Typhus and Other Rickettsial Diseases

Causative agent

Rickettsial diseases are caused by multiple bacteria known as ‘rickettsiae’. They are classically divided into the spotted fever group and typhus group; and the typhus group can be further categorised into scrub typhus, urban typhus, and epidemic typhus. In Hong Kong, scrub typhus and spotted fever are the most common types of rickettsial diseases, followed by urban typhus, while epidemic typhus has not been reported locally in the past few decades.

Clinical features

Rickettsial diseases commonly present with non-specific symptoms similar to a bad cold, including fever, chills, headache, muscle pains and rash. Scrub typhus and spotted fever are characterised by a punch-out skin ulcer at the site of bite of an infected arthropod. Nearby lymph nodes can also become swollen and painful. In severe cases, rickettsial diseases can result in severe complications and even death.

Mode of transmission

Rickettsial diseases are mainly transmitted through vectors such as mites, fleas, lice and ticks. Different types of rickettsial diseases are transmitted by different types of vectors.

Scrub typhus (also known as tsutsugamushi disease)

• Humans are infected through the bites of infected mites that mainly feed on the body fluid of animals such as rats in scrubby areas.

Urban typhus (also known as endemic typhus or murine typhus)

• Humans are infected when the faeces of infected fleas get into breaks in the skin or mucous membranes. The fleas mainly live on rats and cats. Infection can also occur when dried faeces of infective fleas are inhaled.

Epidemic typhus

• Humans are infected when the crushed tissues or faeces of infected lice get into breaks in the skin or mucous membranes. The lice can live on human body. Infection can also occur when dried faeces of infective lice are inhaled.

Spotted fever

• Spotted fever is mainly transmitted through the bites of infected ticks found in habitats where there are dense vegetation and suitable host animals. Dogs and rats may carry ticks on their bodies. Infection can also occur when crushed tissues or faeces of the infected ticks get into breaks in the skin or mucous membranes.

Incubation period

The incubation period for scrub, urban, and epidemic typhus is commonly 7 – 14 days (may be up to 3 weeks), while that of spotted fever is 6 – 15 days.

Management

Treatments for most rickettsial illnesses are similar. Appropriate antibiotics should be prescribed along with supportive care.

Prevention

The vectors transmitting scrub typhus and spotted fever are mainly found in vegetated areas; preventive measures should be taken when visiting rural areas to avoid being bitten by these vectors.

Pre-visit preparation:

• Wear loose, light-coloured, long-sleeved tops and trousers
• Wear shoes that cover the entire foot, avoid wearing sandals or open shoes
• Tuck trousers into socks or boots to prevent arthropods from reaching the skin
• Use DEET-containing insect repellent on exposed parts of the body and clothing
  • Pregnant women and children of 6 months or older can use DEET-containing insect repellent.
• Avoid using fragrant cosmetics or skin care products
• If both insect repellents and sunscreen are used, apply insect repellents after sunscreen

During the visit:

• Stay on footpaths and avoid walking through vegetation. Do not brush along the vegetation at the sides of footpaths
• Avoid resting on vegetation, or at humid and dark places
• Do not hang clothing on trees or vegetation
• Do not feed wild or stray animals
• Re-apply insect repellents according to instructions

After the visit:

• Inspect body parts and clothing. Clear any attached arthropods carefully
• Take a soapy shower and wash the clothes
• Inspect and clean the bodies of accompanying pets

If an attached tick is found on the body:

• Gently remove it by grasping its head with tweezers or fine-tipped forceps close to the skin, then disinfect the bite area and wash hands with soap and water
• Do not crush or twist the tick during removal

Control of vectors and the reservoir of the diseases are also useful preventive measures:

• Disinfest your pets regularly
• Inspect and disinfest pet beddings regularly
• Trim vegetation particularly the grass in your premises
• To prevent rat infestation, the best method is to deprive their food and shelter. Store food and dispose of garbage properly. Holes at the wall and ceiling should be repaired and filled

Besides, maintaining good personal hygiene is effective to prevent the spread of epidemic typhus as lice can live on the human body.

For details about the use of insect repellents and the key points to be observed, please refer to 'Tips for using insect repellents'.