Diagnostic approach of fever due to zoonotic diseases in the rural population

ACHAIKI IATRIKI | 2023; 42(1):40–44


Maria Lagadinou1,2,3, Georgios Eleftherakis1, Dimitris Papageorgiou1, Themistoklis Paraskevas1, Markos Marangos1,2

1Department of Internal Medicine, University Hospital of Patras, Patras 26504, Greece
2Division of Infectious diseases, University Hospital of Patras, Patras 26504, Greece
3Department of Nursing, University of Patras, Patras 26334, Greece

Received: 12 Apr 2022; Accepted: 04 Oct 2022

Corresponding author: Maria Lagadinou, Assistant Professor of Internal Medicine, Department of Nursing, University of Patras & Department of Internal Medicine, University Hospital of Patras, Greece, E-mail: m_lagad2004@yahoo.gr

Key words: Rural areas, leptospirosis, brucella, West Nile, Q fever, leishmaniasis



Fever is frequent among people living in rural areas. Among others, zoonotic diseases are included in the differential diagnosis. Brucellosis is a disease of zoonotic origin affecting humans in several regions, with the highest impact in regions where productive animals constitute a significant income source. Leptospirosis is a zoonosis with global distribution and is considered as an emerging public health problem. Q fever is a worldwide zoonotic infection, caused by Coxiella burnetii. Leishmaniasis is a zoonosis and the parasite is transmitted by the bite of an infected female phlebotomine sand fly. West Nile is a zoonosis with multiple clinical manifestations. The aim of this review is to provide a general overview of the diagnostic approach of fever in people living in rural areas.


Febrile conditions are frequent among people living in rural areas. Among other illnesses, the most frequently diagnosed diseases in both rural and urban populations are zoonotic diseases.

Zoonotic diseases are diseases that can be transmitted naturally between vertebrate animals and humans. Such zoonoses can be transmitted either directly from animals to humans, or indirectly via food or the environment. Diseases that can be transmitted indirectly via the environment, such as leptospirosis and hantavirus disease, are particularly challenging to control as the natural environment also acts as a reservoir [1].

This article provides a general overview of the diagnostic approach of fever in people living in rural areas (Table 1). Adequate training of health workers is urgently needed since early diagnosis and proper treatment are critical.

Brucellosis: Epidemiology, clinical symptoms and diagnosis

Brucellosis is a zoonotic disease affecting humans in several regions, with the highest impact in regions where productive animals constitute a significant income source. Among other countries of the Mediterranean basin, Greece is considered to be a country endemic for brucellosis with an enormous impact on livestock production, public health and, by extension, to the economy [2]. For the decade 2010-2019 the average annual incidence of cases in Greece was 1.02 cases per 100,000 population.

Brucella species are Gram-negative, small coccobacillus, intracellular bacteria that affect macrophages, dendritic cells, placental trophoblasts, and epithelial cells. Brucella species can survive under extreme conditions of temperature, humidity, pH, and survive in frozen and aborted materials for longer durations [3].

In humans, brucellosis is caused by B. melitensis, B. abortus and B. suis which are transmitted by infected goats, pigs, sheep or cows to healthy humans. Exposure of humans to infected domestic animals or the consumption of milk or meat products derived from infected animals enhances the risk of acquiring brucellosis. The main source of Brucella infection in the urban population is usually contaminated food, milk or dairy products derived from infected animals. Farmers, farm laborers, animal attendants, shepherds, and veterinarians are at a higher risk of infection with Brucella spp. due to direct contact with infected animals or constant exposure to contaminated environments [3].

The main clinical symptoms of brucellosis in humans include intermittent fever, headache, backache, weakness, weight loss, anorexia and mental depression. Complications may occur in the gastrointestinal, cardiovascular, pulmonary, lymphatic, and nervous system. The involvement of the nervous system is termed neuro-brucellosis, and is characterized by fever, headache, psychosis, seizures, and behavioral changes [3,4].

The diagnosis of human brucellosis relies on three different modalities: culture, serology, and nucleic acid amplification tests (NAATs) [5]. The serological method, culture-based method, and molecular techniques are employed to detect Brucella infection in animals and humans. The detection of the microorganism in blood cultures makes it possible to confirm the presence of the disease in its early stages, when the serological tests results are still negative or show low or borderline antibody titers [5].

The routine method for the diagnosis of brucellosis includes the Wright test as the first screening test. The rose bengal test (RBT) is a card agglutination test that uses an 8% suspension of killed B. abortus strain 1119-3 cells stained with rose bengal dye and buffered to pH 3.65 ± 0.05. The RBT detects agglutinating and non-agglutinating antibodies and does not have the drawback of the prozone phenomenon [5]. PCR assay can be applied with serology for the diagnosis of brucellosis suspected cases and relapses regardless of the duration or type of the disease without relying on blood cultures, especially in chronic cases [4].

Leptospirosis: Epidemiology, clinical symptoms and diagnosis

Leptospirosis is a zoonotic disease with global distribution and is considered an emerging public health problem. Spirochaetes of the genus Leptospira account for the disease’s clinical manifestations. All recognized species of Leptospira are categorized into 24 serogroups and 250 serovars based on the expression of surface-exposed lipopolysaccharide [6].

Leptospirosis is highly prevalent in the tropics, with 73% of cases occurring in this zone. It is common among rural farming populations and impoverished urban and semi-urban populations, particularly affecting young male adults. Farmers, those in contact with livestock, those exposed to rodents at their workplace, and people living in areas where sanitation is poor are at higher risk [7]. According to the Greek National Public Health Organisation (GNPHO), approximately 20 cases are reported annually and the incidence varies from 0.13 to 0.31 per 100,000 population depending on the geographical region of the country with seasonal variation [6].

Leptospirosis in humans can range from a mild, self-limiting acute febrile illness to a severe, life-threatening disease with multiple organs failure. Many organ systems can be involved, to varying degrees [7]. The initial ‘leptospiraemic phase’ lasts for three to nine days, and presents with non-specific symptoms: fever, chills, myalgia, and headache. Conjunctival suffusion is a characteristic finding, developing on the third to fourth day. Myalgia can be severe, and can usually involve the calf, abdomen (mimicking acute abdomen) and paraspinal muscles (resulting in meningism) [7].

The ‘leptospiraemic’ or ‘septicaemic’ phase is followed by an immune phase, where IgM antibodies appear in the blood, and organisms are excreted in the urine. A more severe form of the disease consists of conjunctival suffusion, jaundice, and acute kidney injury (Weil’s syndrome). Pulmonary haemorrhage has recently been shown to be an important cause of mortality.

The ‘gold standard’ test currently available for the diagnosis is microscopic agglutination test (MAT), but it does not permit early diagnosis because it relies on detection of antibodies and cannot detect infection until 5–7 days after exposure [7]. Extremely helpful for the diagnosis are: a four-fold rise in MAT titers within a 2–3-week interval and also other assays such as PCR, culture, and immunofluorescent. Isolation of the organism from urine or tissues of the animals is the most reliable method to confirm infection due to Leptospira [6,7].

Q fever: Epidemiology, clinical symptoms and diagnosis

Q fever is a worldwide zoonotic infection, caused by Coxiella burnetii. Q fever infects a variety of hosts, including humans, ruminants (cattle, sheep, goats), pets, and, rarely, reptiles, birds, and ticks. Humans are exposed to the disease as other animals shed the organism in feces, urine, milk, and products of conception. These products contain large numbers of bacteria that become aerosolized after drying and remain virulent for months [8].

Acute Q fever has a wide spectrum of clinical manifestations. Clinical manifestations range from asymptomatic seroconversion, acute disease (ranging from a flu-like syndrome to severe pneumonia), or chronic disease (manifesting mainly as endocarditis or hepatitis) [9]. Most patients (50%-60%) who are infected with Q fever are asymptomatic. Acute Q fever is a self-limited disease in many cases, and even when clinical treatment is recommended, it resolves without adverse sequelae in most patients.

The most frequent presentation is a flu-like illness manifested by fever, sweats, cough (productive at times), myalgias, and arthralgias. A high percentage of patients also have pneumonia and hepatitis [8]. Endocarditis, the most common form of chronic Q fever (60%-70%), represents 3% to 5% of all endocarditis cases. Patients with both acute and chronic disease can have hepatosplenomegaly and hepatitis.

The diagnosis of Q fever relies mainly on serologic examination. Several laboratory studies are available, but antibody detection by immunofluorescence assay is the most commonly used method because of its high sensitivity and specificity. The most widely used serologic test is the detection of phase I and II antibodies. A titer of 200 or greater for IgG and 50 or greater for IgM against phase II antibodies indicates a recent Q fever infection; an IgG titer of 800 or greater against phase I antibodies suggests chronic infection [8,9]. These cutoffs vary among laboratories and defined cutoffs for each individual test should be used [8]. Polymerase chain reaction, a promising test that may even be able to detect the presence of C. burnetii early in disease, is limited to reference laboratories and research studies.

Leismaniasis: Epidemiology, clinical symptoms and diagnosis

Leismaniasis is a vector-borne infectious disease, caused by the genus Leishmania. It is a zoonosis and the parasite is transmitted by the bite of an infected female phlebotomine sand fly. It is among the deadliest neglected tropical diseases, afflicting nearly 700,000 to 1 million people annually [10]. The disease is endemic in tropical and subtropical regions.

Clinically, it is subdivided into visceral (kala-azar), cutaneous and mucocutaneous forms. Visceral leishmaniasis (VL), the most severe form, is a disseminated intracellular protozoan infection that targets tissue macrophages in the liver, spleen and bone marrow [11]. Leishmanial disease causes three main human syndromes: 1. cutaneous disease presents as singular ulcerative or nodular lesions at or near the site of insect exposure. These are usually found on uncovered areas of the body such as the face, forearms and lower legs and evolve over weeks to months, 2. Mucocutaneous disease, an infection resulting from the chronic local destruction of tissue of the nose, mouth oro- and nasopharynx and eyelids. It can progress to affect respiratory function and hamper nutrition 3. Visceral leishmaniasis (VL) results from the infection of phagocytes within the reticuloendothelial system due to the metastasis of parasites and parasite-infected macrophages from the initial site of cutaneous infection [12].

Leishmania infantum can both cause VL, but L. infantum is the predominant pathogen in Mediterranean countries. Laboratory diagnosis of VL includes microscopic observation and culture from adequate samples, antigen detection, serological tests, and detection of parasite DNA [13]. Definitive diagnosis is supported by direct demonstration of parasites in clinical specimens and specific molecular methods. PCR protocols to detect Leishmania DNA in VL diagnosis have used a variety of samples, including spleen, lymph node, and bone marrow aspirates, whole blood, and buffy coat [13].

The culture of the parasite can improve diagnostic sensitivity, but is time- consuming, and expensive, and thus seldom used for clinical diagnosis. ELISA is the preferred    laboratory test for serodiagnosis of VL. This technique is highly sensitive, but its specificity depends upon the antigen used. Moreover, this assay can be performed easily [13].

West Neil Fever: Epidemiology, clinical symptoms and diagnosis

West Nile virus (WNV) is 1 of more than 70 viruses of the family Flaviviridae of the genus Flavivirus. Serologically, West Nile virus is a member of the Japanese encephalitis serocomplex, which includes Japanese encephalitis virus and an endemic North American flavivirus, St Louis encephalitis virus [14]. Mosquito bites are responsible for nearly all human infections. West Nile virus can also be transmitted via transfused platelets, red blood cells, and fresh frozen plasma as well as through heart, liver, lung, and kidney transplants. Transmission via organ transplant has occurred from donors without detectable viremia, suggesting viral sequestration in organs shortly after viremia has cleared [14].

The incubation period for clinical symptoms ranges from 2 to 14 days, but prolonged incubation periods of up to 21 days have been observed among immunocompromised patients. Following the incubation, 75-80% of infected persons may remain asymptomatic. About 20-25% of infected patients typically experience the abrupt onset of fever, headache, fatigue and myalgias. Gastrointestinal complaints, including nausea and vomiting, have been frequently described [15]. West Nile meningitis, is characterized by the abrupt onset of fever and headache along with meningeal signs and photophobia. West Nile Encephalits (WNE) may range in severity from a mild, self-limited confusional condition to severe encephalopathy, coma and death. This manifestation is more commonly seen in older individuals, particularly over the age of 55, as well as immunocompromised persons [14].

Because the virus is present at very low levels in human blood and tissues, real-time PCR-based detection systems are recommended for the rapid detection of WNV infection in clinical samples [16]. Following exposure to WNV, both IgM and IgG antibodies are produced. In most cases, IgM antibodies can be detected within 4 to 7 days after the initial exposure and may persist for more than one year. In contrast, anti-WNV IgG are reliably detected approximately 8 days after the onset of symptoms and they have a limited use in the initial diagnosis of WNV infection [16].

The management of patients with WNV encephalitis or encephalomyelitis is a challenging problem since there is currently no definitive treatment for WNV infection. The prevention of infection through protection from mosquito bites is therefore critical and the single most important public health measure. The management of illness due to WNV infection remains supportive. Patients with otherwise uncomplicated WNV infection generally do not require specific intervention. Patients with severe WN infection require symptomatic therapy such as pain control for severe headache.

Conflict of interest disclosure

None to declare

Declaration of funding sources

None to declare

Author Contributions

ML, GE, DP, TP literature search & manuscript drafting; ML critical revision of the article for important intellectual content; MM final approval of the article.


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