What is Lassa fever
Lassa fever is an acute infectious disease caused by the Lassa virus, primarily transmitted through rodents. It is mainly prevalent in West African countries, including Nigeria, Liberia, Sierra Leone, and Guinea.
Lassa fever is named after the town of Lassa in northeastern Nigeria, where it was first identified. In 1969, healthcare workers in this town encountered the disease, marking the first known cases of the hemorrhagic fever caused by the Lassa virus, and the illness was named after the location of its discovery.
Transmission Sources and Host Animals
The primary reservoir and transmission source of the Lassa virus in nature are rodents, predominantly the Mastomys natalensis (multimammate rat), along with other species such as the black rat (Rattus rattus) and African pygmy mouse (Mus minutoides). Interestingly, Mastomys natalensis can harbor the Lassa virus without showing symptoms, exhibiting a high rate of chronic asymptomatic infection. The virus is excreted through the saliva and urine of these rodents, which can contaminate food and water sources .
This asymptomatic nature of the multimammate rat plays a crucial role in the transmission of the virus, as it allows the rodents to live and thrive in close proximity to human populations without obvious signs of infection. As a result, human exposure to the virus often occurs indirectly through contaminated environments or direct contact with these rodents and their excretions .
Transmission Routes
- Direct Contact: Individuals can become infected if the virus enters through broken skin or mucous membranes after direct contact with contaminated materials, such as rodent droppings .
- Environmental Contamination: Foods or surfaces contaminated with rodent excretions can also pose a risk for infection when ingested .
- Human-to-Human Transmission: The Lassa virus can spread between humans, particularly in settings like hospitals or during care for infected patients, where bodily fluids can come into contact with broken skin or mucous membranes.
- Healthcare and Laboratory Infections: There is a risk of infection in healthcare settings and laboratories, where strict adherence to infection control practices is crucial to prevent outbreaks .
Clinical Manifestations
Lassa fever can present with a variety of symptoms that may initially seem nonspecific, making self-diagnosis difficult for the general public. Common symptoms include:
- General Discomfort: Patients often experience a feeling of overall malaise.
- Fever: High fever is typically one of the first indicators of the disease.
- Sore Throat and Cough: Patients may report throat pain along with a dry cough.
- Nausea and Vomiting: Gastrointestinal symptoms can also occur, including nausea and vomiting.
- Diarrhea: Some individuals may experience diarrhea, which can lead to dehydration.
- Muscle Pain: Myalgia is a frequent complaint among infected individuals.
- Chest and Abdominal Pain: Discomfort or pain in the chest and abdomen may also occur  .
Pregnancy Complications
Lassa fever can be particularly severe during pregnancy, posing significant risks to both the mother and the fetus. The majority of pregnant women infected with the virus may experience complications such as miscarriage  .
This highlights the importance of early diagnosis and medical intervention for pregnant women who may have been exposed to the virus. Supportive care is crucial for managing symptoms and reducing risks.
Epidemiological Characteristics
Lassa fever exhibits distinct epidemiological characteristics, particularly in its prevalence and transmission patterns in West Africa. Here are some key features:
- Geographic Distribution: Lassa fever is primarily endemic in West African countries, notably Nigeria, Sierra Leone, Liberia, and Guinea. The disease is closely associated with areas where the Mastomys natalensis rodent is common  .
- Seasonality: The incidence of Lassa fever can be seasonal, often peaking during the dry season when food scarcity may lead to increased rodent-human interactions as people store food .
- Human Infection Rates: The majority of human infections occur in rural and peri-urban areas, where there is a higher likelihood of contact with infected rodents. Healthcare workers are at increased risk of infection, particularly if protective measures are not observed  .
- Asymptomatic Cases: A significant proportion of cases are asymptomatic or mild, which complicates control efforts. Infected individuals may not seek medical attention, allowing for continued transmission  .
- Mortality Rates: The mortality rate of Lassa fever varies but can be as high as 15% in severe cases. Pregnant women are particularly vulnerable, with higher rates of miscarriage and severe outcomes  .
How to take care of yourself
- Avoid Rodent Exposure: Implement measures to reduce rodent populations in and around your home. This includes keeping food stored securely, sealing holes in walls, and maintaining cleanliness to discourage rodent infestation.
- Hygiene Practices: Regularly wash your hands with soap and water, especially after handling food or coming into contact with potentially contaminated surfaces or materials.
- Food Safety: Be cautious about food preparation. Avoid eating food that might be contaminated by rodents, and ensure that all food is properly cooked.
- Health Monitoring: If you experience symptoms like fever, fatigue, or gastrointestinal issues after potential exposure to rodents or in endemic areas, seek medical attention promptly.
- Awareness and Education: Stay informed about Lassa fever and its risks, especially if you live in or travel to areas where the disease is endemic. Awareness can help in early detection and prevention.
- Protective Measures in Healthcare: For healthcare workers, use personal protective equipment (PPE) when caring for patients with suspected Lassa fever to prevent human-to-human transmission  .