The word "host" refers to an animal that can be infected with a particular disease. The term "vector" refers to an organism which can carry a particular disease-causing agent (such as a virus or bacteria) without actually developing the disease. The vector can then pass the virus or bacteria on to anew host. Therefore any organism is capable of carrying the disease  but it is known that mostly the mosquito species is the organism that carries and transmits this deadly disease.

Previous studies with a limited number of strains have indicated that there are two genotypes of yellow fever (YF) virus in Africa, one in west Africa and the other in east and central Africa. Phylogenetic analysis using parsimony and neighbor-joining algorithms identified five distinct genotypes: central/east Africa, east Africa, Angola, west Africa I, and west Africa II.

Yellow Fever is in the the Flavivirus genus family which is generally transmitted to vertebrates by mosquitoes or ticks and frequently cause significant human morbidity and mortality. Known diseases in the family include dengue virus, Japanese encephalitis virus, tick-borne encephalitis virus, West Nile virus, and YF. Technically the links to every one of these disease can be traced back to Yellow fever and has likely changed form in symptoms but mosquitoes carry an immense amount of diseases so it wasn't a shock that Yellow fever has mutated to such modern day diseases seen.

The transmission cause of the disease is categorized into three different  types: sylvatic, intermediate, and urban. It was the first illness shown to be transmissible via filtered human serum (i.e. a virus), and transmitted by mosquitoes. The viruses infect, amongst others, monocytes, macrophages and dendritic cells. They attach to the cell surface via specific receptors and are taken up by an endosomal vesicle. Inside the endosome, the decreased pH induces the fusion of the endosomal membrane with the virus envelope. Thus, the capsid reaches the cytosol, decays and releases the genome.