17th June 2024

Other tropical infections

The tropical bowel

Tropical sprue

Tropical sprue is a disease of unknown aetiology occurring in tropical and subtropical countries, though it is relatively less common on the African continent. It is characterised by malabsorption in the small bowel. It is often precipitated by an acute diarrhoeal illness. Villous blunting is observed on endoscopy. A prolonged course of antibiotics is given as treatment for the associated bacterial overgrowth, as well as nutrition supplementation, and there is usually a good resolution of pathology.

Giardiasis

The protozoan infection Giardiasis, caused by Giardia duodenalis, is spread via the faecal-oral route and has a worldwide distribution. The incubation period is generally several days but can extend into weeks and months. Signs and symptoms include foul-smelling diarrhoea and flatulence, abdominal pain, and weight loss if there is any chronicity. Stool microscopy is generally used to make a diagnosis and the treatment is a course of metronidazole.

Rickettsial infection

Rickettsial disease refers to infection caused by intracellular bacteria of the family Rickettsiaceae. All these diseases present with a typical triad of fever, arthralgia, and rash. Louse-borne – epidemic – typhus occurs when Rickettsia prowazekii is transmitted through the infected faeces of the human body louse via the skin. It is associated with areas of poor hygiene, such as refugee camps, and can cause multi-organ inflammation and failure, with a high mortality rate if left untreated. Tick typhus, including Rocky Mountain spotted fever and African tick typhus, have varying clinical courses. There is usually an eschar present with African tick typhus, and it is generally less severe than Rocky Mountain spotted fever. Finally, scrub typhus, caused by Orientia tsutsugamushi, is transmitted via biting mites from Eastern Asia and Oceania. A small eschar can be found at the site of the bite, with hepatosplenomegaly and multi-organ dysfunction possible sequalae. Rickettsial disease is generally susceptible to tetracycline antibiotics.

Anthrax

Anthrax, caused by the endospore-forming Bacillus anthracis, is classified by route of inoculation. Cutaneous and inhalational anthrax generally occurs after occupational exposure to spores from animal products. Bioterrorism may also be alluded to in single best answer questions. Consumption of contaminated meat leads to gastrointestinal anthrax. Injectable anthrax can result from injecting contaminated illicit drugs. Cutaneous anthrax has a short incubation period and generally resolves over a few weeks with appropriate treatment, though it can lead to fatal sequalae in 20% of untreated patients. The lesion typically contains a central dark eschar with significant surrounding oedema. Inhalational anthrax presents with upper respiratory tract symptoms followed by swift respiratory failure and death. Gastrointestinal anthrax presents with severe abdominal pain and bloody diarrhoea, followed often by overwhelming sepsis. All forms may rarely be complicated by meningeal spread. Diagnosis of cutaneous anthrax is made by microscopy of fluid from the lesion, with PCR if necessary. Blood cultures are also a vital investigation. Cutaneous anthrax may be treated with ciprofloxacin, doxycycline, or, when sensitivities are known, amoxicillin. Therapy for other forms is more complicated, with benzylpenicillin often part of the antimicrobial cocktail. Inhalational and gastrointestinal forms of anthrax are likely fatal, even with appropriate treatment.

Plague

Plague, caused by the bacteria Yersinia pestis, is generally transmitted by fleas and can present in three forms. Bubonic and septicaemic plague is what is classically depicted in images from the 14th century pandemic. Bubonic plague is characterised by fever, malaise, and the appearance of buboes; painful, swollen lymph nodes. Septicaemic plague is characterised by shock and tissue necrosis – “black death”. Pneumonic plague, which can be transmitted from person to person via respiratory droplets or develop from untreated bubonic or septicaemic plague, is associated with a rapidly progressive multilobar consolidative process. Buboes can be sampled for diagnosis, or samples of sputum or blood can be analysed. A variety of classes of antibiotic are used as treatment. Post-exposure antibiotic prophylaxis is recommended after contact with pneumonic plague. A vaccine exists for individuals expected to be at high risk of the disease, such as exposed healthcare workers and clinical scientists.

Other tropical infections

There are several other tropical infections which can come up in part 2 of MRCP, including bacterial gastroenteritis, leptospirosis, Q fever, and melioidosis. It is worth having some familiarity with the pertinent features of each of these.

References

• Stein C, Parry C, Frean J et al. Multi-system diseases and infections. In: Davidson R, Brent A, Seale A, ed. by. Oxford Handbook of Tropical Medicine. 4ᵗʰ ed. Oxford: Oxford University Press; 2014. p. 729-822
• Price E, Seymour M, Sarovich D et al. Molecular epidemiologic investigation of an anthrax outbreak among heroin users, Europe. Emerg Infect Dis. 2012;18(8):1307-13. doi: 10.3201/eid1808.111343
• Blanton L. Rickettsial infections in the tropics and in the traveller. Curr Opin Infect Dis. 2013;26(5):435-40. doi: 10.1097/QCO.0b013e328363811b
• Penny M, Rivera F. Diarrhoeal diseases. In: Davidson R, Brent A, Seale A, ed. by. Oxford Handbook of Tropical Medicine. 4ᵗʰ ed. Oxford: Oxford University Press; 2014. p. 233-292