Seroprevalence of West Nile Virus specific IgG and IgM antibodies in North-Western and Western provinces of Zambia

Our plain-English summary of Seroprevalence of West Nile Virus specific IgG and IgM antibodies in North-Western and Western provinces of Zambia, by I. Mweene-Ndumba, S. Siziya, M. Monze, et al (African Health Sciences, 2015).

The study

• Authors: I. Mweene-Ndumba, S. Siziya, M. Monze, M.L. Mazaba, F. Masaninga, P. Songolo, P. Mwaba, O.A. Babaniyi
• Journal: African Health Sciences
• Published: 2015;15(3):803-9
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: West Nile Virus (WNV) infection has been reported worldwide, including in Africa but its existence in Zambia is unknown. Symptoms for the virus include headache, myalgia, arthralgia and rash.

Objectives: This study aimed to determine the seroprevalence of WNV and its correlates.

Methods: A cross sectional study was conducted in North-Western and Western provinces of Zambia. Samples were subjected to IgG and IgM antibodies testing against WNV. Logistic regression analyses were conducted to determine magnitudes of association.

Results: A total of 3,625 of persons participated in the survey out of which 10.3% had WNV infection. Farmers were 20% (AOR=0.80; 95% CI [0.64, 0.99]) less likely to have infection compared to students. Meanwhile participants who lived in grass roofed houses were 2.97 (AOR=2.97; 95% CI [1.81, 4.88]) times more likely to be infected than those who lived in asbestos roofed houses. IRS was associated with reduced risk of infection (AOR=0.81; 95% CI [0.69, 0.94]). Travelling to Angola was associated with the infection [AOR=1.40; 95% CI [1.09, 1.81].

Conclusion: Spraying houses with insecticide residual spray would minimize mosquito-man contact. Furthermore, surveillance at the border with Angola should be enhanced in order to reduce importation of the virus into the country.

In plain English

This was a survey of West Nile virus infection, not of asbestos health effects; asbestos appears only as a type of house roof. In total, 3,625 people aged nine months or older in Zambia's North-Western and Western provinces took part. Blood was first tested for yellow fever antibodies, and presumed yellow-fever-positive samples were then tested for West Nile virus antibodies. The authors reported that 10.3% of participants had infection. People living in grass-roofed houses were more likely to be infected than people living in asbestos-roofed houses (adjusted odds ratio 2.97; 95% CI 1.81 to 4.88). Lower odds were linked to living in a house treated with indoor residual spray (AOR 0.81; 95% CI 0.69 to 0.94) and to being a farmer rather than a student (AOR 0.80; 95% CI 0.64 to 0.99). Travel to Angola was linked to higher odds (AOR 1.40; 95% CI 1.09 to 1.81). No significant association with sex was seen. The authors concluded that the infection is prevalent in the two provinces. They noted no confirmatory neutralization test was done, so cross-reacting antibodies to related viruses could have inflated positives.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional survey using two-stage cluster sampling, carried out within a yellow fever risk assessment survey. Samples were first tested for yellow fever antibodies, and presumptive yellow-fever-positive samples were then tested for antibodies to other flaviviruses, including West Nile virus.
• Who was studied: 3,625 people aged 9 months or older living in sampled households in North-Western and Western provinces of Zambia took part in the survey. The article does not state how many of their samples were tested for West Nile virus. The survey date is not stated in the text.
• Exposure: The outcome was West Nile virus infection, defined by IgG or IgM antibodies. The factors examined were age, sex, occupation, education, roof type (grass-roofed compared with asbestos-roofed houses), use of insecticide treated nets and indoor residual spray, and travel to the Democratic Republic of Congo or Angola. The study did not measure asbestos exposure; asbestos roofing served only as the comparison group for roof type.
• Main results:
  • The authors reported that 10.3% of participants had West Nile virus infection. The article does not state how many samples were actually tested for West Nile virus.
  • Participants in grass-roofed houses had higher odds of infection than those in asbestos-roofed houses (AOR 2.97; 95% CI 1.81 to 4.88).
  • Participants whose houses had indoor residual spray had lower odds of infection than those whose houses were not sprayed (AOR 0.81; 95% CI 0.69 to 0.94 in the text).
  • Farmers had lower odds of infection than students (AOR 0.80; 95% CI 0.64 to 0.99).
  • Compared with participants aged 45 years or older, children under 5 years had lower odds of infection (AOR 0.38; 95% CI 0.20 to 0.73), and participants aged 35 to 44 years had higher odds (AOR 1.41; 95% CI 1.01 to 1.97).
  • Participants with primary education had higher odds of infection than those with higher education (AOR 1.32; 95% CI 1.01 to 1.72).
  • Travel to Angola was associated with higher odds of infection (AOR 1.40; 95% CI 1.09 to 1.81).
  • Travel to the Democratic Republic of Congo was associated with lower odds of infection (AOR 0.28; 95% CI 0.10 to 0.74).
  • No significant association was found between infection and sex (p=0.868).
• The authors' conclusion: The authors concluded that West Nile virus infection is prevalent in North-Western and Western provinces of Zambia. They also stated that spraying houses with residual insecticide would reduce mosquito-human contact and that surveillance at the Angola border should be enhanced.
• Limitations the authors state:
  • Results were based only on primary IgG and IgM antibody tests, without a Plaque Reduction Neutralization Test. Because cross-reactivity with related viruses was not taken into account, the authors state this could have inflated the number of positives.
  • The association between West Nile virus and the animal and bird populations in the provinces was not examined.

Related studies

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• An epidemiological survey of immunological abnormalities in asbestos workers. II. Serum immunoglobulin levels — A. Lange (1980)
• Diffuse pleural mesothelioma and asbestos exposure in the North Western Cape Province — J.C. Wagner, C.A. Sleggs, et al. (1960)
• Simian virus 40 large T antigen (SV40LTAg) primer specific DNA amplification in human pleural mesothelioma tissue — C. Pepper, B. Jasani, et al. (1996)
• Comparison of antibodies to HBME-1 and calretinin for the detection of mesothelial cells in effusion cytology — P.A. Fetsch, A. Simsir, et al. (2001)
• Enhancement of the macrophage oxidative burst by immunoglobulin coating of respirable fibers: fiber-specific differences between asbestos and man-made fibers — I.M. Hill, P.H. Beswick, et al. (1996)

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