Lassa Virus!

What causes Lassa fever?

The reservoir, or host, of Lassa virus is a rodent known as the "multimammate rat" of the genus Mastomys. It is not certain which species of Mastomys are associated with Lassa; however, at least two species carry the virus in Sierra Leone: M. huberti and M. erythroleucus. Mastomys rodents breed very frequently, produce large numbers of offspring, and are numerous in the savannas and forests of West, Central, and East Africa. In addition, some species, like M. huberti, prefer to live in human homes. All these factors together contribute to the relatively efficient spread of Lassa virus from infected rodents to humans.

Tests and diagnosis discussion for Lassa fever:

Lassa fever is most often diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA), which detect IgM and IgG antibodies as well as Lassa antigen. The virus itself may be cultured in 7 to 10 days. Immunohistochemistry performed on tissue specimens can be used to make a post-mortem diagnosis. The virus can also be detected

Routine studies include a CBC, sedimentation rate, chemistry panel, urinalysis, chest x-rays, VDRL test, and tuberculin skin test. Serial blood cultures should be done on all patients. Febrile agglutinins usually should be done. An ASO titer or streptozyme test should be done to exclude rheumatic fever. RNA, ANA, and DNA tests should be done to look for lupus and other connective tissue disease. An HIV antibody titer may need to be ordered.

The next step is to culture any discharge or various body fluids that might be suspect. Thus, a urinalysis and urine culture should be done. A nose and throat culture should be done. A sputum smear and culture may need to be done. The next consideration is to do various serologic tests. A heterophile antibody titer should be done in teenagers. Febrile agglutinin tests may need to be done. Acute and convalescent phase sera for viral studies may need to be done.

Next one should do skin testing. Thus, histoplasmin, coccidioidin, and blastomycin skin testing should be done on patients with a cough. Trichinella skin testing may need to be done, as well as brucellin skin testing. A Kveim test might need to be done for suspected sarcoidosis.

The next step is to do plain x-rays of suspected areas. For instance, x-rays of the teeth may disclose an abscessed tooth. X-rays of the long bones may disclose a metastatic carcinoma.

The next step is contrast x-ray studies of various organ systems. An intravenous pyelogram may show a hypernephroma. A cholecystogram may show gallstones. An upper GI series and barium enema may show chronic pancreatitis or diverticulitis. Angiography may disclose periarteritis nodosa, aortitis or giant cell arteritis.

The next step is to do a CT scan of the abdomen and pelvis. If this is negative, consider a CT scan of the chest and mediastinum. Echocardiography may disclose valvular vegetations or an atrial myxoma.

Next, consider biopsying various organ systems. For instances, a lymph node biopsy may disclose a lymphoma or sarcoidosis. A muscle biopsy may disclose periarteritis nodosa, polymyositis, or trichinella.

Next one should do bone scans and gallium scans for possible metastasis, osteomyelitis, or localized abscesses.

If all these procedures fail to turn up a lesion, then an exploratory laparotomy may need to be done. A fibrin test may indicate Mediterranean fever, or urine for etiocholanolone may also indicate a relapsing type of fever. A urine test for porphobilinogen may diagnose porphyria.

The wisest move is to conduct this investigation with the help of an infectious disease specialist or a specialist in the body organ system most likely suspected of harboring the infection.

by reverse transcription-polymerase chain reaction

Symptoms:

Lassa fever is an acute viral illness caused by Lassa virus, which is hosted by rodents in the Mastomys natalensis species complex and rarely imported to countries outside of those areas in Africa where the disease is endemic (1). Lassa fever is characterized by fever, muscle aches, sore throat, nausea, vomiting, and chest and abdominal pain. Approximately 15%--20% of patients hospitalized for Lassa fever die from the illness; however, approximately 80% of human infections with Lassa virus are mild or asymptomatic, and 1% of infections overall result in death (1). On August 28, 2004, a man aged 38 years residing in New Jersey died from Lassa fever after returning from travel to West Africa. This report summarizes the clinical and epidemiologic investigations conducted by federal, state, and local public health agencies. The findings illustrate the need for clinicians and public health officials to remain alert to emerging infectious diseases and to institute appropriate measures to promptly identify and limit spread of unusual pathogens.

Investigation:

An investigation was conducted to identify persons who might have had direct contact with the patient or his body fluids while he was ill. Contacts were categorized into low- and high-risk categories on the basis of multiple criteria (Box).

A total of 188 persons had contact with the patient during the period when he was likely infectious; of these, five persons were classified as at high risk and 183 as at low risk. The five at high risk were the patient's wife, three of their children, and the patient's brother, who was a hospital visitor; each reportedly had unprotected exposure to the patient's body fluids during his illness. Contacts at low risk included nine other family members, 139 health-care workers employed at the Trenton hospital (including 42 laboratory workers, 32 nurses, and 11 physicians), and 16 laboratory workers employed at commercial laboratories in Virginia and California. In addition, 19 contacts at low risk were exposed as passengers on the flight from London to Newark.

The NJDHSS notified CDC's Division of Global Migration and Quarantine (DGMQ) of possible travel-related exposures. Because the patient reported illness onset 3 days before air travel, DGMQ searched for those airline passengers who had been seated within 6 feet of the patient. Passengers were traced by using information from travel reservation records and customs declaration forms. Nineteen passengers seated near the patient were identified (Figure 2). Within 5 days of notification, 13 of the 19 passengers had been interviewed; within 8 days, three more had been contacted. The remaining three could not be contacted. Seventeen of 19 passengers were citizens of the United Kingdom, and authorities in that country were notified; two of the passengers were U.S. citizens. Interviewed passengers did not report contact with the patient's body fluids and were considered to have low-risk exposure. All passengers contacted were healthy; none reported fever as of September 14, which marked the end of the 21-day incubation period for Lassa fever for this group.

All contacts at high risk (i.e., five family members) were monitored for temperature of >101^ºF (>38.3^ºC) twice daily for 21 days after their last potential exposure to the patient on August 28. A public health nurse visited the family contacts each morning and recorded their temperatures. In the afternoon, the contacts recorded their own temperatures and reported the results.

The majority of contacts at low risk (i.e., nine other family members and 139 health-care workers) were instructed to record their own temperatures at least twice daily and report the results. Other contacts at low risk (i.e., the 16 laboratory workers and 19 air passengers) were asked to self monitor for temperature of >101^ºF (>38.3^ºC) and other symptoms compatible with Lassa fever.

No restriction was placed on work or movement for asymptomatic adults at either high or low risk. However, to facilitate monitoring, the patient's children were restricted from participating in school activities. None of the contacts at high risk reported any illness compatible with Lassa fever as of September 18, which ended their 21-day incubation period.