By Muhammad Bilal
Edited by Emily DeMichele
As researchers delve deeper into the fascinating world of louse evolution (louse: plural:lice are small, wingless, parasitic insect that typically infests the hairs of animals, including humans), they continue to uncover secrets that shed light on the history of humanity itself. Recently, a biologist, who was visiting archaeological sites to study louse evolution, discovered lice nits (eggs) from the 1500-2000 years old mummies, which can be helpful to study ancient humans and their migration patterns (1). The parasitic lice diverged about 100-150 million years ago from bark lice and spread to infest different species of mammals around 65 million years ago (2). Lice are one of the oldest human ectoparasites (3). The history of human lice is about 3-4 million years old when the human crab lice evolved from the pubic lice of gorillas. The divergence between humans and gorillas occurred about 7 million years ago (4). The emergence of human body louse corresponds to when humans first started wearing clothes about 72000 ± 42000 years ago (5). Lice infestation is called pediculosis, and it is a global public health problem with a 19% prevalence of head lice in school children and 2% prevalence of crab or pubic lice in adults worldwide (6).
Your hair might be more than just a fashion statement or a way to express your personality. It could also be home to these tiny passengers, who might be carrying some unwelcome guests – pathogens. First, what are lice? They are small, wingless insects, possessing an elongated abdomen that is used to store blood or other ingested food. They have six pairs of legs ending with a claw with which they grasp hairs. There are 5,000 known species of lice, infesting a wide range of host species from birds to mammals. Their lifecycle starts when an adult female lays the egg which attaches to the base of hairs. It passes through three nymphal stages and 3rd nymph molts to an adult. The lice lifecycle is completed within 3-4 weeks and adult lives for up to 35 days. Based on their feeding habits, lice are divided into two main types: Biting and Sucking lice (7). Biting lice ingest skin scalp and skin products while sucking lice live on the host blood (8). In humans, three types of sucking lice are found throughout the world, body lice, head lice, and crab or pubic lice. The human body louse is the only louse that is known to transmit pathogens naturally (5).
Interesting Fact: The highest number of human body lice that has been recorded on one person is 30,000.
The human body louse is the vector of three diseases, Typhus fever Louse-borne relapsing fever, trench fever, and may have even played a major role in the bubonic plague (9).
Typhus fever, lice and human tragedy: An enemy of soldiers
The origin of typhus fever is unknown (13) but there are some documented proofs of typhus outbreak from 1083 (14). The disease has a long and tragic history, causing millions of deaths throughout human history. In 1546, a Florentine physician described typhus. Some authors believe it is an old European disease while others think it is of American origin because the bacteria have been isolated from flying squirrels (13). Epidemic typhus fever has caused more deaths than all of the wars in history (14). In 1909, Charles Nicolle, a French physician, demonstrated that typhus fever is transmitted by lice. Nicolle was awarded the Nobel Prize in Physiology or Medicine in 1928 for his ground-breaking work. The disease is caused by “Rickettsia prowazekii” a bacterium, which is transmitted by lice from infected to healthy humans during feeding. It occurs in a population that suffers from extreme unhygienic conditions and overcrowding. The disease was a major problem in prisons, army camps, and refugee camps, where largenumbers of people were confined in close quarters. Typhus patients begin to feel headache, muscle pain, skin rashes, chills, cough, vomiting, and fever. The history of typhus fever caused by lice dates back to ancient times, with the first recorded outbreaks occurring in Greece in the 5th century BC. The disease was also prevalent during the Roman Empire and was known as “tabardillo” in Spain during the 16th and 17th centuries. During the Grenada War, 20,000 men were missing, 3000 were killed in battle while 17,000 died because of typhus (14). One ofthe disasters caused by typhus fever in history was during the Napoleonic Wars when 550,000 men of the Grand Army marched to Moscow and only 3,000 came back. Around 20-30% of Napoleonic soldiers died of typhus when they were infested with lice in Vilnius, Lithuania (3) (13). In Canada, the “1847 North American typhus epidemic” caused the death of around 20,000 people (15). During world war I and II, millions of people died, and many soldiers, prisoners, and even doctors were infected. In Serbia, at least 150,000 including 50,000 prisoners died from typhus. Today, typhus fever is relatively rare in developed countries, thanks to improved living conditions, better sanitation, and the availability of effective antibiotics. However, the disease remains a major public health problem in many developing countries, particularly in areas where poverty, war, and social upheaval makes it difficult to control the spread of lice and other vectors.
Interesting Fact: Because lice lay eggs at the base of the hair shaft, the eggs distance from the hair shaft can be measured to know when these lice eggs will hatch.
Relapsing fever: From Egyptian mummies to modern-day migrations
Louse-borne relapsing fever or LBRF caused by the bacterium “Borrelia recurrentis” is restricted to one vector,the human body louse (16), and is a fascinating yet deadly disease that has plagued humanity for centuries. It has a history from 550 AD when it frequently lead to jaundice, reported as “Yellow Plague” (13). The evidence of the disease found in Egyptian mummies dating back over 3,000 years is also present. LBRF patients begin to feel pain, dry cough, fatigue, and fever, the death rate is between 10-40 % in untreated patients (10). Factors such as poverty, war, unhygienic conditions, and forced migrations which increase the risk of lice infestation also increased LBRF transmission (16). The name “Relapsing Fever” was first used in 1843 by Craigie (13). During World war I and II, around 1.5 million cases of LBRF were reported with 10% fatalities. In 1919 and 1923, during the Civil wars, 13 million cases were reported, causing 5 million deaths. From 1903 to 1936, there were 50 million cases with 10% mortality in Africa and the Middle East, another epidemic from 1943 to 1946 caused around 10 million cases (16). In 1999-2000, 20,000 cases were reported in South Sudan, and 10,000 cases per year are frequently reported in Ethiopia (13). Since July 2015, LBRF cases are reported in nearly 100 Ethiopian refugees seeking asylum in Germany and Italy (16). In the 20th century, the development of effective insecticides helped to control the spread of LBRF, and the disease became less common in developed countries. However, LBRF remains a major public health problem in many parts of the world, particularly in areas with poor sanitation and hygiene, such as refugee camps and areas of conflict.
Interesting Fact: Don’t worry about your pets – Human head lice can only survive on human blood and cannot live on pets or any other animal.
From the trenches to the present day: The story of Trench Fever
Trench Fever is an old disease caused by the bacterium “Bartonella quintana” which is transmitted by human body louse (10) and has been around for centuries, still managing to pop up in unexpected places. The name “Trench” was chosen because, during World war I, the disease was associated with both German and Allied troops (13). Trench Fever also known as “Five-day fever” due to its short duration, resulted in a high fever, headache, soreness of muscle, and pain on moving eyeballs. Interestingly, the oldest record of the bacterium was found when its DNA was isolated from the remains of a 4000-year-old man. Its DNA was also found in the graves of Napoleon’s soldiers, suggesting they too were affected by this disease (10). John Graham was the person who described Trench Fever in 1915. Trench Fever was imported by German troops in 1914 and spread to Mesopotamia by British soldiers. During the two world wars, it affected more than 1 million people, especially in Europe and Russia (13). After the end of World War I, trench fever became less common in developed countries due to improved living conditions and hygiene, but in the 1990s, it was reported as re-emerging in the residents of developed countries who have poor hygiene conditions, poverty, and exposure to low temperature (10).
Beyond rats and fleas: Did human lice play a role in the devastating Black Death epidemic?
It’s hard to imagine that something as small and seemingly harmless as a flea or louse could cause such devastation, but in the Bronze Age, they were the vectors of one of the most infamous diseases in human history. The role of human lice in the transmission of plague is not fully clear yet (10) but there is some supporting circumstantial and experimental evidence: At the beginning of the 20th century, it was found that head lice were infected with the plague on their own, without any deliberate efforts to infect them. Later on, infected body lice were recovered from the clothes of a plague victim (3). In 2006, it was shown how lice feces can transmit Yersinia pestis (the causative agent of plague). Infected lice feces from skin, enter the body, and then the bloodstream when an individual scratches the lesions at the bite site. Y. pestis was also found in human lice during the endemic outbreaks in Congo. In 2010, two rabbits were experimentally infected with Y. pestis, and 150 uninfected lice were fed on these rabbits for 1 hour. Y. pestis was found in 120 randomly tested lice and in their feces (11). Another experimental model has shown that the human body louse is the potential vector of plague and as few as 10 lice can transmit plague while feeding on the host (12).
Interesting Fact: Humanlice have been living on earth for a very long time: Lice infestation has been found on Egyptian mummies and in medieval European manuscripts.
While the role of human lice in transmitting other pathogens is still debated, recent studies have shown that these tiny creatures could be playing a bigger role in spreading diseases than we previously thought. In fact, a bacterium that causes urinary tract infections has been found in 21% of lice collected worldwide and in 33% of head lice collected from school children in France (10). Lice can transmit any bacterial pathogen which is ingested with blood meal and can survive in the midgut of lice (13). There are only three well known lice-borne diseases: typhus fever, relapsing fever, and trench fever. Typhus fever and relapsing fever are prevalent in the population of developing countries that have poor hygiene conditions, while trench fever is common in the homeless persons of developed countries (10). Preventing lice infestations and maintaining good personal hygiene, such as regular bathing and laundering of clothes and bedding, can help reduce the risk of lice-borne disease transmission. If you suspect that you or someone you know has a lice infestation, it’s important to seek treatment as soon as possible to prevent the spread of lice and the transmission of any potential pathogens they may carry.
References
1. Pedersen MW, Antunes C, De Cahsan B, Moreno-Mayar JV, Sikora M, Vinner L, et al. Ancient Human Genomes and Environmental DNA from the Cement Attaching 2,000-Year-Old Head Lice Nits. 2022;39(2):msab351.
2. Light JE, Smith VS, Allen JM, Durden LA, Reed DLJBEB. Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura). 2010;10(1):1-15.
3. Barbieri R, Drancourt M, Raoult DJTLID. The role of louse-transmitted diseases in historical plague pandemics. 2021;21(2):e17-e25.
4. Reed DL, Light JE, Allen JM, Kirchman JJJBB. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice. 2007;5:1-11.
5. Mullen GR, Durden LA. Medical and veterinary entomology: Academic press; 2009.
6. Fu Y-T, Yao C, Deng Y-P, Elsheikha HM, Shao R, Zhu X-Q, et al. Human pediculosis, a global public health problem. 2022;11(1):58.
7. Barker SCJIjfp. Phylogeny and classification, origins, and evolution of host associations of lice. 1994;24(8):1285-91.
8. Durden LAJM. Biting and sucking lice. 2002:37.
9. Raoult D, Roux VJCid. The body louse as a vector of reemerging human diseases. 1999;29(4):888-911.
10. Badiaga S, Brouqui P. Human louse-transmitted infectious diseases. Clinical microbiology and infection. 2012;18(4):332-7.
11. Ayyadurai S, Sebbane F, Raoult D, Drancourt MJEid. Body lice, Yersinia pestis orientalis, and black death. 2010;16(5):892.
12. Houhamdi L, Lepidi H, Drancourt M, Raoult DJTJoid. Experimental model to evaluate the human body louse as a vector of plague. 2006;194(11):1589-96.
13. Raoult D, Roux V. The body louse as a vector of reemerging human diseases. Clinical infectious diseases. 1999;29(4):888-911.
14. Zinsser H. Rats, lice and history. Boston, USA. 1935.
15. https://www.musee-mccord-stewart.ca/en/. The Governement inspector’s office. 2012.
16. Warrell DA. Louse-borne relapsing fever (Borrelia recurrentis infection). Epidemiology & infection. 2019;147.
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