apps.who.int/iris/bitstream/handle/10665/64455/WHO_EPI_GEN_98.11.pdf (Accessed on 05.05.2019)

Two peer-reviewed articles with the numbers of citation.

Here I used Google Scholar

D.Rogers, A.Wilson , S.Hay , A.Graham(2006) ‘The Global Distribution of Yellow Fever and Dengue’ [Online] Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164798/ (Accessed on 08.05.2019)Cited by 180

F.Shearer, J.Longbottom,A.Brownie, D.Pigott, O.Brady,M.Kraemer et al (2018) ‘Existing and potential infection risk zones of yellow fever worldwide: a modelling analysis’ [Online] Available at https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(18)30024-X/fulltext (Accessed on 08.05.2019) Cited by 23

For this one I used Web of Science

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