Pathologic studies on suspect animal and human cases of Rift Valley fever from an outbreak in Eastern Africa, 2006-2007

Abstract

Rift Valley fever (RVF) is an important viral zoonotic disease in Africa with periodic outbreaks associated with severe disease, death, and economic hardship. During the 2006-2007 outbreaks in Eastern Africa, postmortem and necropsy tissue samples from 14 animals and 20 humans clinically suspected of RVF were studied with histopathologic evaluation and immunohistochemical (IHC) assays. Six animal and 11 human samples had IHC evidence of Rift Valley fever virus (RVFV) antigens. We found that extensive hepatocellular necrosis without prominent inflammatory cell infiltrates is the most distinctive histopathologic change in liver tissues infected with RVFV. Pathologic studies on postmortem tissue samples can help establish the diagnosis of RVF, differentiating from endemic diseases with clinical manifestations similar to RVF, such as malaria, leptospirosis, or yellow fever.

Figure 1.

(A) Extensive hepatocellular necrosis with acidophilic bodies in a bovine liver. Hematoxylin-eosin staining. Original magnification, ×100. (B) Positive staining of Rift Valley fever (RVF) viral antigens in necrotic hepatocytes of the bovine liver. Immunoalkaline phosphate staining, naphthol fast red substrate with light hematoxylin counterstain. Original magnification, ×100. (C) Extensive hepatocellular necrosis with acidophilic bodies in a human liver. Hematoxylin-eosin staining. Original magnification, ×200. (D) Positive staining of RVF viral antigens in necrotic hepatocytes of the human liver. Immunoalkaline phosphate staining, naphthol fast red substrate with light hematoxylin counterstain. Original magnification, ×200. (E) Extensive hepatocellular necrosis with Cowdry type A intranuclear inclusions and multinucleated cells in a human liver. Hematoxylin-eosin staining. Original magnification, ×400. (F) Positive staining of human herpes simplex viral antigens in hepatocytes of the human liver. Immunoalkaline phosphate staining, naphthol fast red substrate with light hematoxylin counterstain. Original magnification, ×400.

Figure 2.

(A) Focal interstitial inflammation, acute tubular necrosis, and fibrinous casts in a human kidney. Hematoxylin-eosin staining. Original magnification, ×100. (B) Positive staining of Rift Vallye fever (RVF) viral antigens in renal tubules of a human kidney. Immunoalkaline phosphate staining, naphthol fast red substrate with light hematoxylin counterstain. Original magnification, ×100. (C) Intra-erythrocytic parasites (arrow) in the blood vessel of a human muscle. Hematoxylin-eosin staining. Original magnification, ×630. (D) Positive staining of Plasmodium falciparum antigen in red blood cell (arrow) of a human muscle. Immunoalkaline phosphate staining, naphthol fast red substrate with light hematoxylin counterstain. Original magnification, ×630.