17th June 2024

Rabies & Leprosy

Rabies

Rabies, caused by a virus of the Lyssavirus genus, is a fatal disease of the central nervous system if given time to propagate. It is transmitted through direct contact with infected mammals, often a bite. These mammals include dogs, bats, and raccoons. The first symptoms of rabies infection are a flu-like illness and irritation at the site of the bite. There is generally a long incubation period between exposure and CNS symptoms – in the order of weeks – as it takes time for the virus to travel backwards through peripheral nerves. This is shortened in children or in bites to the face as there is a smaller distance to travel. CNS symptoms include fluctuating periods of confusion, severe agitation and aggression. Other symptoms include hypersalivation and hydrophobia. The disease is almost always fatal once CNS symptoms are present.

Rabies is a vaccine-preventable disease. Post-exposure prophylaxis, involving a combination of vaccinations and immunoglobulins, is also available. As rabies is generally a disease of resource-poor areas, a patient may choose to observe a dog after a potential transmission event instead of immediately seeking medical attention. If the dog remains alive and well after around 10-15 days, then it did not have transmissible rabies infection at the time of the direct contact. As alluded to, this method may be risky if the incubation period is expected to be shorter than usual. The vaccination schedule and use of immunoglobulin therapy depends on whether it is pre-or post-exposure prophylaxis, as well as previous vaccinations, local endemicity of rabies, and severity of exposure. Please see the Green Book reference for further details and note that these are always subject to change.

Leprosy

Leprosy is caused by Mycobacterium leprae and has an almost worldwide distribution, with an incidence of over 100,000 cases per year. It is primarily a disease that affects the skin and peripheral nerves and is contracted through prolonged contact with an untreated individual. Blindness is a potential consequence of the disease.

Diagnosis of leprosy can be made clinically, with findings of stereotypical skin lesions and thickened peripheral nerves. A clinical spectrum exists between paucibacillary leprosy (tuberculoid) and multibacillary leprosy (lepromatous). Multibacillary leprosy is a failure of the cell-mediated immune response to the mycobacteria. This results in more lesions, more affected nerves, and more mycobacteria on skin snippings. Individuals with paucibacillary leprosy will have full anaesthesia over a fewer number of skin lesions, which will be asymmetrically distributed. Bacterial load can be calculated by microscopy of skin scrapings. Treatment regimens are based on whether the clinical picture is one of multibacillary or paucibacillary leprosy. Rifampicin, dapsone and clofazimine are used in combination for multibacillary leprosy, whereas a shorter course of rifampicin and dapsone alone is sufficient to treat paucibacillary leprosy. Steroids are used if new nerve damage is present on routine follow-up or if there is evidence of hypersensitivity or immune complex-mediated reactions at any point before, during, or after antimicrobial treatment.

References

• Rupprecht CE, Mani RS, Mshelbwala PP, Recuenco SE, Ward MP. Rabies in the Tropics. Curr Trop Med Rep. 2022;9(1):28-39. doi: 10.1007/s40475-022-00257-6
• Solomon T, Lalloo D. Rabies. In: Beeching N, Gill G, ed. by. Tropical Medicine Lecture Notes. 7th ed. West Sussex: Wiley Blackwell; 2014. p. 254-258
• UK Health Security Agency. Immunisation against infectious disease. Ramsay M ed by. 2021, Jan
• WHO rabies factsheet [Internet]. WHO.int [cited September 2022]. Available from: https://www.who.int/newsroom/fact-sheets/detail/rabies
• Maymone M, Laughter M, Venkatesh S et al. Leprosy: Clinical aspects and diagnostic techniques. J Am Acad Dermatol. 2020;83(1):1-14. doi: 10.1016/j.jaad.2019.12.080. Epub 2020 Mar 27
• Lockwood D, Beeching N. Leprosy. In: Beeching N, Gill G, ed. by. Tropical Medicine Lecture Notes. 7th ed. West Sussex: Wiley Blackwell; 2014. p. 163-174
• Maymone MBC, Laughter M, Venkatesh S, Dacso MM, Rao PN, Stryjewska BM, Hugh J, Dellavalle RP, Dunnick CA. Leprosy: Clinical aspects and diagnostic techniques. J Am Acad Dermatol. 2020 (1):1-14. doi: 10.1016/j.jaad.2019.12.080
• WHO leprosy factsheet [Internet]. WHO.int [cited September 2022]. Available from: https://www.who.int/newsroom/fact-sheets/detail/leprosy