Disease Updates: Rabies 2020

From the December 2020 Newsletter:

Geographical and species distribution of rabies-positive animals in North Dakota January-September 2020.

Nearly 400 rabies tests have been conducted this year at the VDL, compared with a total of 233 tests the previous year. Due to the current COVID-19 pandemic, the VDL is the only North Dakota state laboratory that is performing the rabies direct fluorescent antibody (DFA) test. Thus far, North Dakota has had 12 positive cases from animals. Most of the positive cases have been skunks (eight of 12), while bats and cattle make up the remaining cases at two each. Figure 1 depicts the geographical and species distribution for the 12 rabies cases.

We also have had 15 inconclusive tests. A test must be considered inconclusive if the sample is insufficient or markedly autolyzed (rotten). Often, the insufficient sample is due to submission of half of the brain in formalin and half of the brain fresh. Full cross-sections of fresh brain, specifically of the brain stem and cerebellum or hippocampus, are required for a valid negative DFA test. However, if any portion of the brain is positive by DFA, the sample is considered positive. Whole fresh brain also is helpful in ruling out other infectious or neoplastic processes. Finally, please remember that when diagnosis of CNS disease is the goal, keep the brain fresh and whole.

For submission tips, see our printable rabies guide.

Featured image credit: Public Health Image Library ID#21620. Caption: Under magnification of 500X, this photomicrograph of a brain tissue specimen, extracted from an unknown source, revealed the presence of intracellular, magenta-colored inclusions known as Negri bodies, in a case of rabies.