Louse and Flea Borne Diseases

Louse and flea borne diseases are infections transmitted by lice (predominantly the human body louse and, for certain infections, the human head louse) and fleas. They include the rickettsial typhus infections.

There are additional distinct conditions. Louse borne relapsing fever (Borrelia recurrentis) is transmitted by the human body louse. Plague (Yersinia pestis) is transmitted predominantly by the rat flea. Trench fever (Bartonella quintana) is transmitted by the human body louse.

This group shares a strong association with overcrowding, poor sanitation, homelessness and population displacement, which favour louse and flea infestation and onward transmission.

Pathophysiology and epidemiology

• Louse borne relapsing fever is caused by the spirochaete Borrelia recurrentis. Transmission is through contamination of a louse bite site with infected louse haemolymph, not through the bite itself, since the louse must be crushed for transmission to occur.
• It produces a characteristic relapsing fever pattern. Cyclical antigenic variation allows the spirochaete to evade the host immune response between successive febrile episodes.
• Plague is caused by Yersinia pestis and transmitted predominantly through the bite of an infected rat flea, with the classical sylvatic and urban rat reservoir cycle. It presents in three principal clinical forms.
• Bubonic plague is the commonest form, with characteristic markedly swollen, tender regional lymph nodes, or buboes. The other forms are septicaemic and pneumonic.
• Pneumonic plague, uniquely among these forms, can also be transmitted directly person to person via respiratory droplets. This route carries significant public health and biosecurity implications.
• Trench fever is caused by Bartonella quintana and transmitted by the human body louse. The same organism causes bacillary angiomatosis in significantly immunocompromised patients.
• Trench fever classically produces a relapsing febrile illness with characteristic shin pain. It was historically associated with trench warfare conditions and is now recognised particularly in homeless populations with body louse infestation.

• Louse borne relapsing fever presents with recurrent episodes of high fever, rigors, headache and myalgia. Each episode typically lasts several days and is separated by an afebrile interval of approximately one week. Jaundice and hepatosplenomegaly are common.
• Severe louse borne relapsing fever carries risk of significant complications, including myocarditis and, notably, a Jarisch Herxheimer reaction.
• The Jarisch Herxheimer reaction is an acute, sometimes severe, systemic inflammatory reaction shortly after antibiotic treatment starts. It reflects rapid spirochaete lysis and release of inflammatory mediators, and requires specific anticipation and management.
• Bubonic plague presents with abrupt onset high fever and an intensely painful, rapidly enlarging regional lymph node (bubo). The bubo is typically in the groin, axilla or neck, depending on the site of the flea bite. The overlying skin is often erythematous and warm. Systemic toxicity develops rapidly if untreated.
• Septicaemic plague presents with fever and systemic sepsis without a clinically apparent bubo.
• Pneumonic plague presents with rapidly progressive severe pneumonia, haemoptysis and respiratory failure. It may be a primary presentation from respiratory droplet transmission, or secondary to haematogenous spread from bubonic or septicaemic disease. Mortality is very high without extremely prompt treatment.
• Trench fever presents with recurrent episodes of fever, headache and characteristic severe shin (pretibial) pain. Some cases have a transient maculopapular rash.
• The illness is typically self limiting. Untreated or inadequately treated disease can cause prolonged, relapsing symptoms over weeks to months.

• Louse borne relapsing fever is diagnosed by direct visualisation of spirochaetes on a peripheral blood film examined during a febrile episode, when spirochaetaemia is at its highest. Organism presence follows the cyclical relapsing fever pattern.
• Polymerase chain reaction testing is an increasingly available, more sensitive alternative confirmatory approach.
• Plague diagnosis relies on culture of bubo aspirate, blood, or sputum according to the clinical form. Given the public health urgency, use rapid diagnostic testing (including antigen detection assays) where available.
• Any suspected case of plague requires immediate notification to public health authorities.
• Rapid clinical deterioration is possible, and pneumonic transmission has biosecurity implications. Never delay treatment pending laboratory confirmation in a clinically compatible presentation with relevant epidemiological exposure.
• Trench fever diagnosis follows the same Bartonella specific approach detailed under bacillary angiomatosis and cat scratch disease. The principal modalities are blood culture and polymerase chain reaction testing. Blood culture needs prolonged incubation given the fastidious, slow growing nature of the organism.

• Louse borne relapsing fever is treated with a single dose of doxycycline 100 mg orally, or a short course of tetracycline or erythromycin.
• Treatment is anticipated to provoke a Jarisch Herxheimer reaction in the great majority of patients. The reaction typically occurs within hours of the first antibiotic dose and can be severe. Monitor closely and give supportive management, including careful fluid management and, in severe reactions, haemodynamic support.
• Plague requires immediate treatment given its potential severity and rapid progression. Streptomycin or gentamicin are the historically preferred first line agents. Doxycycline or ciprofloxacin are effective and increasingly used alternatives. Treatment duration is typically ten to fourteen days.
• Strict respiratory isolation precautions are mandatory for suspected or confirmed pneumonic plague, given the risk of person to person respiratory transmission.
• Any suspected case of plague requires immediate notification to public health authorities. This reflects the substantial public health significance, potential for outbreak, and biosecurity considerations.
• Arrange prompt contact tracing. Consider postexposure prophylaxis (typically with doxycycline) for close contacts of confirmed pneumonic plague cases.
• Trench fever is treated with doxycycline, generally for a minimum of four weeks given the risk of relapse with shorter courses. Gentamicin is sometimes added for the initial period in more severe presentations. The principles are broadly similar to other Bartonella associated infections.
• Prevention across this group centres on louse and flea control. This includes delousing measures, and improved sanitation and living conditions. For plague, add rodent and flea control measures in endemic regions.
• Prompt case identification and public health response are needed given the outbreak potential, particularly of pneumonic plague. Louse borne relapsing fever and epidemic typhus have historical significance in situations of population displacement, overcrowding and breakdown of normal sanitation infrastructure.