Rickettsial Zoonoses: Diagnosis, Treatment & Control Measures

Rickettsial zoonoses, a group of vector-borne illnesses caused by Gram-negative obligate intracellular bacteria, are transmitted by ticks, fleas, lice, and mites. The advancement of molecular diagnostic tools has led to the discovery of numerous rickettsial species, making rickettsioses the most common emerging/reemerging zoonoses globally.

Scrub typhus, which causes significant disease burden, remains the most crucial rickettsial infection globally and is predominantly found in the "tsutsugamushi triangle" geographic region. This triangle extends from northern Japan and Eastern Russia in the north to northern Australia in the south and Pakistan in the west and causes almost a million cases annually, with practically a billion individuals at risk.

In this thread, we'll discuss a few selected rickettsial zoonoses, their aetiology, diagnosis, tretment and containment measures.

Summary of Ricketsial diseases and their vectors​

Anaplasma	Human anaplasmosis	Anaplasma phagocytophilum A. platys A. ovis "A. capra"	Tick	Small mammals, rodents, deer Dogs Sheep Goats	Primarily United States, worldwide Venezuela Cyprus, Iran China
Ehrlichia	Human ehrlichosis	Ehrlichia chaffeensis Ehrlichia muris E. ewingii E. canis	Tick	Deer, wild and domestic dogs, domestic ruminants, rodents Dogs	Common in United States, possibly worldwide Venezuela
Neoehrlichia	Neoehrlichiosis	Neoehrlichia mikurensis	Tick	Rodents	Europe, Asia
Neorickettsia	Sennetsu fever, neorickettsiosis	Neorickettsia sennetsu	Trematode (ingestion)	Fish	Japan, Malaysia, possibly other parts of Asia
Scrub typhus	Scrub typhus	Orientia tsutsugamushi	Larval mite (chigger)	Rodents	Asia-Pacific region from maritime Russia and China to Indonesia and North Australia to Afghanistan
Spotted fever	Rickettsiosis	Rickettsia aeschliman- nii	Tick	Unknown	South Africa, Morocco, Mediterranean littoral
African tick-bite fever	R. africae	Tick	Ruminants	Sub-Saharan Africa, West Indies
Rickettsialpox	R. akari	Mite	House mice, wild rodents	Countries of the former Soviet Union, South Africa, Korea, Turkey, Balkan countries, United States
Queensland tick typhus	R. australis	Tick	Rodents	Australia, Tasmania
Mediterranean spotted fever or Boutonneuse fever	R. conorii	Tick	Dogs, rodents	Southern Europe, southern and western Asia, Africa, India
Cat flea rickettsiosis	R. felis	Flea	Domestic cats, rodents, opossums	Europe, North and South America, Africa, Asia
Far Eastern spotted fever	R. heilong- jiangensis	Tick	Rodents	Far East of Russia, Northern China, eastern Asia
Aneruptive fever	R. helvetica	Tick	Rodents	Central and northern Europe, Asia
Flinders Island spotted fever, Thai tick typhus	R. honei, including strain "marmionii"	Tick	Rodents, reptiles	Australia, Thailand
Japanese spotted fever	R. japonica	Tick	Rodents	Japan
Mediterranean spotted fever-like disease	R. massiliae	Tick	Unknown	France, Greece, Spain, Portugal, Switzerland, Siciliy, central Africa, Mali, and Argentina
Mediterranean spotted fever-like illness	R. monacensis	Tick	Lizards, possibly birds	Europe, North Africa
Maculatum infection; Tidewater spotted fever; American boutonneuse fever	R. parkeri	Tick	Rodents	North and South America
Tickborne lymphadenopathy, Dermcentor-borne necrosis and lymphadenopathy	R. raoultii	Tick	Unknown	Europe, Asia
Rocky Mountain spotted fever Brazilian spotted fever	R. rickettsia	Tick	Rodents	North, Central, and South America
North Asian tick typhus, Siberian tick typhus	R. sibirica	Tick	Rodents	Russia, China, Mongolia
Lymphangitis-associated rickettsiosis	R. sibirica mongolotimonae	Tick	Rodents	Southern France, Portugal, China, Africa
Tickborne lymphaden- opathy (TIBOLA), Dermacentor-borne necrosis and lymphaden- opathy (DEBONEL)	R. slovaca	Tick	Lagomorphs, rodents	Southern and eastern Europe, Asia
Typhus fever	Epidemic typhus, sylvatic typhus Murine typhus, fleaborne typhus	R. prowazekii R. typhi	Human body louse, flying squirrel ecto- parasites, possibly some ticksFlea	Humans, flying squirrels Rodents	Central Africa; Asia; Central, North, and South America Tropical and subtropical areas worldwide

Table Source: CDC

 

[Kev]

Q-fever​

• This is a food-borne disease as well as a zoonose. It is common in most parts of the world.
• In animals, it causes abortions and in humans, it causes serious disease. It is a professional hazard for people dealing with livestock and those handling raw animal products.
• Ticks are the main carriers and the pathogen will be found in the aborted material. It is also found in the placenta of cattle, sheep, and goats as well as in milk of these animals.

Aetiology of Q-fever​

It is caused by a rickettsia microorganism Coxiellae burnettii.

Manifestation of Q-fever in animals​

• It is transmitted by tick bites. The sick animals exhibit the following symptoms:
• High rate of abortions at any stage of the pregnancy
• Inapparent / sub-clinical forms are also common in animals. The organism is shed in milk in this form posing danger to the human consumers.

Q-fever in humans​

• People get the disease as a professional hazard when they inhale or contact a sick animal and/or the aborted material.
• Consuming contaminated milk and milk products is also a route of transmission.
• Human to human transmission has not been recorded. However, the organism has been extracted from milks of mothers who have recovered from the disease.

Symptoms of Q-fever in humans​

Incubation period lasts 2 – 4 weeks. Observable symptoms include:

1. Sudden onset of influenza (flu) like syndrome (e.g. high fever, general malaise, weakness, depression, anorexia). This then progresses to,
2. Dry cough
3. Chest pain and dyspnoea due to pneumonia
4. Jaundice since the liver is affected
5. Fatality rates are very low. People recover after administration of drugs.

Diagnosis of Q-fever​

• Do serological tests for confirmation of the organism.
• Isolate the microorganism from the aborted material.

Control measures for Q-fever​

1. Effective tick control
2. Proper pasteurization of milk
3. Wear personal protective gear while handling animals and animal products and byproducts
4. Proper disposal of aborted material.

Other rickettsial zoonoses include:​

1. Epidemic typhis
2. Murine typhis
3. Rocky Murine typhis
4. Spotted fever

Typhis fever affect both humans and animals, especially dogs. They are transmitted by ticks and fleas.
Dogs and monkeys do not get serious disease.
In humans, the patient may experience high fever, joint pains, muscle pain, swellings at the bite sites that may progress into ulcers.
Lymph nodes that are proximal to the bite site will swell.
Spontaneous recovery usually occur.