A disease is holoendemic when essentially every individual in a population is infected.[1][2]
Although the infection is ubiquitous, symptoms of disease do not appear equally across age groups. The young are more likely to express pathogenic responses, whilst the older hosts will carry the disease asymptomatically, or with reduced damage, due to adaptive immunity. Therefore, holoendemic diseases differ from hyperendemic[3] diseases, of which symptoms are expressed equally by members across all age groups of a population.[4][5]
Holoendemicity is frequently seen with malaria, specifically the strain caused by Plasmodium falciparum, in several regions of sub-Saharan Africa (one study found that 98.6% of the population had traces of the pathogen within a 4 month period[6]). While individuals of all ages risk exposure to malaria, those under the age of five are particularly susceptible to the disease. Children account for the majority of both local and global malaria cases[7] because they lack the adaptive immunity that comes with repeated exposure.[8] Other examples of holoendemic diseases include ocular trachoma in certain areas in sub-Saharan Africa, where virtually all children in those populations have been infected,[9] and hepatitis B in areas of the Marquesas Islands.[10]
^Stich, August; Oster, N.; Abdel-Aziz, I.Z.; Stieglbauer, G.; Coulibaly, B.; Wickert, H.; McLean, J.; Kouyaté, B.A.; et al. (2006). "Malaria in a holoendemic area of Burkina Faso: a cross-sectional study". Parasitology Research. 98 (6): 596–599. doi:10.1007/s00436-005-0104-9. PMID16416123. S2CID27192358. Note:"In the study area, like other holoendemic areas, youth is a risk factor for malaria. In comparison, adults in such areas have acquired permunition and can more readily resist infection and tolerate various symptoms associated with malaria."
^Trape, Jean-Francois; Rogier, Christophe; Konate, Lassana; Diagne, Nafissatou; Bouganali, Hilaire; Canque, Bruno; Legros, Fabrice; Badji, Assane; Ndiaye, Gora (1994-08-01). "The Dielmo Project: a Longitudinal Study of Natural Malaria Infection and the Mechanisms of Protective Immunity in a Community Living in a Holoendemic Area of Senegal". The American Journal of Tropical Medicine and Hygiene. 51 (2): 123–137. doi:10.4269/ajtmh.1994.51.123. ISSN0002-9637. PMID8074247. Notes: "The incidence of malaria attacks was 40 times higher in children 0--4 years of age than in adults more than 40 years old. Our findings suggest that sterile immunity and clinical protection are never fully achieved in humans continuously exposed since birth to intense transmission."
^Rogier, Christophe; Trape, Jean-Francois; Commenges, Daniel (1996-06-01). "Evidence for an Age-Dependent Pyrogenic Threshold of Plasmodium falciparum Parasitemia in Highly Endemic Populations". The American Journal of Tropical Medicine and Hygiene. 54 (6): 613–619. CiteSeerX10.1.1.887.5845. doi:10.4269/ajtmh.1996.54.613. ISSN0002-9637. PMID8686780. Note: "From then on, it decreased with age (P < 0.001), first rapidly in children, then slowly in adults, as is classically observed in areas of malaria holoendemicity."
^Lewallen, Susan; Courtright, Paul (2001). "Blindness in Africa: present situation and future needs". British Journal of Ophthalmology. 85 (8): 897–903. doi:10.1136/bjo.85.8.897. PMC1724094. PMID11466240. Notes: "Although the prevalence of active disease is similar for boys and girls, adult women tend to have more active disease than adult men, probably due to their more frequent interaction with children. In some areas trachoma is holoendemic—every child acquires active trachoma and every adult shows evidence of conjunctival scarring."
^Chanteau, S.; Sechan, Y.; Moulia-Pelat, J. P.; Luquiaud, P.; Spiegel, A.; Boutin, J. P.; Roux, J. F. (June 1993). "The blackfly Simulium buissoni and infection by hepatitis B virus on a holoendemic island of the Marquesas archipelago in French Polynesia". The American Journal of Tropical Medicine and Hygiene. 48 (6): 763–770. doi:10.4269/ajtmh.1993.48.763. ISSN0002-9637. PMID8333570.
